Calcium Contributions by FoundHealth

Calcium is the most abundant mineral in the body, making up nearly 2% of total body weight. More than 99% of the calcium in your body is found in your bones, but the other 1% is perhaps just as important for good health. Many enzymes depend on calcium in order to work properly, as do your nerves, heart, and blood-clotting mechanisms.

To build bone, you need to have enough calcium in your diet. But in spite of calcium-fortified orange juice and the best efforts of the dairy industry, most Americans are calcium deficient. ¹ Calcium supplements are a simple way to make sure you're getting enough of this important mineral.

One of the most important uses of calcium is to help prevent and treat osteoporosis, the progressive loss of bone mass to which menopausal women are especially vulnerable. Calcium works best when combined with vitamin D.

Other meaningful evidence suggests that calcium may have an additional important use: reducing PMS symptoms.

Safety Issues

In general, it's safe to take up to 2,500 mg of calcium daily, although this is more than you need. ^{93,119 1} Greatly excessive intake of calcium can cause numerous side effects, including dangerous or painful deposits of calcium within the body.

Note:If you have cancer, hyperparathyroidism, or sarcoidosis, you should take calcium only under a physician's supervision.

Some evidence hints that use of calcium supplements might slightly increase kidney stone risk. ^{96,132,178 2} However, increased intake of calcium from fooddoes not seem to have this effect and could even help prevent stones. ^{94,95,97,132 3} One study found that if calcium supplements are taken with food, there is no increased risk. ^{146 4} Calcium citrate supplements may be particularly safe regarding kidney stones because the citrate portion of this supplement is used to treatkidney stones. ^{147 5} There is preliminary evidence that calcium supplementation in healthy, post-menopausal women may slightly increase the risk of cardiovascular events, such as myocardial infarction. However, it remains far from clear whether this possible risk outweighs the benefits of calcium supplementation in this population. ^{192,194 6} Large observational studies have found that, in men, higher intakes of calcium are associated with an increased risk of prostate cancer. ^{98,99,100,179 7} This seems to be the case whether the calcium comes from milk or from calcium supplements.

Calcium supplements combined with high doses of vitamin D might interfere with some of the effects of drugs in the calcium channel blocker family. ^{101 8} It is very important that you consult your physician before trying this combination.

Concerns have been raised that the aluminum in some antacids may not be good for you. ^{102 9} There is some evidence that calcium citrate supplements might increase the absorption of aluminum; ^{103-107 10 11 12 13} for this reason, it might not be a good idea to take calcium citrate at the same time of day as aluminum-containing antacids. Another option is to use different forms of calcium, or to avoid antacids containing aluminum.

When taken over the long term, thiazide diuretics tend to increase levels of calcium in the body by decreasing the amount excreted by the body. ^{108-111 14 15 16} It's not likely that this will cause a problem. Nonetheless, if you are using thiazide diuretics, you should consult with your physician on the proper doses of calcium and vitamin D for you.

Finally, calcium may interfere with the absorption of antibiotics in the tetracycline and fluoroquinolone families as well as thyroid hormone. ^{112-118 17 18 19 20 21 22} If you are taking any of these drugs, you should take your calcium supplements at least 2 hours before or after your medication dose.

Interactions You Should Know About

• You may need more calcium if you are taking:
  • Corticosteroids
  • Heparin
  • Isoniazid

• If you are taking aluminum hydroxide , you should take calcium citrate at least 2 hours apart to avoid increasing aluminum absorption.

• You may need more calcium if you are taking the following anticonvulsants:
  • Phenytoin (Dilantin)
  • Carbamazepine
  • Phenobarbital
  • Primidone
  • Note:It may be advisable to take your dose of anticonvulsant and your calcium supplement at least 2 hours apart because each interferes with the other's absorption.

• If you are taking the following medications, you should take your calcium supplement at least 2 hours before or after your dose of medication because calcium interferes with the absorption (and vice versa):
  • Antibiotics in the tetracycline or fluoroquinolone (Cipro, Floxin, Noroxin) families
  • Thyroid hormone

• Do not take extra calcium except on the advice of a physician if you are taking Thiazide diuretics.

• Do not take calcium together with high-dose vitamin D except on the advice of a physician if you are taking calcium channel blockers .

• You may need extra calcium if you are taking:
  • Iron
  • Manganese
  • Zinc
  • Chromium
  • Ideally, you should take calcium at a different time of day from these other minerals because it may interfere with their absorption.

• It may be advisable to wait 2 hours after taking calcium supplements to eat soy (or vice versa). A constituent of soy called phytic acid can interfere with the absorption of calcium.

• Taking supplemental calcium may be helpful if you are taking metformin.

Osteoporosis

A number of double-blind, placebo-controlled studies indicate that calcium supplements (especially as calcium citrate, and taken with vitamin D) are slightly helpful in preventing and slowing down bone loss in postmenopausal women. ^{73-76,138,165-169,180 1} Contrary to some reports, milk does appear to be a useful source of calcium for this purpose. ^{183-184 2} However, the effect of calcium supplementation in any form is relatively mild and may not be strong enough to reduce the rate of osteoporotic fractures. Note that use of calcium and vitamin Dmust be continual. Any improvements in bone density rapidly disappear once the supplements are stopped. ^{77 3} A large study of over 3,000 postmenopausal women aged 65-71 years found that three years of daily supplementation with calcium and vitamin D was not associated with a significant reduction in the incidence of fractures. ^{197 4} Calcium carbonate may not be effective. ^{170-171 5} One study found benefits for male seniors using a calcium and vitamin D-fortified milk product. ^{172 6} (See, however, possible increased risk of prostate cancer discussed in Safety Issues .)

Calcium and vitamin D supplementation may help bones heal that have become fractured due to bone thinning. ^{139 7} Calcium supplements may do a better job of strengthening bones when people have relatively high protein intake. ^{125 8} Heavy exercise causes increased calcium loss through sweat, and the the body does not compensate for this by reducing calcium loss in the urine. ^{190 9} The result can be a net calcium loss great enough so that it presents health concerns for menopausal women, already at risk for osteoporosis. One study found that use of an inexpensive calcium supplement (calcium carbonate), taken at a dose of 400 mg twice daily, is sufficient to offset this loss. ^{190 10} Calcium supplementation could, in theory, be useful for young girls as a way to "put calcium in the bank"—building up a supply for the future in order to prevent later osteoporosis. However, surprisingly, the benefits seen in studies have been modest to nonexistent, and this approach may only produce results when exercise is also increased. ^{79-81,140-143,173-175,181 11} One study found that in calcium-deficient pregnant women, calcium supplements can improve the bones of their unborn children. ^{82 12} Evidence suggests that the use of calcium combined with vitamin D can help protect against the bone loss caused by corticosteroid drugs, such as prednisone. A review of five studies covering a total of 274 participants reported that calcium and vitamin D supplementation significantly prevented bone loss in corticosteroid-treated individuals. ^{83 13} For example, in a 2-year, double-blind, placebo-controlled study that followed 65 individuals with rheumatoid arthritis taking low-dose corticosteroids, daily supplementation with 1,000 mg of calcium and 500 IU of vitamin D reversed steroid-induced bone loss, causing a net bone gain. ^{84 14} There is some evidence that essential fatty acids may enhance the effectiveness of calcium. In one study, 65 postmenopausal women were given calcium along with either placebo or a combination of omega-6 fatty acids (from evening primrose oil ) and omega-3 fatty acids (from fish oil ) for a period of 18 months. At the end of the study period, the group receiving essential fatty acids had higher bone density and fewer fractures than the placebo group. ^{85 15} However, a 12-month, double-blind trial of 42 postmenopausal women found no benefit. ^{86 16} The explanation for the discrepancy may lie in the differences between the women studied. The first study involved women living in nursing homes, while the second studied healthier women living on their own. The latter group of women may have been better nourished and already received enough essential fatty acids in their diet.

Premenstrual Syndrome (PMS)

According to a large and well-designed study published in a 1998 issue of American Journal of Obstetrics and Gynecology,calcium supplements are a simple and effective treatment for a wide variety of PMS symptoms. ^{87 17} In a double-blind, placebo-controlled study of 497 women, 1,200 mg daily of calcium as calcium carbonate reduced PMS symptoms by half over a period of three menstrual cycles. These symptoms included mood swings, headaches, food cravings, and bloating. These results corroborate earlier, smaller studies. ^{88,89 18}

High Cholesterol

In a 12-month study of 223 postmenopausal women, use of calcium citrate at a dose of 1 g daily improved the ratio of HDL (“good”) cholesterol levels to LDL (“bad”) cholesterol levels. ^{124 19} The extent of this improvement was statistically significant (as compared to the placebo group), but not very large in practical terms. Similarly modest benefits were seen in a previous, smaller double-blind, placebo-controlled study. ^{63 20} A third double-blind, placebo-controlled study failed to find any statistically significant effects. ^{64 21}

Colon Cancer

Evidence from observational studies showed that a high calcium intake is associated with a reduced incidence of colon cancer , ^{91 22} but not all studies have found this association. ^{92 23} Some but not all evidence from intervention trials supports these findings. ^{90,176-178 24} A 4-year, double-blind, placebo-controlled study followed 832 individuals with a history of colon polyps. ^{90 25} Participants received either 3 g daily of calcium carbonate or placebo. The calcium group experienced 24% fewer polyps overall than the placebo group. Since colon polyps are the precursor of most colon cancer, this finding strongly suggests benefit. Combing the results for two trials, involving a total of 1,346 subjects also with a history of polyps, researchers found that 1,200 mg or 2,000 mg of daily elemental calcium led to a significant reduction in polyp recurrence compared to placebo over a 3-4 year period. ^{193 26} Another, large-sized study found that calcium carbonate at a dose of 1,200 mg daily may have a more pronounced effect on dangerous polyps than on benign ones. ^{144 27} However, a gigantic (36,282 participant), very long-term (average 7 years) study of postmenopausal women failed to find that calcium carbonate supplements at a dose of 1,000 mg daily had any effect on the incidence of colon cancer. ^{178 28} Given these conflicting results, if calcium supplementation does have an effect on colon cancer risk, it is probably small.

Hypertension

A very large randomized, placebo-controlled trial of over 36,000 postmenopausal women found daily supplementation with 1,000 mg of calcium plus 400 IU of vitamin D did not reduce or prevent hypertension during 7 years of follow-up. These results are possibly limited by non-study calcium use. ^{195 29}

According to most, though not all studies, use of calcium (especially in the form of calcium citrate) combined with vitamin D may modestly slow the bone loss that leads to osteoporosis . ^{48-55,151-153 1} A rather surprising potential use of calcium came to light when a large, well-designed study found that calcium is an effective treatment for premenstrual syndrome (PMS). ^{56 2} Calcium supplementation reduced all major symptoms, including headache, food cravings, moodiness, and fluid retention. It is at least remotely possible that there may be a connection between these two uses of calcium: weak evidence hints that PMS might be an early sign of future osteoporosis. ^{57,58 3} One small but carefully conducted study suggests that getting enough calcium may help control symptoms of menstrual pain . ^{89 4} Some, but not all, observational and intervention studies have found evidence that calcium supplementation may reduce the risk of colon cancer . ^{59,134-135,154-156 5} Risk reduction might continue for years after calcium supplements are stopped. ^{182 6} However, calcium supplements might increase risk of prostate cancer in men, as discussed in the Safety Issues section. For menopausal women, calcium supplementation, especially with vitamin D added, may reduce cancer risk in general. ^{187 7} Individuals who are deficient in calcium may be at greater risk of developing high blood pressure . ^{60,61,126 8} Among individuals who already have hypertension, increased intake of calcium might slightly decrease blood pressure, according to some, but not all, studies. ^{62,127 9} Weak evidence hints that use of calcium by pregnant mothers might reduce risk of hypertension in their children. ^{185 10} Calcium supplements might slightly improve the cholesterol profile. ^{63,64,124 11} Calcium supplementation has also been tried as a treatment to prevent preeclampsia in pregnant women. While the evidence from studies is conflicting, ^{66-68,157-15 12} calcium supplementation might offer at least a minimal benefit.

The drug metformin , used for diabetes, interferes with the absorption of vitamin B 12 . Interestingly, calcium supplements may reverse this, allowing the B 12 to be absorbed normally. ^{70 13} Rapid weight loss in overweight postmenopausal women appears to slightly accelerate bone loss. ^{71,136 14} For this reason, it may make sense to take calcium and vitamin D supplements when deliberately losing weight. It has been additionally suggested that calcium supplements, or high-calcium diets, may directly enhance weight loss, but current evidence is more negative than positive. ^{72,130,137,159-165,186,188,189,191 15} Finally, calcium is also sometimes recommended for attention deficit disorder , migraine headaches , and periodontal disease , but there is as yet no meaningful evidence that it is effective for these conditions.

It is important to note that despite the benefits of calcium supplementation for certain conditions, a large, placebo-controlled trial involving over 36,000 post-menopausal women found that daily supplements of 1,000 mg of calcium carbonate combined with 400 IU of vitamin D(3) for an average of seven years did not significantly reduce death rates from all causes.196

Unlike some supplements, calcium is not taken at extra high doses for special therapeutic benefit. Rather, for all its uses, it should be taken in the amounts listed under Requirements/Sources, along with the recommended level of vitamin D. (See the article on vitamin D for proper dosage amounts.)

Calcium absorption studies have found evidence that your body can't absorb more than 500 mg of calcium at one time. ^{11 1} Therefore, it is most efficient to take your total daily calcium in two or more doses.

Use of prebiotics known as "inulin fructans" may improve calcium absorption. ^{149 2} It isn't possible to put all the calcium you need in a single multivitamin/mineral tablet, so this is one supplement that should be taken on its own. Furthermore, if taken at the same time, calcium may interfere with the absorption of chromium and manganese . ^{12,13,14 3} This means that it is best to take your multivitamin and mineral pill at a separate time from your calcium supplement.

Although the calcium present in some antacids or supplements may alter the absorption of magnesium , this effect apparently has no significant influence on overall magnesium status. ^{15,16 4} Calcium may also interfere with iron absorption, ^{17-22, 150 5 6} but the effect may be too slight to cause a problem. Some studies show that calcium may decrease zinc absorption when the two are taken together as supplements; however, studies have found that, in the presence of meals, zinc levels may be unaffected by increases of either dietary or supplemental calcium. ^{23-29 7 8 9 10 11 12}

References

1. McCarron DA. Dietary calcium and lower blood pressure: we can all benefit [editorial]. JAMA. 1996;275:1128-1129.
2. Bourgoin BP, Evans DR, Cornett JR, et al. Lead content in 70 brands of dietary calcium supplements. Am J Public Health. 1993;83:1155-1160.
3. Ross EA, Szabo NJ, Tebbett IR. Lead content of calcium supplements. JAMA. 2000;284:1425-1429.
4. Heaney RP. Lead in calcium supplements: cause for alarm or celebration? JAMA. 2000;284:1432-1433.
5. Heller HJ, Greer LG, Haynes SD, et al. Pharmacokinetic and pharmacodynamic comparison of two calcium supplements in postmenopausal women. J Clin Pharmacol. 2000;40:1237-1244.
6. Heller HJ, Stewart A, Haynes S, et al. Pharmacokinetics of calcium absorption from two commercial calcium supplements. J Clin Pharmacol. 1999;39:1151-1154.
7. Dawson-Hughes B, Dallal GE, Krall EA, et al. A controlled trial of the effect of calcium supplementation on bone density in postmenopausal women. N Engl J Med. 1990;323:878-883.
8. Sheikh MS, Santa Ana CA, Nicar MJ, et al. Gastrointestinal absorption of calcium from milk and calcium salts. N Engl J Med. 1987;317:532-536.
9. Miller JZ, Smith DL, Flora L, et al. Calcium absorption from calcium carbonate and a new form of calcium (CCM) in healthy male and female adolescents. Am J Clin Nutr. 1988;48:1291-1294.
10. Heller HJ, Greer LG, Haynes SD, et al. Pharmacokinetic and pharmacodynamic comparison of two calcium supplements in postmenopausal women. J Clin Pharmacol. 2000;40:1237-1244.
11. Harvey JA, Zobitz MM, Pak CY. Dose dependency of calcium absorption: a comparison of calcium carbonate and calcium citrate. J Bone Miner Res. 1988;3:253-258.
12. Seaborn CD, Stoecker BJ. Effects of antacid or ascorbic acid on tissue accumulation and urinary excretion of 51 chromium. Nutr Res. 1990;10:1401-1407.
13. Freeland-Graves JH, Lin PH. Plasma uptake of manganese as affected by oral loads of manganese, calcium, milk, phosphorus, copper, and zinc. J Am Coll Nutr. 1991;10:38-43.
14. Davidsson L, Cederblad A, Lonnerdal B, et al. The effect of individual dietary components on manganese absorption in humans. Am J Clin Nutr. 1991;54:1065-1070.
15. Lewis NM, Marcus MS, Behling AR, et al. Calcium supplements and milk: effects on acid-base balance and on retention of calcium, magnesium, and phosphorus. Am J Clin Nutr. 1989;49:527-533.
16. Andon MB, Ilich JZ, Tzagournis MA, et al. Magnesium balance in adolescent females consuming a low- or high-calcium diet. Am J Clin Nutr. 1996;63:950-953.
17. Hallberg L. Does calcium interfere with iron absorption? Am J Clin Nutr. 1998;68:3-4.
18. Minihane AM, Fairweather-Tait SJ. Effect of calcium supplementation on daily nonheme-iron absorption and long-term iron status. Am J Clin Nutr. 1998;68:96-102.
19. Cook JD, Dassenko SA, Whittaker P. Calcium supplementation: effect on iron absorption. Am J Clin Nutr. 1991;53:106-111.
20. Dawson-Hughes B, Seligson FH, Hughes VA. Effects of calcium carbonate and hydroxyapatite on zinc and iron retention in postmenopausal women. Am J Clin Nutr. 1986;44:83-88.
21. Read MH, Medeiros D, Bendel R, et al. Mineral supplementation practices of adults in seven western states. Nutr Res. 1986;6:375-383.
22. Sokoll LJ, Dawson-Hughes B. Calcium supplementation and plasma ferritin concentrations in premenopausal women. Am J Clin Nutr. 1992;56:1045-1048.
23. Argiratos V, Samman S. The effect of calcium carbonate and calcium citrate on the absorption of zinc in healthy female subjects. Eur J Clin Nutr. 1994;48:198-204.
24. Spencer H, Kramer L, Norris C, et al. Effect of calcium and phosphorus on zinc metabolism in man. Am J Clin Nutr. 1984;40:1213-1218.
25. Dawson-Hughes B, Seligson FH, Hughes VA. Effects of calcium carbonate and hydroxyapatite on zinc and iron retention in postmenopausal women. Am J Clin Nutr. 1986;44:83-88.
26. Spencer H, Norris C, Osis D. Further studies of the effect of zinc on intestinal absorption of calcium in man. J Am Coll Nutr. 1992;11:561-566.
27. Hwang SJ, Lai YH, Chen HC, et al. Comparisons of the effects of calcium carbonate and calcium acetate on zinc tolerance test in hemodialysis patients. Am J Kid Dis. 1992;19:57-60.
28. Pecoud A, Donzel P, Schelling JL, et al. Effect of foodstuffs on the absorption of zinc sulfate. Clin Pharmacol Ther. 1975;17:469-474.
29. Crowther RS, Marriott C. Counter-ion binding to mucus glycoproteins. J Pharm Pharmacol. 1984;36:21-26.
30. Buckley LM, Leib ES, Cartularo KS, et al. Calcium and vitamin D 3 supplementation prevents bone loss in the spine secondary to low-dose corticosteroids in patients with rheumatoid arthritis. A randomized, double-blind, placebo-controlled trial. Ann Intern Med. 1996;125:961-968.
31. Reid IR, Ibbertson HK. Calcium supplements in the prevention of steroid-induced osteoporosis. Am J Clin Nutr. 1986;44:287-290.
32. Homik J, Suarez-Almazor ME, Shea B, et al. Calcium and vitamin D for corticosteroid-induced osteoporosis. Cochrane Database Syst Rev. 2000;CD000952.
33. Aarskog D, Aksnes L, Markestad T, et al. Heparin-induced inhibition of 1,25-dihydroxyvitamin D formation. Am J Obstet Gynecol. 1984;148:1141-1142.
34. Haram K, Hervig T, Thordarson H, et al. Osteopenia caused by heparin treatment in pregnancy. Acta Obstet Gynecol Scand. 1993;72:674-675.
35. Wise PH, Hall AJ. Heparin-induced osteopenia in pregnancy. Br Med J. 1980;281:110-111.
36. Brodie MJ, Boobis AR, Dollery CT, et al. Rifampicin and vitamin D metabolism. Clin Pharmacol Ther. 1980;27:810-814.
37. Brodie MJ, Boobis AR, Hillyard CJ, et al. Effect of isoniazid on vitamin D metabolism and hepatic monooxygenase activity. Clin Pharmacol Ther. 1981;30:363-367.
38. Williams SE, Wardman AG, Taylor GA, et al. Long term study of the effect of rifampicin and isoniazid on vitamin D metabolism. Tubercle. 1985;66:49-54.
39. Wahl TO, Gobuty AH, Lukert BP. Long-term anticonvulsant therapy and intestinal calcium absorption. Clin Pharmacol Ther. 1981;30:506-512.
40. Weinstein RS, Bryce GF, Sappington LJ, et al. Decreased serum ionized calcium and normal vitamin D metabolite levels with anticonvulsant drug treatment. J Clin Endocrinol Metab. 1984;58:1003-1009.
41. Hahn TJ, Hendin BA, Scharp CR. Effect of chronic anticonvulsant therapy on serum 25-hydroxycalciferol levels in adults. N Engl J Med. 1972;287:900-904.
42. Jubiz W, Haussler MR, McCain TA, et al. Plasma 1,25-dihydroxyvitamin D levels in patients receiving anticonvulsant drugs. J Clin Endocrinol Metab. 1977;44:617-621.
43. Williams C, Netzloff M, Folkerts L, et al. Vitamin D metabolism and anticonvulsant therapy: effect of sunshine on incidence of osteomalacia. South Med J. 1984;77:834-836.
44. Brodie MJ, Boobis AR, Dollery CT, et al. Rifampicin and vitamin D metabolism. Clin Pharmacol Ther. 1980;27:810-814.
45. Tomita S, Ohnishi J, Nakano M, et al. The effects of anticonvulsant drugs on vitamin D 3 -activating cytochrome P -450-linked monooxygenase systems. J Steroid Biochem Mol Biol. 1991;39:479-485.
46. Carter BL, Garnett WR, Pellock JM, et al. Effect of antacids on phenytoin bioavailability. Ther Drug Monit. 1981;3:333-340.
47. McElnay JC, Uprichard G, Collier PS. The effect of activated dimethicone and a proprietary antacid preparation containing this agent on the absorption of phenytoin. Br J Clin Pharmacol. 1982;13:501-505.
48. Cumming RG. Calcium intake and bone mass: a quantitative review of the evidence. Calcif Tissue Int. 1990;47:194-201.
49. Dawson-Hughes B, Dallal GE, Krall EA, et al. A controlled trial of the effect of calcium supplementation on bone density in postmenopausal women. N Engl J Med. 1990;323:878-883.
50. Peacock M, Liu G, Carey M, et al. Effect of calcium or 25OH vitamin D 3 dietary supplementation on bone loss at the hip in men and women over the age of 60. J Clin Endocrinol Metab. 2000;85:3011-3019.
51. Prince RL. Diet and the prevention of osteoporotic fractures [editorial]. N Engl J Med. 1997;337:701-702.
52. Nieves JW, Komar L, Cosman F, et al. Calcium potentiates the effect of estrogen and calcitonin on bone mass: review and analysis. Am J Clin Nutr. 1998;67:18-24.
53. Lloyd T, Andon MB, Rollings N, et al. Calcium supplementation and bone mineral density in adolescent girls. JAMA. 1993;270:841-844.
54. Dawson-Hughes B, Harris SS, Krall EA, et al. Effect of withdrawal of calcium and vitamin D supplements on bone mass in elderly men and women. Am J Clin Nutr. 2000;72:745-750.
55. Barr SI, Petit MA, Vigna YM, et al. Eating attitudes and habitual calcium intake in peripubertal girls are associated with initial bone mineral content and its change over 2 years. J Bone Miner Res. 2001;16:940-947.
56. Thys-Jacobs S, Starkey P, Bernstein D, et al. Calcium carbonate and the premenstrual syndrome: effects on premenstrual and menstrual symptoms. Premenstrual Syndrome Study Group. Am J Obstet Gynecol. 1998;179:444-452.
57. Thys-Jacobs S, Silverton M, Alvir J, et al. Reduced bone mass in women with premenstrual syndrome. J Women's Health. 1995;4:161-168.
58. Lee SJ, Kanis JA. An association between osteoporosis and premenstrual symptoms and postmenopausal symptoms. Bone Miner. 1994;24:127-134.
59. Baron JA, Beach M, Mandel JS, et al. Calcium supplements for the prevention of colorectal adenomas. Calcium Polyp Prevention Study Group. N Engl J Med. 1999;340:101-107.
60. Cappuccio FP, Elliot P, Allender PS, et al. Epidemiologic association between dietary calcium intake and blood pressure: a meta-analysis of published data. Am J Epidemiol. 1995;142:935-945.
61. Van Leer EM, Seidell JC, Kromhout D. Dietary calcium, potassium, magnesium and blood pressure in the Netherlands. Int J Epidemiol. 1995;24:1117-1123.
62. Bostick RM, Fosdick L, Grandits GA, et al. Effect of calcium supplementation on serum cholesterol and blood pressure: a randomized, double-blind, placebo-controlled, clinical trial. Arch Fam Med. 2000;9:31-39.
63. Bell L, Halstenson CE, Halstenson CJ, et al. Cholesterol-lowering effects of calcium carbonate in patients with mild to moderate hypercholesterolemia. Arch Intern Med. 1992;152:2441-2444.
64. Bostick RM, Fosdick L, Grandits GA, et al. Effect of calcium supplementation on serum cholesterol and blood pressure: a randomized, double-blind, placebo-controlled, clinical trial. Arch Fam Med. 2000;9:31-39.
65. Thys-Jacobs S, Donovan D, Papadopoulos A, et al. Vitamin D and calcium dysregulation in the polycystic ovarian syndrome. Steroids. 1999;64:430-435.
66. Levine RJ, Hauth JC, Curet LB, et al. Trial of calcium to prevent preeclampsia. N Engl J Med. 1997;337:69-76.
67. Villar J, Belizan JM. Same nutrient, different hypotheses: disparities in trials of calcium supplementation during pregnancy. Am J Clin Nutr. 2000;71(suppl):1375S-1379S.
68. Crowther CA, Hiller JE, Pridmore B, et al. Calcium supplementation in nulliparous women for the prevention of pregnancy-induced hypertension, preeclampsia and preterm birth: an Australian randomized trial. FRACOG and the ACT Study Group. Aust N Z J Obstet Gynaecol. 1999;39:12-18.
69. Hertz-Picciotto I, Schramm M, Watt-Morse M, et al. Patterns and determinants of blood lead during pregnancy. Am J Epidemiol. 2000;152:829-837.
70. Bauman WA, Shaw S, Jayatilleke E, et al. Increased intake of calcium reverses vitamin B 12 malabsorption induced by metformin. Diabetes Care. 2000;23:1227-1231.
71. Chao D, Espeland MA, Farmer D, et al. Effect of voluntary weight loss on bone mineral density in older overweight women. J Am Geriatr Soc. 2000;48:753-759.
72. Davies KM, Heaney RP, Recker RR, et al. Calcium intake and body weight. J Clin Endocrinol Metab. 2000;85:4635-4638.
73. Cumming RG. Calcium intake and bone mass: a quantitative review of the evidence. Calcif Tissue Int. 1990;47:194-201.
74. Dawson-Hughes B, Dallal GE, Krall EA, et al. A controlled trial of the effect of calcium supplementation on bone density in postmenopausal women. N Engl J Med. 1990;323:878-883.
75. Peacock M, Liu G, Carey M, et al. Effect of calcium or 25OH vitamin D 3 dietary supplementation on bone loss at the hip in men and women over the age of 60. J Clin Endocrinol Metab. 2000;85:3011-3019.
76. Prince RL. Diet and the prevention of osteoporotic fractures [editorial]. N Engl J Med. 1997;337:701-702.
77. Dawson-Hughes B, Harris SS, Krall EA, et al. Effect of withdrawal of calcium and vitamin D supplements on bone mass in elderly men and women. Am J Clin Nutr. 2000;72:745-750.
78. Nieves JW, Komar L, Cosman F, et al. Calcium potentiates the effect of estrogen and calcitonin on bone mass: review and analysis. Am J Clin Nutr. 1998;67:18-24.
79. Lloyd T, Andon MB, Rollings N, et al. Calcium supplementation and bone mineral density in adolescent girls. JAMA. 1993;270:841-844.
80. Barr SI, Petit MA, Vigna YM, et al. Eating attitudes and habitual calcium intake in peripubertal girls are associated with initial bone mineral content and its change over 2 years. J Bone Miner Res. 2001;16:940-947.
81. Lloyd T, Chinchilli VM, Johnson-Rollings N, et al. Adult female hip bone density reflects teenage sports-exercise patterns but not teenage calcium intake. Pediatrics. 2000;106:40-44.
82. Koo WW, Walters JC, Esterlitz J, et al. Maternal calcium supplementation and fetal bone mineralization. Obstet Gynecol. 1999;94:577-582.
83. Homik J, Suarez-Almazor ME, Shea B, et al. Calcium and vitamin D for corticosteroid-induced osteoporosis. Cochrane Database Syst Rev. 2000;CD000952.
84. Buckley LM, Leib ES, Cartularo KS, et al. Calcium and vitamin D 3 supplementation prevents bone loss in the spine secondary to low-dose corticosteroids in patients with rheumatoid arthritis. A randomized, double-blind, placebo-controlled trial. Ann Intern Med. 1996;125:961-968.
85. Kruger MC, Coetzer H, de Winter R, et al. Calcium, gamma-linolenic acid and eicosapentaenoic acid supplementation in senile osteoporosis. Aging (Milano). 1998;10:385-394.
86. Bassey EJ, Littlewood JJ, Rothwell MC, et al. Lack of effect of supplementation with essential fatty acids on bone mineral density in healthy pre- and postmenopausal women: two randomized controlled trials of Efacal® v. calcium alone. Br J Nutr. 2000;83:629-635.
87. Thys-Jacobs S, Starkey P, Bernstein D, et al. Calcium carbonate and the premenstrual syndrome: effects on premenstrual and menstrual symptoms. Premenstrual Syndrome Study Group. Am J Obstet Gynecol. 1998;179:444-452.
88. Thys-Jacobs S, Ceccarelli S, Bierman A, et al. Calcium supplementation in premenstrual syndrome: a randomized crossover trial. J Gen Intern Med. 1989;4:183-189.
89. Penland JG, Johnson PE. Dietary calcium and manganese effects on menstrual cycle symptoms. Am J Obstet Gynecol. 1993;168:1417-1423.
90. Baron JA, Beach M, Mandel JS, et al. Calcium supplements for the prevention of colorectal adenomas. Calcium Polyp Prevention Study Group. N Engl J Med. 1999;340:101-107.
91. Hyman J, Baron JA, Dain BJ, et al. Dietary and supplemental calcium and the recurrence of colorectal adenomas. Cancer Epidemiol Biomarkers Prev. 1998;7:291-295.
92. Kearney J, Giovannucci E, Rimm E, et al. Calcium, vitamin D, and dairy foods and the occurrence of colon cancer in men. Am J Epidemiol. 1996;143:907-917.
93. National Institutes of Health Continuing Medical Education. Optimal calcium intake. Nutrition. 1995;11:409-417.
94. Curhan GC, Willett WC, Speizer FE, et al. Comparison of dietary calcium with supplemental calcium and other nutrients as factors affecting the risk for kidney stones in women. Ann Intern Med. 1997;126:497-504.
95. Curhan GC, Willett WC, Rimm EB, et al. A prospective study of dietary calcium and other nutrients and the risk of symptomatic kidney stones. N Engl J Med. 1993;328:833-838.
96. Curhan GC, Willett WC, Speizer FE, et al. Comparison of dietary calcium with supplemental calcium and other nutrients as factors affecting the risk for kidney stones in women. Ann Intern Med. 1997;126:497-504.
97. Parivar F, Low RK, Stoller ML. The influence of diet on urinary stone disease. J Urol. 1996;155:432-440.
98. Giovannucci E, Rimm EB, Wolk A, et al. Calcium and fructose intake in relation to risk of prostate cancer. Cancer Res. 1998;58:442-447.
99. Chan JM, Giovannucci E, Andersson SO, et al. Dairy products, calcium, phosphorous, vitamin D, and risk of prostate cancer (Sweden). Cancer Causes Control. 1998;9:559-566.
100. Giovannucci E. Dietary influences of 1,25(OH)2 vitamin D in relation to prostate cancer: a hypothesis. Cancer Causes Control. 1998;9:567-582.
101. Bar-Or D, Gasiel Y. Calcium and calciferol antagonise effect of verapamil in atrial fibrillation. Br Med J (Clin Res Ed). 1981;282:1585-1586.
102. Gaby AR. Aluminum: the ubiquitous poison. Nutr Healing. 1997;4:3-4,11.
103. Walker JA, Sherman RA, Cody RP. The effect of oral bases on enteral aluminum absorption. Arch Intern Med. 1990;150:2037-2039.
104. Preliminary findings suggest calcium citrate supplements may raise aluminum levels in blood, urine. Fam Pract News. 1992;22:74-75.
105. Weberg R, Berstad A. Gastrointestinal absorption of aluminium from single doses of aluminium containing antacids in man. Eur J Clin Invest. 1986;16:428-432.
106. Nolan CR, Califano JR, Butzin CA. Influence of calcium acetate or calcium citrate on intestinal aluminum absorption. Kidney Int. 1990;38:937-941.
107. Slanina P, Frech W, Bernhardson A, et al. Influence of dietary factors on aluminium absorption and retention in the brain and bone of rats. Acta Pharmacol Toxicol (Copenh). 1985;56:331-336.
108. Riis B, Christiansen C. Actions of thiazide on vitamin D metabolism: a controlled therapeutic trial in normal women early in the postmenopause. Metabolism. 1985;34:421-424.
109. Lemann J Jr, Gray RW, Maierhofer WJ, et al. Hydrochlorothiazide inhibits bone resorption in men despite experimentally elevated serum 1,25-dihydroxyvitamin D concentrations. Kidney Int. 1985;28:951-958.
110. Crowe M, Wollner L, Griffiths RA. Hypercalcaemia following vitamin D and thiazide therapy in the elderly. Practitioner. 1984;228:312-313.
111. Gora ML, Seth SK, Bay WH, et al. Milk-alkali syndrome associated with use of chlorothiazide and calcium carbonate. Clin Pharm. 1989;8:227-229.
112. Neuvonen PJ, Kivisto KT, Lehto P. Interference of dairy products with the absorption of ciprofloxacin. Clin Pharmacol Ther. 1991;50:498-502.
113. Minami R, Inotsume N, Nakano M, et al. Effect of milk on absorption of norfloxacin in healthy volunteers. J Clin Pharmacol. 1993;33:1238-1240.
114. Lehto P, Kivisto KT. Different effects of products containing metal ions on the absorption of lomefloxacin. Clin Pharmacol Ther. 1994;56:477-482.
115. Dudley MN, Marchbanks CR, Flor SC, et al. The effect of food or milk on the absorption kinetics of ofloxacin. Eur J Clin Pharmacol. 1991;41:569-571.
116. Flor S, Guay DR, Opsahl JA, et al. Effects of magnesium-aluminum hydroxide and calcium carbonate antacids on bioavailability of ofloxacin. Antimicrob Agents Chemother. 1990;34:2436-2438.
117. Butner LE, Fulco PP, Feldman G. Calcium carbonate-induced hypothyroidism [letter]. Ann Intern Med. 2000;132:595.
118. Singh N, Singh PN, Hershman JM. Effect of calcium carbonate on the absorption of levothyroxine. JAMA. 2000;283:2822-2825.
119. Dietary reference intakes for calcium, phosphorus, magnesium, vitamin D, and fluoride (1997). The National Academies of Press website. Available at http://www.nap.edu . Accessed October 4, 2001.
120. Borghi L, Schianchi T, Meschi T, et al. Comparison of two diets for the prevention of recurrent stones in idiopathic hypercalciuria. N Engl J Med. 2002;346:77-84.
121. Recker RR. Calcium absorption and achlorhydria. N Engl J Med. 1985;313:70-73.
122. Heaney RP, Dowell MS, Bierman J, et al. Absorbability and cost effectiveness in calcium supplementation. J Am Coll Nutr. 2001;20:239-246.
123. Heaney RP, Dowell MS, Barger-Lux MJ. Absorption of calcium as the carbonate and citrate salts, with some observations on method. Osteoporos Int. 1999;9:19-23.
124. Reid IR, Mason B, Horne A, et al. Effects of calcium supplementation on serum lipid concentrations in normal older women: A randomized controlled trial. Am J Med. 2002;112:343-347.
125. Dawson-Hughes B, Harris S. Calcium intake influences the association of protein intake with rates of bone loss in elderly men and women. Am J Clin Nutr. 2002;75:773-779.
126. Porsti I, Makynen H. Dietary calcium intake: effects on central blood pressure control. Semin Nephrol. 1995;15:550-563.
127. Griffith LE, Guyatt GH, Cook RJ, Bucher HC, Cook DJ. The influence of dietary and nondietary calcium supplementation on blood pressure: an updated metaanalysis of randomized controlled trials. Am J Hypertens. 1999;12(1 Pt 1):84-92.
128. Narva M, Karkkainen M, Poussa T, et al. Caseinphosphopeptides in milk and fermented mild do not affect calcium metabolism acutely in postmenopausal women. J Am Coll Nutr. 2003;22:88-93.
129. Tahiri M, Tressol JC, Arnaud J, et al. Effect of short-chain fructooligosaccharides on intestinal calcium absorption and calcium status in postmenopausal women: a stable-isotope study. Am J Clin Nutr. 2003;77:449-457.
130. Barr SI. Increased dairy product or calcium intake: is body weight or composition affected in humans? J Nutr. 2003;133:245S-248S.
131. Hernandez-Avila M, Gonzalez-Cossio T, Hernandez-Avila JE, et al. Dietary calcium supplements to lower blood lead levels in lactating women: a randomized, placebo-controlled trial. Epidemiology. 2003;14:206-121.
132. Heller HJ, Doerner MF, Brinkley LJ, et al. Effect of dietary calcium on stone forming propensity. J Urol. 2003;169:470-474.
133. Fujita T, Ohue M, Fujii Y, et al. Reappraisal of Katsuragi Calcium study, a prospective, double-blind, placebo-controlled study of the effect of active absorbable algal calcium (AAAC) on vertebral deformity and fracture. J Bone Miner Metab. 2003;22:32-38.
134. Grau MV, Baron JA, Sandler RS, et al. Vitamin D, calcium supplementation, and colorectal adenomas: results of a randomized trial. J Natl Cancer Inst. 2003; 95: 1765-1771.
135. Wallace K, Baron JA, Cole BF, et al. Effect of calcium supplementation on the risk of large bowel polyps. J Natl Cancer Inst. 2004;96:921-925.
136. Cifuentes M, Riedt CS, Brolin RE, et al. Weight loss and calcium intake influence calcium absorption in overweight postmenopausal women. Am J Clin Nutr. 2004;80:123-130.
137. Zemel MB, Thompson W, Milstead A, et al. Calcium and dairy acceleration of weight and fat loss during energy restriction in obese adults. Obes Res. 2004;12:582-590.
138. Shea B, Wells G, Cranney A, et al. Calcium supplementation on bone loss in postmenopausal women. Cochrane Database Syst Rev . 2003;4:CD004526.
139. Doetsch AM, Faber J, Lynnerup N, et al. The effect of calcium and vitamin D(3) supplementation on the healing of the proximal humerus fracture: a randomized placebo-controlled study. Calcif Tissue Int. 2004 May 27. [Epub ahead of print]
140. Dodiuk-Gad RP, Rozen GS, Rennert G, et al. Sustained effect of short-term calcium supplementation on bone mass in adolescent girls with low calcium intake. Am J Clin Nutr. 2005;81:168-174.
141. Matkovic V, Goel PK, Badenhop-Stevens NE, et al. Calcium supplementation and bone mineral density in females from childhood to young adulthood: a randomized controlled trial. Am J Clin Nutr. 2005;81:175-188.
142. Molgaard C, Thomsen BL, Michaelsen KF, et al. Effect of habitual dietary calcium intake on calcium supplementation in 12-14 year old girls. Am J Clin Nutr. 2004;80:1422-1427.
143. Cameron MA, Paton LM, Nowson CA, et al. The effect of calcium supplementation on bone density in premenarcheal females: a co-twin approach. J Clin Endocrinol Metab. 2004;89:4916-4922.
144. Wallace K, Baron JA, Cole BF, et al. Effect of calcium supplementation on the risk of large bowel polyps. J Natl Cancer Inst. 2004;96:921-925.
145. Grau MV, Baron JA, Sandler RS, et al. Vitamin D, calcium supplementation, and colorectal adenomas: results of a randomized trial. J Natl Cancer Inst. 2003; 95:1765-1771.
146. Domrongkitchaiporn S, Sopassathit W, Stitchantrakul W, et al. Schedule of taking calcium supplement and the risk of nephrolithiasis. Kidney Int. 2004;65:1835-1841.
147. Sakhaee K, Poindexter JR, Griffith CS, et al. Stone forming risk of calcium citrate supplementation in healthy postmenopausal women. J Urol. 2004;172:958-961.
148. Heaney RP, Rafferty K, Dowell MS, et al. Calcium fortification systems differ in bioavailability. J Am Diet Assoc. 2005;105:807-809.
149. Abrams SA, Griffin IJ, Hawthorne KM, et al. A combination of prebiotic short- and long-chain inulin-type fructans enhances calcium absorption and bone mineralization in young adolescents. Am J Clin Nutr. 2005;82:471-476.
150. Molgaard C, Kaestel P, Michaelsen KF, et al. Long-term calcium supplementation does not affect the iron status of 12-14-y-old girls. Am J Clin Nutr. 2005;82:98-102.
151. Porthouse J, Cockayne S, King C, et al. Randomised controlled trial of calcium and supplementation with cholecalciferol (vitamin D3) for prevention of fractures in primary care. BMJ. 2005;330:1003.
152. Wactawski-Wende J, Kotchen JM, Anderson GL, et al. Calcium plus vitamin D supplementation and the risk of colorectal cancer. JAMA. 2006;354:684-696.
153. Prince RL, Devine A, Dhaliwal SS, et al. Effects of calcium supplementation on clinical fracture and bone structure: results of a 5-year, double-blind, placebo-controlled trial in elderly women. Arch Intern Med. 2006;166:869-875.
154. Sandler RS. Calcium supplements to prevent colorectal adenomas. Am J Gastroenterol. 2005;100:395-396.
155. Holt PR, Bresalier RS, Ma CK, et al. Calcium plus vitamin D alters preneoplastic features of colorectal adenomas and rectal mucosa. Cancer. 2005 Dec 13. [Epub ahead of print].
156. Wactawski-Wende J, Kotchen JM, Anderson GL, et al. Calcium plus vitamin D supplementation and the risk of colorectal cancer. N Engl J Med. 2006;354:684-696.
157. Atallah AN, Hofmeyr GJ, Duley L. Calcium supplementation during pregnancy for preventing hypertensive disorders and related problems [review]. Cochrane Database Syst Rev. 2002;CD001059.
158. Villar J, Abdel-Aleem H, Merialdi M, et al. World Health Organization randomized trial of calcium supplementation among low calcium intake pregnant women. Am J Obstet Gynecol. 2006;194:639-649.
159. Lorenzen JK, Molgaard C, Michaelsen KF, et al. Calcium supplementation for 1 y does not reduce body weight or fat mass in young girls. Am J Clin Nutr. 2006;83:18-23.
160. Boon N, Hul GB, Viguerie N, et al. Effects of 3 diets with various calcium contents on 24-h energy expenditure, fat oxidation, and adipose tissue message RNA expression of lipid metabolism-related proteins. Am J Clin Nutr. 2005;82:1244-1252.
161. Gunther CW, Legowski PA, Lyle RM, et al. Dairy products do not lead to alterations in body weight or fat mass in young women in a 1-y intervention. Am J Clin Nutr. 2005;81:751-756.
162. Reid IR, Horne A, Mason B, et al. Effects of Calcium Supplementation on body weight an dblood pressure in normal older women - a randomized controlled trial. J Clin Endocrinol Metab. 2005 Apr 12. [Epub ahead of print].
163. Zemel MB, Richards J, Mathis S, et al. Dairy augmentation of total and central fat loss in obese subjects. Int J Obes. 2005;29:391-397.
164. Bowen J, Noakes M, Clifton PM, et al. Effect of calcium and dairy foods in high protein, energy-restricted diets on weight loss and metabolic parameters in overweight adults. Int J Obes Relat Metab Disord. 2005 Feb 15. [Epub ahead of print].
165. Zemel MB, Richards J, Milstead A, et al. Effects of calcium and dairy on body composition and weight loss in african-american adults. Obes Res. 2005;13:1218-1225.
166. Prince RL, Devine A, Dhaliwal SS, Dick IM. Effects of Calcium Supplementation on Clinical Fracture and Bone Structure. Arch Intern Med. 2006;166:869-875.
167. Porthouse J, Cockayne S, King C, et al. Randomised controlled trial of calcium and supplementation with cholecalciferol (vitamin D3) for prevention of fractures in primary care. BMJ. 2005;330:1003.
168. Avenell A, Campbell MK, et al. Oral vitamin D3 and calcium for secondary prevention of low-trauma fractures in elderly people (Randomised Evaluation of Calcium Or vitamin D, RECORD): a randomised placebo-controlled trial. Lancet. 2005;365:1621-1628.
169. Wactawski-Wende J, Kotchen JM, Anderson GL, et al. Calcium plus vitamin D supplementation and the risk of colorectal cancer. JAMA. 2006;354:684-696.
170. Prince RL, Devine A, Dhaliwal SS, et al. Effects of calcium supplementation on clinical fracture and bone structure: results of a 5-year, double-blind, placebo-controlled trial in elderly women. Arch Intern Med. 2006;166:869-875.
171. Prince RL, Devine A, Dhaliwal SS, Dick IM. Effects of calcium supplementation on clinical fracture and bone structure. Arch Intern Med. 2006;166:869-875.
172. Daly RM, Bass S, Nowson C. Long-term effects of calcium-vitamin-D(3)-fortified milk on bone geometry and strength in older men. Bone. 2006 May 23. [Epub ahead of print]
173. Barger-Lux MJ, Davies KM, Heaney RP, et al. Calcium supplementation does not augment bone gain in young women consuming diets moderately low in calcium. J Nutr. 2005;135:2362-2366.
174. Courteix D, Jaffre C, Lespessailles E, et al. Cumulative effects of calcium supplementation and physical activity on bone accretion in premenarchal children: a double-blind randomised placebo-controlled trial. Int J Sports Med. 2005;26:332-338.
175. Cheng S, Lyytikainen A, Kroger H, et al. Effects of calcium, dairy product, and vitamin D supplementation on bone mass accrual and body composition in 10-12-y-old girls: a 2-y randomized trial. Am J Clin Nutr. 2005;82:1115-1126.
176. Sandler RS. Calcium supplements to prevent colorectal adenomas. Am J Gastroenterol. 2005;100:395-396.
177. Holt PR, Bresalier RS, Ma CK, et al. Calcium plus vitamin D alters preneoplastic features of colorectal adenomas and rectal mucosa. Cancer. 2005 Dec 13. [Epub ahead of print].
178. Wactawski-Wende J, Kotchen JM, Anderson GL, et al. Calcium plus vitamin D supplementation and the risk of colorectal cancer. N Engl J Med. 2006;354:684-696.
179. Mitrou PN, Albanes D, Pietinen P, et al. Intakes of calcium, dairy products, and prostate cancer risk in the ATBC study. Poster Session; NIH Research Festival; Oct. 18, 2005.
180. Reid IR, Mason B, Horne A, et al. Randomized controlled trial of calcium in healthy older women. Am J Med. 2006;119:777-785.
181. Winzenberg T, Shaw K, Fryer J, et al. Effects of calcium supplementation on bone density in healthy children: meta-analysis of randomised controlled trials. BMJ. 2006 Sep 15. [Epub ahead of print]
182. Grau MV, Baron JA, Sandler RS, et al. Prolonged effect of calcium supplementation on risk of colorectal adenomas in a randomized trial. J Natl Cancer Inst. 2007;99:129-136.
183. Ting GP, Tan SY, Chan SP, et al. A follow-up study on the effects of a milk supplement on bone mineral density of postmenopausal Chinese women in Malaysia. J Nutr Health Aging. 2007;11:69-73.
184. Chee WS, Suriah AR, Chan SP, The effect of milk supplementation on bone mineral density in postmenopausal Chinese women in Malaysia. Osteoporos Int. 2003;14:828-834. [Epub ahead of print]
185. Bergel E, Barros AJ. Effect of maternal calcium intake during pregnancy on children blood pressure: a systematic review of the literature. BMC Pediatr. 2007 Mar 26. [Epub ahead of print]
186. Caan B, Neuhouser M, Aragaki A, et al. Calcium plus vitamin d supplementation and the risk of postmenopausal weight gain. Arch Intern Med. 2007;167:893-902.
187. Lappe JM, Travers-Gustafson D, Davies KM, et al. Vitamin D and calcium supplementation reduces cancer risk: results of a randomized trial. Am J Clin Nutr. 2007;85:1586-1591.
188. Kabrnova-Hlavata K, Hainer V, Gojova M, et al. Calcium intake and the outcome of short-term weight management. Physiol Res. 2007 May 30. [Epub ahead of print]
189. Winzenberg T, Shaw K, Fryer J, et al. Calcium supplements in healthy children do not affect weight gain, height, or body composition. Obesity (Silver Spring). 2007;15:1789-1798.
190. Martin BR, Davis S, Campbell WW, et al. Exercise and calcium supplementation: effects on calcium homeostasis in sportswomen. Med Sci Sports Exerc. 2007;39:1481-1486.
191. Wagner G, Kindrick S, Hertzler S, et al. Effects of various forms of calcium on body weight and bone turnover markers in women participating in a weight loss program. J Am Coll Nutr. 2007;26:456-461.
192. Bolland MJ, Barber PA, Doughty RN, et al. Vascular events in healthy older women receiving calcium supplementation: randomised controlled trial. BMJ. 2008 Jan 15.
193. Weingarten M, Zalmanovici A, Yaphe J. Dietary calcium supplementation for preventing colorectal cancer and adenomatous polyps. Cochrane Database Syst Rev. 2008;CD003548.
194. Reid IR, Bolland MJ. Calcium supplementation and vascular disease. Climacteric. 2008;11:280-286.
195. Margolis KL, Ray RM, Van Horn L, et al. Effect of calcium and vitamin D supplementation on blood pressure: the Women's Health Initiative Randomized Trial. Hypertension. 2008 Nov;52(5):847-55.
196. LaCroix AZ, Kotchen J, Anderson G, et al. Calcium plus vitamin D supplementation and mortality in postmenopausal women: the Women's Health Initiative calcium-vitamin D randomized controlled trial. J Gerontol A Biol Sci Med Sci. 2009;64:559-67.
197. Salovaara K, Tuppurainen M, Kärkkäinen M, et al. Effect of vitamin D3 and calcium on fracture risk in 65- to 71-year old women - a population-based 3-year randomized controlled trial: OSTPRE-FPS study. J Bone Miner Res. 2010 Jan 29 early online.

Calcium is the most abundant mineral in the body, making up nearly 2% of total body weight. More than 99% of the calcium in your body is found in your bones, but the other 1% is perhaps just as important for good health. Many enzymes depend on calcium in order to work properly, as do your nerves, heart, and blood-clotting mechanisms.

To build bone, you need to have enough calcium in your diet. But in spite of calcium-fortified orange juice and the best efforts of the dairy industry, most Americans are calcium deficient. ¹ Calcium supplements are a simple way to make sure you're getting enough of this important mineral.

One of the most important uses of calcium is to help prevent and treat osteoporosis, the progressive loss of bone mass to which menopausal women are especially vulnerable. Calcium works best when combined with vitamin D.

Other meaningful evidence suggests that calcium may have an additional important use: reducing PMS symptoms.

Although there are some variations between recommendations issued by different groups, the official US and Canadian recommendations for daily intake of calcium are as follows:

• Infants
  • 0-6 months: 210 mg
  • 7-12 months: 270 mg

• Children
  • 1-3 years: 500 mg
  • 4-8 years: 800 mg

• Males and Females
  • 9-18 years: 1,300 mg
  • 19-50 years: 1,000 mg
  • 51 years and older: 1,200 mg

• Pregnant and Nursing Women
  • Under 19 years: 1,300 mg
  • 19 years and older: 1,000 mg

To absorb calcium, your body also needs an adequate level of vitamin D (for more information, see the article on Vitamin D ).

Various medications may impair calcium absorption or metabolism, either directly or through effects on vitamin D. People who use these may benefit by taking extra calcium and vitamin D. Implicated medications include corticosteroids , ^{30-32 1 2} heparin , ^{33-35 3 4} isoniazid , ^{36-38 5 6} and anticonvulsants . ^{39-45 7 8 9 10 11 12} Note:Calcium carbonate might interfere with the effects of anticonvulsant drugs, and for that reason should not be taken at the same time of day. ^{46,47 13} Milk, cheese, and other dairy products are excellent sources of calcium. Other good sources include orange juice or soy milk fortified with calcium, fish canned with its bones (such as sardines), dark green vegetables, nuts and seeds, and calcium-processed tofu.

Many forms of calcium supplements are available on the market, each with its own advantages and disadvantages.

Naturally Derived Forms of Calcium

These forms of calcium come from bone, shells, or the earth: bonemeal, oyster shell, and dolomite. Animals concentrate calcium in their shells, and calcium is found in minerals in the earth. These forms of calcium are economical, and you can get as much as 500 mg to 600 mg in one tablet. However, there are concerns that the natural forms of calcium supplements may contain significant amounts of lead. ^{2 14} The level of contamination has decreased in recent years, but still may present a health risk. ^{3,4 15} Calcium supplements rarely list the lead content of their source, although they should. The lead concentration should always be less than 2 parts per million.

Refined Calcium Carbonate

This is the most common commercial calcium supplement, and it is also used as a common antacid. Calcium carbonate is one of the least expensive forms of calcium, but it can cause constipation and bloating, and it may not be well absorbed by people with reduced levels of stomach acid. Taking it with meals improves absorption because stomach acid is released to digest the food. ^{121 16} (See the section, Chelated Calcium, below.)

Chelated Calcium

Chelated calcium is calcium bound to an organic acid (citrate, citrate malate, lactate, gluconate, aspartate, or orotate). The chelated forms of calcium offer some significant advantages and disadvantages compared with calcium carbonate.

Certain forms of chelated calcium (calcium citrate and calcium citrate malate) are widely thought to be significantly better absorbed and more effective for osteoporosis treatment than calcium carbonate. However, while some studies support this belief, ^{6,7,9,10 17} others do not. ^{8,122,123 18} The discrepancy may be due to the particular calcium carbonate products used; some calcium carbonate formulations may dissolve better than others.

One study found that calcium citrate malate in orange juice is markedly better absorbed than tricalcium phosphate/calcium lactate in orange juice. ^{148 19} A form of calcium called active absorbable algal calcium (AAACa) has also been promoted as superior to calcium carbonate, but the study upon which claims of benefit are founded actually used quite questionable statistical methods (technically, post-hoc subgroup analysis). ^{133 20} Chelated calcium is much more expensive and bulkier than calcium carbonate. In other words, you have to take larger pills, and more of them, to get enough calcium. It is not at all uncommon to need to take five or six large capsules daily to supply the necessary amount, a quantity some people may find troublesome.

Osteoporosis

A number of double-blind, placebo-controlled studies indicate that calcium supplements (especially as calcium citrate, and taken with vitamin D) are slightly helpful in preventing and slowing down bone loss in postmenopausal women. ¹ Contrary to some reports, milk does appear to be a useful source of calcium for this purpose. ² However, the effect of calcium supplementation in any form is relatively mild and may not be strong enough to reduce the rate of osteoporotic fractures. Note that use of calcium and vitamin Dmust be continual. Any improvements in bone density rapidly disappear once the supplements are stopped. ³ A large study of over 3,000 postmenopausal women aged 65-71 years found that three years of daily supplementation with calcium and vitamin D was not associated with a significant reduction in the incidence of fractures. ⁴ Calcium carbonate may not be effective. ⁵ One study found benefits for male seniors using a calcium and vitamin D-fortified milk product. ⁶ (See, however, possible increased risk of prostate cancer discussed in Safety Issues .)

Calcium and vitamin D supplementation may help bones heal that have become fractured due to bone thinning. ⁷ Calcium supplements may do a better job of strengthening bones when people have relatively high protein intake. ⁸ Heavy exercise causes increased calcium loss through sweat, and the the body does not compensate for this by reducing calcium loss in the urine. ⁹ The result can be a net calcium loss great enough so that it presents health concerns for menopausal women, already at risk for osteoporosis. One study found that use of an inexpensive calcium supplement (calcium carbonate), taken at a dose of 400 mg twice daily, is sufficient to offset this loss. ¹⁰ Calcium supplementation could, in theory, be useful for young girls as a way to "put calcium in the bank"—building up a supply for the future in order to prevent later osteoporosis. However, surprisingly, the benefits seen in studies have been modest to nonexistent, and this approach may only produce results when exercise is also increased. ¹¹ One study found that in calcium-deficient pregnant women, calcium supplements can improve the bones of their unborn children. ¹² Evidence suggests that the use of calcium combined with vitamin D can help protect against the bone loss caused by corticosteroid drugs, such as prednisone. A review of five studies covering a total of 274 participants reported that calcium and vitamin D supplementation significantly prevented bone loss in corticosteroid-treated individuals. ¹³ For example, in a 2-year, double-blind, placebo-controlled study that followed 65 individuals with rheumatoid arthritis taking low-dose corticosteroids, daily supplementation with 1,000 mg of calcium and 500 IU of vitamin D reversed steroid-induced bone loss, causing a net bone gain. ¹⁴ There is some evidence that essential fatty acids may enhance the effectiveness of calcium. In one study, 65 postmenopausal women were given calcium along with either placebo or a combination of omega-6 fatty acids (from evening primrose oil ) and omega-3 fatty acids (from fish oil ) for a period of 18 months. At the end of the study period, the group receiving essential fatty acids had higher bone density and fewer fractures than the placebo group. ¹⁵ However, a 12-month, double-blind trial of 42 postmenopausal women found no benefit. ¹⁶ The explanation for the discrepancy may lie in the differences between the women studied. The first study involved women living in nursing homes, while the second studied healthier women living on their own. The latter group of women may have been better nourished and already received enough essential fatty acids in their diet.

Premenstrual Syndrome (PMS)

According to a large and well-designed study published in a 1998 issue of American Journal of Obstetrics and Gynecology,calcium supplements are a simple and effective treatment for a wide variety of PMS symptoms. ¹⁷ In a double-blind, placebo-controlled study of 497 women, 1,200 mg daily of calcium as calcium carbonate reduced PMS symptoms by half over a period of three menstrual cycles. These symptoms included mood swings, headaches, food cravings, and bloating. These results corroborate earlier, smaller studies. ¹⁸

High Cholesterol

In a 12-month study of 223 postmenopausal women, use of calcium citrate at a dose of 1 g daily improved the ratio of HDL (“good”) cholesterol levels to LDL (“bad”) cholesterol levels. ¹⁹ The extent of this improvement was statistically significant (as compared to the placebo group), but not very large in practical terms. Similarly modest benefits were seen in a previous, smaller double-blind, placebo-controlled study. ²⁰ A third double-blind, placebo-controlled study failed to find any statistically significant effects. ²¹

Colon Cancer

Evidence from observational studies showed that a high calcium intake is associated with a reduced incidence of colon cancer , ²² but not all studies have found this association. ²³ Some but not all evidence from intervention trials supports these findings. ²⁴ A 4-year, double-blind, placebo-controlled study followed 832 individuals with a history of colon polyps. ²⁵ Participants received either 3 g daily of calcium carbonate or placebo. The calcium group experienced 24% fewer polyps overall than the placebo group. Since colon polyps are the precursor of most colon cancer, this finding strongly suggests benefit. Combing the results for two trials, involving a total of 1,346 subjects also with a history of polyps, researchers found that 1,200 mg or 2,000 mg of daily elemental calcium led to a significant reduction in polyp recurrence compared to placebo over a 3-4 year period. ²⁶ Another, large-sized study found that calcium carbonate at a dose of 1,200 mg daily may have a more pronounced effect on dangerous polyps than on benign ones. ²⁷ However, a gigantic (36,282 participant), very long-term (average 7 years) study of postmenopausal women failed to find that calcium carbonate supplements at a dose of 1,000 mg daily had any effect on the incidence of colon cancer. ²⁸ Given these conflicting results, if calcium supplementation does have an effect on colon cancer risk, it is probably small.

Hypertension

A very large randomized, placebo-controlled trial of over 36,000 postmenopausal women found daily supplementation with 1,000 mg of calcium plus 400 IU of vitamin D did not reduce or prevent hypertension during 7 years of follow-up. These results are possibly limited by non-study calcium use. ²⁹

Safety Issues

In general, it's safe to take up to 2,500 mg of calcium daily, although this is more than you need. ¹ Greatly excessive intake of calcium can cause numerous side effects, including dangerous or painful deposits of calcium within the body.

Note:If you have cancer, hyperparathyroidism, or sarcoidosis, you should take calcium only under a physician's supervision.

Some evidence hints that use of calcium supplements might slightly increase kidney stone risk. ² However, increased intake of calcium from fooddoes not seem to have this effect and could even help prevent stones. ³ One study found that if calcium supplements are taken with food, there is no increased risk. ⁴ Calcium citrate supplements may be particularly safe regarding kidney stones because the citrate portion of this supplement is used to treatkidney stones. ⁵ There is preliminary evidence that calcium supplementation in healthy, post-menopausal women may slightly increase the risk of cardiovascular events, such as myocardial infarction. However, it remains far from clear whether this possible risk outweighs the benefits of calcium supplementation in this population. ⁶ Large observational studies have found that, in men, higher intakes of calcium are associated with an increased risk of prostate cancer. ⁷ This seems to be the case whether the calcium comes from milk or from calcium supplements.

Calcium supplements combined with high doses of vitamin D might interfere with some of the effects of drugs in the calcium channel blocker family. ⁸ It is very important that you consult your physician before trying this combination.

Concerns have been raised that the aluminum in some antacids may not be good for you. ⁹ There is some evidence that calcium citrate supplements might increase the absorption of aluminum; ^{10 11 12 13} for this reason, it might not be a good idea to take calcium citrate at the same time of day as aluminum-containing antacids. Another option is to use different forms of calcium, or to avoid antacids containing aluminum.

When taken over the long term, thiazide diuretics tend to increase levels of calcium in the body by decreasing the amount excreted by the body. ^{14 15 16} It's not likely that this will cause a problem. Nonetheless, if you are using thiazide diuretics, you should consult with your physician on the proper doses of calcium and vitamin D for you.

Finally, calcium may interfere with the absorption of antibiotics in the tetracycline and fluoroquinolone families as well as thyroid hormone. ^{17 18 19 20 21 22} If you are taking any of these drugs, you should take your calcium supplements at least 2 hours before or after your medication dose.

Interactions You Should Know About

• You may need more calcium if you are taking:
  • Corticosteroids
  • Heparin
  • Isoniazid

• If you are taking aluminum hydroxide , you should take calcium citrate at least 2 hours apart to avoid increasing aluminum absorption.

• You may need more calcium if you are taking the following anticonvulsants:
  • Phenytoin (Dilantin)
  • Carbamazepine
  • Phenobarbital
  • Primidone
  • Note:It may be advisable to take your dose of anticonvulsant and your calcium supplement at least 2 hours apart because each interferes with the other's absorption.

• If you are taking the following medications, you should take your calcium supplement at least 2 hours before or after your dose of medication because calcium interferes with the absorption (and vice versa):
  • Antibiotics in the tetracycline or fluoroquinolone (Cipro, Floxin, Noroxin) families
  • Thyroid hormone

• Do not take extra calcium except on the advice of a physician if you are taking Thiazide diuretics.

• Do not take calcium together with high-dose vitamin D except on the advice of a physician if you are taking calcium channel blockers .

• You may need extra calcium if you are taking:
  • Iron [
  • Manganese
  • Zinc]
  • Chromium
  • Ideally, you should take calcium at a different time of day from these other minerals because it may interfere with their absorption.

• It may be advisable to wait 2 hours after taking calcium supplements to eat soy (or vice versa). A constituent of soy called phytic acid can interfere with the absorption of calcium.

• Taking supplemental calcium may be helpful if you are taking metformin.

Although there are some variations between recommendations issued by different groups, the official US and Canadian recommendations for daily intake of calcium are as follows:

• Infants
  • 0-6 months: 210 mg
  • 7-12 months: 270 mg

• Children
  • 1-3 years: 500 mg
  • 4-8 years: 800 mg

• Males and Females
  • 9-18 years: 1,300 mg
  • 19-50 years: 1,000 mg
  • 51 years and older: 1,200 mg

• Pregnant and Nursing Women
  • Under 19 years: 1,300 mg
  • 19 years and older: 1,000 mg

To absorb calcium, your body also needs an adequate level of vitamin D (for more information, see the article on Vitamin D ).

Various medications may impair calcium absorption or metabolism, either directly or through effects on vitamin D. People who use these may benefit by taking extra calcium and vitamin D. Implicated medications include corticosteroids , ^{1 2} heparin , ^{3 4} isoniazid , ^{5 6} and anticonvulsants . ^{7 8 9 10 11 12} Note:Calcium carbonate might interfere with the effects of anticonvulsant drugs, and for that reason should not be taken at the same time of day. ¹³ Milk, cheese, and other dairy products are excellent sources of calcium. Other good sources include orange juice or soy milk fortified with calcium, fish canned with its bones (such as sardines), dark green vegetables, nuts and seeds, and calcium-processed tofu.

Many forms of calcium supplements are available on the market, each with its own advantages and disadvantages.

Naturally Derived Forms of Calcium

These forms of calcium come from bone, shells, or the earth: bonemeal, oyster shell, and dolomite. Animals concentrate calcium in their shells, and calcium is found in minerals in the earth. These forms of calcium are economical, and you can get as much as 500 mg to 600 mg in one tablet. However, there are concerns that the natural forms of calcium supplements may contain significant amounts of lead. ¹⁴ The level of contamination has decreased in recent years, but still may present a health risk. ¹⁵ Calcium supplements rarely list the lead content of their source, although they should. The lead concentration should always be less than 2 parts per million.

Refined Calcium Carbonate

This is the most common commercial calcium supplement, and it is also used as a common antacid. Calcium carbonate is one of the least expensive forms of calcium, but it can cause constipation and bloating, and it may not be well absorbed by people with reduced levels of stomach acid. Taking it with meals improves absorption because stomach acid is released to digest the food. ¹⁶ (See the section, Chelated Calcium, below.)

Chelated Calcium

Chelated calcium is calcium bound to an organic acid (citrate, citrate malate, lactate, gluconate, aspartate, or orotate). The chelated forms of calcium offer some significant advantages and disadvantages compared with calcium carbonate.

Certain forms of chelated calcium (calcium citrate and calcium citrate malate) are widely thought to be significantly better absorbed and more effective for osteoporosis treatment than calcium carbonate. However, while some studies support this belief, ¹⁷ others do not. ¹⁸ The discrepancy may be due to the particular calcium carbonate products used; some calcium carbonate formulations may dissolve better than others.

One study found that calcium citrate malate in orange juice is markedly better absorbed than tricalcium phosphate/calcium lactate in orange juice. ¹⁹ A form of calcium called active absorbable algal calcium (AAACa) has also been promoted as superior to calcium carbonate, but the study upon which claims of benefit are founded actually used quite questionable statistical methods (technically, post-hoc subgroup analysis). ²⁰ Chelated calcium is much more expensive and bulkier than calcium carbonate. In other words, you have to take larger pills, and more of them, to get enough calcium. It is not at all uncommon to need to take five or six large capsules daily to supply the necessary amount, a quantity some people may find troublesome.

w

Unlike some supplements, calcium is not taken at extra high doses for special therapeutic benefit. Rather, for all its uses, it should be taken in the amounts listed under Requirements/Sources, along with the recommended level of vitamin D. (See the article on vitamin D for proper dosage amounts.)

Calcium absorption studies have found evidence that your body can't absorb more than 500 mg of calcium at one time. ¹ Therefore, it is most efficient to take your total daily calcium in two or more doses.

Use of prebiotics known as "inulin fructans" may improve calcium absorption. ² It isn't possible to put all the calcium you need in a single multivitamin/mineral tablet, so this is one supplement that should be taken on its own. Furthermore, if taken at the same time, calcium may interfere with the absorption of chromium and manganese . ³ This means that it is best to take your multivitamin and mineral pill at a separate time from your calcium supplement.

Although the calcium present in some antacids or supplements may alter the absorption of magnesium , this effect apparently has no significant influence on overall magnesium status. ⁴ Calcium may also interfere with iron absorption, ^{5 6} but the effect may be too slight to cause a problem. Some studies show that calcium may decrease zinc absorption when the two are taken together as supplements; however, studies have found that, in the presence of meals, zinc levels may be unaffected by increases of either dietary or supplemental calcium. ^{7 8 9 10 11 12}

According to most, though not all studies, use of calcium (especially in the form of calcium citrate) combined with vitamin D may modestly slow the bone loss that leads to osteoporosis . ¹ A rather surprising potential use of calcium came to light when a large, well-designed study found that calcium is an effective treatment for premenstrual syndrome (PMS). ² Calcium supplementation reduced all major symptoms, including headache, food cravings, moodiness, and fluid retention. It is at least remotely possible that there may be a connection between these two uses of calcium: weak evidence hints that PMS might be an early sign of future osteoporosis. ³ One small but carefully conducted study suggests that getting enough calcium may help control symptoms of menstrual pain . ⁴ Some, but not all, observational and intervention studies have found evidence that calcium supplementation may reduce the risk of colon cancer . ⁵ Risk reduction might continue for years after calcium supplements are stopped. ⁶ However, calcium supplements might increase risk of prostate cancer in men, as discussed in the Safety Issues section. For menopausal women, calcium supplementation, especially with vitamin D added, may reduce cancer risk in general. ⁷ Individuals who are deficient in calcium may be at greater risk of developing high blood pressure . ⁸ Among individuals who already have hypertension, increased intake of calcium might slightly decrease blood pressure, according to some, but not all, studies. ⁹ Weak evidence hints that use of calcium by pregnant mothers might reduce risk of hypertension in their children. ¹⁰ Calcium supplements might slightly improve the cholesterol profile. ¹¹ Calcium supplementation has also been tried as a treatment to prevent preeclampsia in pregnant women. While the evidence from studies is conflicting, ¹² calcium supplementation might offer at least a minimal benefit.

The drug metformin , used for diabetes, interferes with the absorption of vitamin B 12 . Interestingly, calcium supplements may reverse this, allowing the B 12 to be absorbed normally. ¹³ Rapid weight loss in overweight postmenopausal women appears to slightly accelerate bone loss. ¹⁴ For this reason, it may make sense to take calcium and vitamin D supplements when deliberately losing weight. It has been additionally suggested that calcium supplements, or high-calcium diets, may directly enhance weight loss, but current evidence is more negative than positive. ¹⁵ Finally, calcium is also sometimes recommended for attention deficit disorder , migraine headaches , and periodontal disease , but there is as yet no meaningful evidence that it is effective for these conditions.

It is important to note that despite the benefits of calcium supplementation for certain conditions, a large, placebo-controlled trial involving over 36,000 post-menopausal women found that daily supplements of 1,000 mg of calcium carbonate combined with 400 IU of vitamin D(3) for an average of seven years did not significantly reduce death rates from all causes.196

Calcium is the most abundant mineral in the body, making up nearly 2% of total body weight. More than 99% of the calcium in your body is found in your bones, but the other 1% is perhaps just as important for good health. Many enzymes depend on calcium in order to work properly, as do your nerves, heart, and blood-clotting mechanisms.

To build bone, you need to have enough calcium in your diet. But in spite of calcium-fortified orange juice and the best efforts of the dairy industry, most Americans are calcium deficient. ¹ Calcium supplements are a simple way to make sure you're getting enough of this important mineral.

One of the most important uses of calcium is to help prevent and treat osteoporosis, the progressive loss of bone mass to which menopausal women are especially vulnerable. Calcium works best when combined with vitamin D.

Other meaningful evidence suggests that calcium may have an additional important use: reducing PMS symptoms.

Although there are some variations between recommendations issued by different groups, the official US and Canadian recommendations for daily intake of calcium are as follows:

• Infants
  • 0-6 months: 210 mg
  • 7-12 months: 270 mg

• Children
  • 1-3 years: 500 mg
  • 4-8 years: 800 mg

• Males and Females
  • 9-18 years: 1,300 mg
  • 19-50 years: 1,000 mg
  • 51 years and older: 1,200 mg

• Pregnant and Nursing Women
  • Under 19 years: 1,300 mg
  • 19 years and older: 1,000 mg

To absorb calcium, your body also needs an adequate level of vitamin D (for more information, see the article on Vitamin D ).

Various medications may impair calcium absorption or metabolism, either directly or through effects on vitamin D. People who use these may benefit by taking extra calcium and vitamin D. Implicated medications include corticosteroids , ^{1 2} heparin , ^{3 4} isoniazid , ^{5 6} and anticonvulsants . ^{7 8 9 10 11 12} Note:Calcium carbonate might interfere with the effects of anticonvulsant drugs, and for that reason should not be taken at the same time of day. ¹³ Milk, cheese, and other dairy products are excellent sources of calcium. Other good sources include orange juice or soy milk fortified with calcium, fish canned with its bones (such as sardines), dark green vegetables, nuts and seeds, and calcium-processed tofu.

Many forms of calcium supplements are available on the market, each with its own advantages and disadvantages.

Naturally Derived Forms of Calcium

These forms of calcium come from bone, shells, or the earth: bonemeal, oyster shell, and dolomite. Animals concentrate calcium in their shells, and calcium is found in minerals in the earth. These forms of calcium are economical, and you can get as much as 500 mg to 600 mg in one tablet. However, there are concerns that the natural forms of calcium supplements may contain significant amounts of lead. ¹⁴ The level of contamination has decreased in recent years, but still may present a health risk. ¹⁵ Calcium supplements rarely list the lead content of their source, although they should. The lead concentration should always be less than 2 parts per million.

Refined Calcium Carbonate

This is the most common commercial calcium supplement, and it is also used as a common antacid. Calcium carbonate is one of the least expensive forms of calcium, but it can cause constipation and bloating, and it may not be well absorbed by people with reduced levels of stomach acid. Taking it with meals improves absorption because stomach acid is released to digest the food. ¹⁶ (See the section, Chelated Calcium, below.)

Chelated Calcium

Chelated calcium is calcium bound to an organic acid (citrate, citrate malate, lactate, gluconate, aspartate, or orotate). The chelated forms of calcium offer some significant advantages and disadvantages compared with calcium carbonate.

Certain forms of chelated calcium (calcium citrate and calcium citrate malate) are widely thought to be significantly better absorbed and more effective for osteoporosis treatment than calcium carbonate. However, while some studies support this belief, ¹⁷ others do not. ¹⁸ The discrepancy may be due to the particular calcium carbonate products used; some calcium carbonate formulations may dissolve better than others.

One study found that calcium citrate malate in orange juice is markedly better absorbed than tricalcium phosphate/calcium lactate in orange juice. ¹⁹ A form of calcium called active absorbable algal calcium (AAACa) has also been promoted as superior to calcium carbonate, but the study upon which claims of benefit are founded actually used quite questionable statistical methods (technically, post-hoc subgroup analysis). ²⁰ Chelated calcium is much more expensive and bulkier than calcium carbonate. In other words, you have to take larger pills, and more of them, to get enough calcium. It is not at all uncommon to need to take five or six large capsules daily to supply the necessary amount, a quantity some people may find troublesome.

Osteoporosis

A number of double-blind, placebo-controlled studies indicate that calcium supplements (especially as calcium citrate, and taken with vitamin D) are slightly helpful in preventing and slowing down bone loss in postmenopausal women. ¹ Contrary to some reports, milk does appear to be a useful source of calcium for this purpose. ² However, the effect of calcium supplementation in any form is relatively mild and may not be strong enough to reduce the rate of osteoporotic fractures. Note that use of calcium and vitamin Dmust be continual. Any improvements in bone density rapidly disappear once the supplements are stopped. ³ A large study of over 3,000 postmenopausal women aged 65-71 years found that three years of daily supplementation with calcium and vitamin D was not associated with a significant reduction in the incidence of fractures. ⁴ Calcium carbonate may not be effective. ⁵ One study found benefits for male seniors using a calcium and vitamin D-fortified milk product. ⁶ (See, however, possible increased risk of prostate cancer discussed in Safety Issues .)

Calcium and vitamin D supplementation may help bones heal that have become fractured due to bone thinning. ⁷ Calcium supplements may do a better job of strengthening bones when people have relatively high protein intake. ⁸ Heavy exercise causes increased calcium loss through sweat, and the the body does not compensate for this by reducing calcium loss in the urine. ⁹ The result can be a net calcium loss great enough so that it presents health concerns for menopausal women, already at risk for osteoporosis. One study found that use of an inexpensive calcium supplement (calcium carbonate), taken at a dose of 400 mg twice daily, is sufficient to offset this loss. ¹⁰ Calcium supplementation could, in theory, be useful for young girls as a way to "put calcium in the bank"—building up a supply for the future in order to prevent later osteoporosis. However, surprisingly, the benefits seen in studies have been modest to nonexistent, and this approach may only produce results when exercise is also increased. ¹¹ One study found that in calcium-deficient pregnant women, calcium supplements can improve the bones of their unborn children. ¹² Evidence suggests that the use of calcium combined with vitamin D can help protect against the bone loss caused by corticosteroid drugs, such as prednisone. A review of five studies covering a total of 274 participants reported that calcium and vitamin D supplementation significantly prevented bone loss in corticosteroid-treated individuals. ¹³ For example, in a 2-year, double-blind, placebo-controlled study that followed 65 individuals with rheumatoid arthritis taking low-dose corticosteroids, daily supplementation with 1,000 mg of calcium and 500 IU of vitamin D reversed steroid-induced bone loss, causing a net bone gain. ¹⁴ There is some evidence that essential fatty acids may enhance the effectiveness of calcium. In one study, 65 postmenopausal women were given calcium along with either placebo or a combination of omega-6 fatty acids (from evening primrose oil ) and omega-3 fatty acids (from fish oil ) for a period of 18 months. At the end of the study period, the group receiving essential fatty acids had higher bone density and fewer fractures than the placebo group. ¹⁵ However, a 12-month, double-blind trial of 42 postmenopausal women found no benefit. ¹⁶ The explanation for the discrepancy may lie in the differences between the women studied. The first study involved women living in nursing homes, while the second studied healthier women living on their own. The latter group of women may have been better nourished and already received enough essential fatty acids in their diet.

Premenstrual Syndrome (PMS)

According to a large and well-designed study published in a 1998 issue of American Journal of Obstetrics and Gynecology,calcium supplements are a simple and effective treatment for a wide variety of PMS symptoms. ¹⁷ In a double-blind, placebo-controlled study of 497 women, 1,200 mg daily of calcium as calcium carbonate reduced PMS symptoms by half over a period of three menstrual cycles. These symptoms included mood swings, headaches, food cravings, and bloating. These results corroborate earlier, smaller studies. ¹⁸

High Cholesterol

In a 12-month study of 223 postmenopausal women, use of calcium citrate at a dose of 1 g daily improved the ratio of HDL (“good”) cholesterol levels to LDL (“bad”) cholesterol levels. ¹⁹ The extent of this improvement was statistically significant (as compared to the placebo group), but not very large in practical terms. Similarly modest benefits were seen in a previous, smaller double-blind, placebo-controlled study. ²⁰ A third double-blind, placebo-controlled study failed to find any statistically significant effects. ²¹

Colon Cancer

Evidence from observational studies showed that a high calcium intake is associated with a reduced incidence of colon cancer , ²² but not all studies have found this association. ²³ Some but not all evidence from intervention trials supports these findings. ²⁴ A 4-year, double-blind, placebo-controlled study followed 832 individuals with a history of colon polyps. ²⁵ Participants received either 3 g daily of calcium carbonate or placebo. The calcium group experienced 24% fewer polyps overall than the placebo group. Since colon polyps are the precursor of most colon cancer, this finding strongly suggests benefit. Combing the results for two trials, involving a total of 1,346 subjects also with a history of polyps, researchers found that 1,200 mg or 2,000 mg of daily elemental calcium led to a significant reduction in polyp recurrence compared to placebo over a 3-4 year period. ²⁶ Another, large-sized study found that calcium carbonate at a dose of 1,200 mg daily may have a more pronounced effect on dangerous polyps than on benign ones. ²⁷ However, a gigantic (36,282 participant), very long-term (average 7 years) study of postmenopausal women failed to find that calcium carbonate supplements at a dose of 1,000 mg daily had any effect on the incidence of colon cancer. ²⁸ Given these conflicting results, if calcium supplementation does have an effect on colon cancer risk, it is probably small.

Hypertension

A very large randomized, placebo-controlled trial of over 36,000 postmenopausal women found daily supplementation with 1,000 mg of calcium plus 400 IU of vitamin D did not reduce or prevent hypertension during 7 years of follow-up. These results are possibly limited by non-study calcium use. ²⁹

According to most, though not all studies, use of calcium (especially in the form of calcium citrate) combined with vitamin D may modestly slow the bone loss that leads to osteoporosis . ¹ A rather surprising potential use of calcium came to light when a large, well-designed study found that calcium is an effective treatment for premenstrual syndrome (PMS). ² Calcium supplementation reduced all major symptoms, including headache, food cravings, moodiness, and fluid retention. It is at least remotely possible that there may be a connection between these two uses of calcium: weak evidence hints that PMS might be an early sign of future osteoporosis. ³ One small but carefully conducted study suggests that getting enough calcium may help control symptoms of menstrual pain . ⁴ Some, but not all, observational and intervention studies have found evidence that calcium supplementation may reduce the risk of colon cancer . ⁵ Risk reduction might continue for years after calcium supplements are stopped. ⁶ However, calcium supplements might increase risk of prostate cancer in men, as discussed in the Safety Issues section. For menopausal women, calcium supplementation, especially with vitamin D added, may reduce cancer risk in general. ⁷ Individuals who are deficient in calcium may be at greater risk of developing high blood pressure . ⁸ Among individuals who already have hypertension, increased intake of calcium might slightly decrease blood pressure, according to some, but not all, studies. ⁹ Weak evidence hints that use of calcium by pregnant mothers might reduce risk of hypertension in their children. ¹⁰ Calcium supplements might slightly improve the cholesterol profile. ¹¹ Calcium supplementation has also been tried as a treatment to prevent preeclampsia in pregnant women. While the evidence from studies is conflicting, ¹² calcium supplementation might offer at least a minimal benefit.

The drug metformin , used for diabetes, interferes with the absorption of vitamin B 12 . Interestingly, calcium supplements may reverse this, allowing the B 12 to be absorbed normally. ¹³ Rapid weight loss in overweight postmenopausal women appears to slightly accelerate bone loss. ¹⁴ For this reason, it may make sense to take calcium and vitamin D supplements when deliberately losing weight. It has been additionally suggested that calcium supplements, or high-calcium diets, may directly enhance weight loss, but current evidence is more negative than positive. ¹⁵ Finally, calcium is also sometimes recommended for attention deficit disorder , migraine headaches , and periodontal disease , but there is as yet no meaningful evidence that it is effective for these conditions.

It is important to note that despite the benefits of calcium supplementation for certain conditions, a large, placebo-controlled trial involving over 36,000 post-menopausal women found that daily supplements of 1,000 mg of calcium carbonate combined with 400 IU of vitamin D(3) for an average of seven years did not significantly reduce death rates from all causes.196

Safety Issues

In general, it's safe to take up to 2,500 mg of calcium daily, although this is more than you need. ¹ Greatly excessive intake of calcium can cause numerous side effects, including dangerous or painful deposits of calcium within the body.

Note:If you have cancer, hyperparathyroidism, or sarcoidosis, you should take calcium only under a physician's supervision.

Some evidence hints that use of calcium supplements might slightly increase kidney stone risk. ² However, increased intake of calcium from fooddoes not seem to have this effect and could even help prevent stones. ³ One study found that if calcium supplements are taken with food, there is no increased risk. ⁴ Calcium citrate supplements may be particularly safe regarding kidney stones because the citrate portion of this supplement is used to treatkidney stones. ⁵ There is preliminary evidence that calcium supplementation in healthy, post-menopausal women may slightly increase the risk of cardiovascular events, such as myocardial infarction. However, it remains far from clear whether this possible risk outweighs the benefits of calcium supplementation in this population. ⁶ Large observational studies have found that, in men, higher intakes of calcium are associated with an increased risk of prostate cancer. ⁷ This seems to be the case whether the calcium comes from milk or from calcium supplements.

Calcium supplements combined with high doses of vitamin D might interfere with some of the effects of drugs in the calcium channel blocker family. ⁸ It is very important that you consult your physician before trying this combination.

Concerns have been raised that the aluminum in some antacids may not be good for you. ⁹ There is some evidence that calcium citrate supplements might increase the absorption of aluminum; ^{10 11 12 13} for this reason, it might not be a good idea to take calcium citrate at the same time of day as aluminum-containing antacids. Another option is to use different forms of calcium, or to avoid antacids containing aluminum.

When taken over the long term, thiazide diuretics tend to increase levels of calcium in the body by decreasing the amount excreted by the body. ^{14 15 16} It's not likely that this will cause a problem. Nonetheless, if you are using thiazide diuretics, you should consult with your physician on the proper doses of calcium and vitamin D for you.

Finally, calcium may interfere with the absorption of antibiotics in the tetracycline and fluoroquinolone families as well as thyroid hormone. ^{17 18 19 20 21 22} If you are taking any of these drugs, you should take your calcium supplements at least 2 hours before or after your medication dose.

Interactions You Should Know About

• You may need more calcium if you are taking:
  • Corticosteroids
  • Heparin
  • Isoniazid

• If you are taking aluminum hydroxide , you should take calcium citrate at least 2 hours apart to avoid increasing aluminum absorption.

• You may need more calcium if you are taking the following anticonvulsants:
  • Phenytoin (Dilantin)
  • Carbamazepine
  • Phenobarbital
  • Primidone
  • Note:It may be advisable to take your dose of anticonvulsant and your calcium supplement at least 2 hours apart because each interferes with the other's absorption.

• If you are taking the following medications, you should take your calcium supplement at least 2 hours before or after your dose of medication because calcium interferes with the absorption (and vice versa):
  • Antibiotics in the tetracycline or fluoroquinolone (Cipro, Floxin, Noroxin) families
  • Thyroid hormone

• Do not take extra calcium except on the advice of a physician if you are taking Thiazide diuretics.

• Do not take calcium together with high-dose vitamin D except on the advice of a physician if you are taking calcium channel blockers .

• You may need extra calcium if you are taking:
  • Iron
  • Manganese
  • Zinc
  • Chromium
  • Ideally, you should take calcium at a different time of day from these other minerals because it may interfere with their absorption.

• It may be advisable to wait 2 hours after taking calcium supplements to eat soy (or vice versa). A constituent of soy called phytic acid can interfere with the absorption of calcium.

• Taking supplemental calcium may be helpful if you are taking metformin.

Unlike some supplements, calcium is not taken at extra high doses for special therapeutic benefit. Rather, for all its uses, it should be taken in the amounts listed under Requirements/Sources, along with the recommended level of vitamin D. (See the article on vitamin D for proper dosage amounts.)

Calcium absorption studies have found evidence that your body can't absorb more than 500 mg of calcium at one time. ¹ Therefore, it is most efficient to take your total daily calcium in two or more doses.

Use of prebiotics known as "inulin fructans" may improve calcium absorption. ² It isn't possible to put all the calcium you need in a single multivitamin/mineral tablet, so this is one supplement that should be taken on its own. Furthermore, if taken at the same time, calcium may interfere with the absorption of chromium and manganese . ³ This means that it is best to take your multivitamin and mineral pill at a separate time from your calcium supplement.

Although the calcium present in some antacids or supplements may alter the absorption of magnesium , this effect apparently has no significant influence on overall magnesium status. ⁴ Calcium may also interfere with iron absorption, ^{5 6} but the effect may be too slight to cause a problem. Some studies show that calcium may decrease zinc absorption when the two are taken together as supplements; however, studies have found that, in the presence of meals, zinc levels may be unaffected by increases of either dietary or supplemental calcium. ^{7 8 9 10 11 12}