Zinc:
What is it?

Zinc:
How is it Used?


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Zinc Overview

Overview

Zinc is an important element that is found in every cell in the body. More than 300 enzymes in the body need zinc in order to function properly. Although the amount of zinc we need in our daily diet is tiny, it's very important that we get it. However, the evidence suggests that many of us do not get enough. Mild zinc deficiency seems to be fairly common, and for this reason taking a zinc supplement at nutritional doses may be a good idea.

However, taking too much zinc isn’t a good idea—it can cause toxicity. In this article, we discuss the possible uses of zinc at various doses.

Requirements/Sources

The official US recommendations for daily intake of zinc are as follows:

  • Infants
  • 0-6 months: 2 mg
  • 7-12 months: 3 mg
  • Children
  • 1-3 years: 3 mg
  • 4-8 years: 5 mg
  • Males
  • 9-13 years: 8 mg
  • 14 years and older: 11 mg
  • Females
  • 9-13 years: 8 mg
  • 14-18 years: 9 mg
  • 19 years and older: 8 mg
  • Pregnant Women
  • 18 years and younger: 13 mg
  • 19 years and older: 11 mg
  • Nursing Women
  • 18 years and younger: 14 mg
  • 19 years and older: 12 mg

The average diet in the developed world may provide insufficient zinc, especially in women, adolescents, infants, and the elderly. ^[1] Thus, it may be a wise idea to increase your intake of zinc on general principles.

Various drugs may tend to reduce levels zinc in the body by inhibiting its absorption or increasing its excretion. These include captopril and possibly other ACE inhibitors , oral contraceptives , thiazide diuretics , ^[6] and drugs which reduce stomach acid (including H 2 blockers and proton pump inhibitors ). Certain nutrients may also inhibit zinc absorption, including calcium , soy , manganese , copper , and iron . ^[14] ^[15] ^[16] ^[17] ^[18] ^[19] ^[20] ^[21] ^[22] ^[23] ^[24] ^[25] ^[26] ^[27] ^[28] ^[29] Contrary to previous reports, folate is not likely to have this effect. ^[31] Oysters have a very high zinc content—one oyster provides at least the full daily dose of zinc (about 8 mg to15 mg zinc). Besides oysters, other types of shellfish, along with poultry and meat (especially organ meats), are high in zinc, providing 1 mg to 8 mg of zinc per serving. Whole grains, nuts, and seeds provide smaller amounts of zinc, ranging from 0.2 mg to about 3 mg per serving, and the zinc from them is not as absorbable. Breakfast cereals and nutrition bars are often fortified with substantial amounts of zinc.

Zinc can also be taken as a nutritional supplement, in one of many forms. Zinc citrate, zinc acetate, or zinc picolinate may be the best absorbed, although zinc sulfate is less expensive. When you purchase a supplement, you should be aware of the difference between the milligrams of actual zinc that the product contains (so-called elemental zinc) and the total milligrams of the zinc product, which includes the weight of the sulfate, picolinate, and so forth. All dosages given in this article refer to elemental zinc (unless otherwise stated).

Therapeutic Dosages

For most purposes, zinc should simply be taken at the recommended daily requirements listed previously.

Some evidence suggests that 30 mg of zinc daily may be helpful for acne. This is a safe dose for most people. However, in most studies of zinc for acne, a much higher dose was used: 90 mg daily or more. Doses this high should only be used under physician supervision (see Safety Issues ). Potentially dangerous doses of zinc have also been recommended for sickle-cell anemia, macular degeneration, and rheumatoid arthritis.

For best absorption, zinc supplements should not be taken at the same time as high-fiber foods. ^[1] However, many high-fiber foods provide zinc in themselves.

Zinc gluconate may be slightly better absorbed than zinc oxide. ^[2] When taking zinc long-term it is advisable to take 1 mg to 3 mg of copper daily as well, because zinc supplements can cause copper deficiency. ^[4] Zinc may also interfere with magnesium ^[6] and iron ^[8] absorption.

Zinc is used topically in lozenge or nasal gel form for the treatment of colds. When using zinc this way, the purpose is not to increase zinc levels in your body, but to interfere with the action of viruses in the back of your throat or in the nose. It appears that of the common forms of zinc, only zinc gluconate and zinc acetate have the required antiviral properties. ^[9] Certain sweeteners and flavorings used in lozenges can block zinc's antiviral action. Dextrose, sucrose, mannitol, and sorbitol appear to be fine, but citric acid and tartaric acid are not. The information on glycine as a flavoring agent is a bit equivocal.

Note: When using zinc nasal gel products, do not deeply inhale, as this may cause severe pain. Rather, simply squeeze the gel into the nose, according to the directions.

What Is the Scientific Evidence for Zinc?

#Colds

Use of lozenges containing zinc gluconate or zinc acetate have shown somewhat inconsistent but generally positive results for reducing the severity and duration of the common cold. For example, in a double-blind trial, 100 people who were experiencing the early symptoms of a cold were given a lozenge that either contained 13.3 mg of zinc from zinc gluconate or was just a placebo. ^[1] Participants took the lozenges several times daily until their cold symptoms subsided. The results were impressive. Coughing disappeared within 2.2 days in the treated group versus 4 days in the placebo group. Sore throat disappeared after 1 day versus 3 days in the placebo group, nasal drainage in 4 days (versus 7 days), and headache in 2 days (versus 3 days).

Positive results have also been seen in double-blind studies of zinc acetate. ^[2] Not all studies have shown such positive results. ^[3] However, the overall results appear to be favorable. ^[4] It has been suggested that the exact formulation of the zinc lozenge plays a significant role in its effectiveness. ^[5] According to this view, certain flavoring agents, such as citric acid and tartaric acid, might prevent zinc from inhibiting viruses. In addition, chemical forms of zinc other than zinc gluconate or zinc acetate might be ineffective. Zinc sulfate in particular might not work. ^[6] Along the same lines, sweeteners such as sorbitol, sucrose, dextrose, and mannitol are said to be fine, while glycine has been discussed in an equivocal manner.

Use of zinc in the nose is somewhat more controversial. ^[7] In addition to showing inconsistent results in studies, use of zinc nasal gel can cause pain and possibly loss of sense of smell. ( See Safety Issues .)

For example, in a double-blind, placebo-controlled trial of a widely available zinc nasal gel product , 213 people with a newly starting cold used one squirt of zinc gluconate gel or placebo gel in each nostril every 4 hours while awake. ^[8] The results were significant: treated participants stayed sick an average of 2.3 days, while those receiving placebo were sick for an average of 9 days, a 75% reduction in the duration of symptoms. Somewhat more modest, but still significant relative benefits were seen with zinc nasal gel in a double-blind, placebo-controlled study of 80 people with colds. ^[9] However, another study, this one involving 77 people, failed to find benefit even with near constant saturation of the nasal passages with zinc gluconate nasal spray. ^[10] Furthermore, a study of 91 people using the standard commercially available nasal spray failed to find benefit. ^[11] Yet another double-blind, placebo-controlled trial, this one enrolling 185 individuals, failed to find benefit with zinc nasal spray. ^[12] However, this study used a much lower amount of zinc—50 times lower—per squirt of spray than was used in the studies just described.

Besides using zinc to directly interfere with viruses, supplementation at nutritional dosages may also help reduce the frequency of colds by generally enhancing immunity .

Chronic zinc deficiency is known to weaken the immune system, ^[14] A 1-year, double-blind study of 50 nursing home residents found that zinc supplements as compared to placebo reduced rates of infection. ^[15] Additionally, in a 2-year study of nursing home residents, participants given zinc and selenium developed illnesses less frequently than those given placebo. ^[16] Numerous studies in developing countries have also found benefit. For example, a 6-month, double-blind, placebo-controlled study of 609 preschool children in India found that zinc supplements reduced the rate of respiratory infections by 45%. ^[17] In addition, more than 10 other studies performed in developing countries have also found that zinc supplements were helpful for preventing respiratory and other infections in children, and that zinc might reduce symptom severity. ^[18]

#Cold Sores

Cold sores are infections caused by the herpes virus. One study suggests that topical zinc may be helpful. In this trial, 46 individuals with cold sores were treated with a zinc oxide cream or placebo every 2 hours until cold sores resolved. ^[19] The results showed that individuals using the cream experienced a reduction in severity of symptoms and a shorter time to full recovery.

Zinc is thought to interfere with the ability of the herpes virus to reproduce itself. As with colds, the formulation of zinc must be properly designed to release active zinc ions. This study used a special zinc oxide and glycine formulation.

Some participants in this study experienced burning and inflammation caused by the zinc itself, but this seldom caused a serious problem.

#Macular Degeneration

Macular degeneration is one of the most common causes of vision loss in the elderly.

A double-blind, placebo-controlled trial evaluated the effects of zinc with or without antioxidants on the progression of macular degeneration in 3,640 individuals in the early stage of the disease. ^[21] Participants were randomly assigned to receive one of the following: antioxidants ( vitamin C 500 mg, vitamin E 400 IU, and beta-carotene 15 mg), or zinc (80 mg) and copper (2 mg), antioxidants plus zinc, or placebo. (Copper was administered along with zinc to prevent zinc-induced copper deficiency.)

The results suggest that zinc (alone or, even better, with antioxidants) significantly slowed the progression of the disease.

Previous studies of zinc for macular degeneration found mixed results, but they were much smaller. ^[27] There is also some evidence that making sure to get your dietary requirement of zinc on a daily basis over many years might reduce the risk of developing macular degeneration later in life. ^[28] Keep in mind that the dosages of zinc used in most of these studies are rather high, and should be used only under a physician's supervision.

#Attention Deficit Hyperactivity Disorder

Zinc has shown some promise for treatment of attention deficit hyperactivity disorder (ADHD). In a large (approximately 400-participant), double-blind, placebo-controlled study, use of zinc at a dose of 40 mg daily produced statistically significant benefits as compared to placebo among children not using any other treatment. ^[30] This dose of zinc, while higher than nutritional needs, should be safe. However, the benefits seen were quite modest: about 28% of the participants given zinc showed improvement as compared to 20% in the placebo group.

Another, much smaller double-blind, placebo-controlled study evaluated whether zinc at 15 mg per day could enhance the effect of Ritalin. ^[31] Again, modest benefits were seen.

Finally, extremely weak evidence hints that zinc might enhance the effectiveness of evening primrose oil for ADHD. ^[33]

#Acne

Studies suggest that people with acne have lower-than-normal levels of zinc in their bodies. ^[34] ^[35] This fact alone does not prove that taking zinc supplements will help acne, but several small double-blind studies involving a total of more than 300 people have found generally positive results.

In one of these studies, 54 people were given either placebo or 135 mg of zinc (as zinc sulfate) daily. Zinc produced slight, but measurable benefits. ^[36] Similar results have been seen in other studies using 90 mg to 135 mg of zinc daily. ^[37] ^[38] ^[39] Some evidence suggests that a lower and safer dose, 30 mg daily, may offer some benefits. ^[40] In some studies, however, no benefits were seen. ^[41] Two studies have compared zinc against a standard treatment for acne, the antibiotic tetracycline. One study found that zinc was as effective as tetracycline taken at 250 mg daily, ^[42] but another found the antibiotic far more effective when taken at 500 mg daily. ^[43] Keep in mind that the dosages of zinc used in most of these studies are rather high; case reports indicate that people have made themselves extremely ill by taking zinc in hopes of treating their acne symptoms. ^[44] Doses of zinc higher than the recommended safe levels (see Safety Issues ) should be used only under a physician's supervision.

#Sickle-cell Disease

Children with sickle cell disease often do not grow normally. There is some evidence that people with sickle cell disease are more likely than others to be deficient in zinc. ^[46] Since zinc deficiency can also cause growth retardation, zinc supplementation at nutritional doses has been suggested for children with sickle cell disease. In a placebo-controlled study, 42 children (ages 4 to 10) with sickle cell disease were given either zinc supplements (10 mg of zinc daily) or placebo for a period of 1 year. ^[47] Results showed that by the end of the study, the participants given zinc showed enhanced growth compared to those given placebo. Curiously, researchers did not find any solid connection between the severity of zinc deficiency and the extent of response to treatment.

Zinc is thought to have a stabilizing effect on the cell membrane of red blood cells in people with sickle cell disease. For this reason, it has been tried as an aid for preventing sickle cell crisis. In a double-blind, placebo-controlled study of 145 people with sickle cell disease conducted in India, participants received either placebo or about 50 mg of zinc 3 times daily. ^[48] During 18 months of treatment, the zinc-treated subjects had an average of 2.5 crises, compared to 5.3 for the placebo group. However, zinc didn't seem to reduce the severity of a crisis, as measured by the number of days spent in the hospital for each crisis.

Sickle cell disease can also cause skin ulcers (nonhealing sores). In a 12-week, placebo-controlled trial, use of zinc at 88 mg 3 times per day for 12 weeks enhanced the rate of ulcer healing. ^[49]

Warning: The high dosages of zinc used in the last two studies can cause dangerous toxicity and should be taken (if at all) only under the supervision of a doctor. The nutritional dose described in the first study, however, is safe. (See Safety Issues .)

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