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Vitamin C
What is it? Overview Usage Side Effects and Warnings

Vitamin C Overview

Written by FoundHealth.

Although most animals can make vitamin C from scratch, humans have lost the ability over the course of evolution. We must get it from food, chiefly fresh fruits and vegetables. One of this vitamin's main functions is helping the body manufacture collagen, a key protein in our connective tissues, cartilage, and tendons.

From ancient times through the early nineteenth century, sailors and others deprived of fresh fruits and vegetables developed a disease called scurvy. Scurvy involves so-called scorbutic symptoms, which include nonhealing wounds, bleeding gums, bruising, and overall weakness. Now we know that scurvy is nothing more than vitamin C deficiency.

Scurvy was successfully treated with citrus fruit during the mid-1700s. In 1928, when Albert Szent-Gyorgyi isolated the active ingredient, he called it the anti-scorbutic principle, or ascorbic acid. This, of course, is vitamin C.

Vitamin C is a powerful antioxidant that neutralizes damaging natural substances called free radicals. It works in water, both inside and outside of cells. Vitamin C complements another antioxidant vitamin, vitamin E , which works in lipid (fatty) parts of the body.

Vitamin C is the single most popular vitamin supplement in the United States and perhaps the most controversial, as well. In the 1960s, two-time Nobel Prize winner Dr. Linus Pauling claimed that vitamin C could effectively treat both cancer and the common cold. Subsequent research has mostly discounted these claims, but hasn't dampened enthusiasm for this essential nutrient. The vitamin C movement has led to hundreds of clinical studies testing the vitamin on dozens of illnesses; at present, however, no dramatic benefits have been discerned.


Vitamin C is an essential nutrient that must be obtained from food or supplements; the body cannot manufacture it. The official US and Canadian recommendations for daily intake are as follows:

  • Infants
  • 0-6 months: 40 mg
  • 7-12 months: 50 mg
  • Children
  • 1-3 years: 15 mg
  • 4-8 years: 25 mg
  • 9-13 years: 45 mg
  • Males
  • 14-18 years: 75 mg
  • 19 years and older: 90 mg
  • Females
  • 14-18 years: 65 mg
  • 19 years and older: 75 mg
  • Pregnant Women
  • 18 years old or younger: 80 mg
  • 19 years and older: 85 mg
  • Nursing Women
  • 18 years old or younger: 115 mg
  • 19 years and older: 120 mg

Note: Smoking cigarettes significantly reduces levels of vitamin C in the body. 1 The recommended daily intake for smokers is 35 mg higher across all age groups.

Scurvy, the classic vitamin C deficiency disease, is now a rarity in the developed world, although a more subtle deficiency of vitamin C is fairly common. 2 3 4 5 According to one study, 40% of Americans do not get enough vitamin C. 6 In fact, vitamin C deficiency sufficient to cause bleeding problems during surgery turns out to be more common than previously thought. 7

Aspirin and other anti-inflammatory drugs might lower body levels of vitamin C, 8 9 as might oral contraceptives . 10 11 12 13 Supplementation may be helpful if you are taking any of these medications.

Most of us think of orange juice as the quintessential source of vitamin C, but many vegetables are actually even richer sources. Red chili peppers, sweet peppers, kale, parsley, collard, and turnip greens are full of vitamin C, as are broccoli, Brussel sprouts, watercress, cauliflower, cabbage, and strawberries. (Oranges and other citrus fruits are good sources, too.)

One great advantage of getting vitamin C from foods rather than from supplements is that you will get many other potentially healthful nutrients at the same time, such as bioflavonoids and carotenes. However, vitamin C in food is partially destroyed by cooking and exposure to air, so for maximum nutritional benefit you might want to try freshly made salads rather than dishes that require a lot of cooking.

Vitamin C supplements are available in two forms: ascorbic acid and ascorbate. The latter is less intensely sour.

Therapeutic Dosages

Ever since Linus Pauling, proponents have recommended taking vitamin C in enormous doses, as high as 20,000 mg to 30,000 mg daily. However, some evidence suggests that there might not be any reason to take more than 200 mg of vitamin C daily (10 to 100 times less than the amount recommended by vitamin C proponents). 14 The reason is that if you consume more than 200 mg daily (researchers have tested up to 2,500 mg) your kidneys begin to excrete the excess at a steadily increasing rate, matching the increased dose. Your digestive tract also stops absorbing it well. The net effect is that no matter how much you take, your blood levels of vitamin C don't increase very much.

However, there are some flaws in this research. It is possible that vitamin C levels might rise in other tissues even if they remain constant in the blood. Furthermore, this study did not evaluate the possible effects of taking vitamin C several times daily rather than once daily.

Many nutritional experts recommend a total of 500 mg of vitamin C daily. This dose is almost undoubtedly safe. Others recommend that you take as much vitamin C as you can, up to 30,000 mg daily, cutting back only when you start to develop stomach cramps and diarrhea. This recommendation seems based more on a semi-religious enthusiasm for the vitamin C than on any evidence that such huge doses of the vitamin are good for you.

Intravenous vitamin C can easily raise vitamin C levels to a level 140 times higher than the maximum achievable with oral vitamin C. 15 However, there is no meaningful evidence that intravenous vitamin C provides any medical benefits.

What Is the Scientific Evidence for Vitamin C?


As the most famous of all natural treatments for the common cold , vitamin C has been subjected to irresponsible hype from both proponents and opponents. Enthusiasts claim that if you take vitamin C daily, you will never get sick, while critics of the treatment insist that vitamin C has no benefit at all.

However, a cool-headed evaluation of the research indicates something in between. Numerous studies have found that vitamin C supplements taken at a dose of 1,000 mg daily or more throughout the cold season canmodestly reduce symptoms of colds and help you get over a cold faster, but they do notgenerally help prevent colds. 16

Reducing Cold Symptoms

Most studies on vitamin C have evaluated the potential benefits to be gained by taking vitamin C throughout the cold season. A review of 29 placebo-controlled trials involving over 11,000 people found that the use of vitamin C in this way can reduce symptoms and decrease the duration of colds. 17 Other studies have found similar results. 18 Many people use vitamin C for colds in a different way: they only begin taking it when cold symptoms start. Vitamin C is probably not effective when used in this way. 19 One double-blind trial enrolled 400 individuals with new-onset cold symptoms, and divided them into four different daily vitamin C dosage groups: 30 mg daily (a dose lower than the minimum daily requirement, and used by the researchers as a placebo), 1,000 mg, 3,000 mg, or 3,000 mg with bioflavonoids. 20 Participants were instructed to take the vitamin at the onset of symptoms and for the following 2 days. The results showed no difference in the duration or severity of cold symptoms among the groups. High-dose vitamin C taken at the onset of a cold, in other words, didn't help. A review of 7 randomized and non-randomized trials also found that taking vitamin C at the start of a cold did not offer any benefits. 21 The bottom line: If you want to use vitamin C to take the edge off your colds, take the supplement throughout the winter.

There are numerous other natural treatments for the common cold as well, some of which may be more helpful than vitamin C. For more information, see the full Colds and Flus article.

Preventing Colds

Although two relatively recent studies suggest that regular use of vitamin C throughout the cold season can help prevent colds, 22 they suffer from a variety of flaws, and most other studies have found little to no benefit along these lines. 23 However, people who are truly vitamin C-deficient, such as elderly people in nursing homes, may show increased resistance to infection if they take vitamin C (or other nutrients). 24 In addition, vitamin C might be helpful for preventing the respiratory infections that can follow heavy endurance exercise. Marathon running and similar forms of exertion can temporarily weaken the immune system, leading to infections. Vitamin C may be helpful. According to a double-blind, placebo-controlled study involving 92 runners, taking 600 mg of vitamin C for 21 days prior to a race, made a significant difference in the incidence of sickness afterwards. 25 Within 2 weeks of the race, 68% of the runners taking placebo developed cold symptoms versus only 33% of those taking the vitamin C supplement. As part of the same study, non-runners of similar age and gender to those running were also given vitamin C or placebo. Interestingly, the supplement had no apparent effect on the incidence of upper respiratory infections in this group. Vitamin C seemed to be effective in this capacity only for those who exercised intensively!

Two other studies found that vitamin C could reduce the number of colds experienced by groups of people involved in rigorous exercise in extremely cold environments. 26 One study involved 139 children attending a skiing camp in the Swiss Alps, while the other enrolled 56 military men engaged in a training exercise in northern Canada during the winter months. In both cases, the participants took either 1 g of vitamin C or placebo daily at the time their training program began. Cold symptoms were monitored for 1 to 2 weeks following training, and significant differences in favor of vitamin C were found.

However, one very large study of 674 US Marine recruits in basic training found no such benefit. 27 The results showed no difference in the number of colds between the treatment and placebo groups.

What's the explanation for this discrepancy? There are many possibilities. Perhaps basic training in the Marines is significantly different from the other forms of exercise studied. Another point to consider is that the Marines didn't start taking vitamin C right at the beginning of training, but waited 3 weeks. The study also lasted a bit longer than the positive studies mentioned above, continuing for 2 months; maybe vitamin C is more effective at preventing colds in the short term. Of course, another possibility is that it doesn't really work. More research is needed to know for sure.

Preeclampsia Prevention

Preeclampsia is a dangerous complication of pregnancy that involves high blood pressure, swelling of the whole body, and improper kidney function. A double-blind, placebo-controlled study of 283 women at increased risk for preeclampsia found that supplementation with vitamin C (1,000 mg daily) and vitamin E (400 IU daily) significantly reduced the chances of developing this disease. 28 While this research is promising, larger studies are necessary to confirm whether vitamins C and E will actually work. The authors of this study point out that similarly sized studies found benefits with other treatments, such as aspirin, that later proved to be ineffective when large-scale studies were performed. Furthermore, keep in mind that we don't know whether such high dosages of these vitamins are absolutely safe for pregnant women.

Cancer Treatment

Cancer treatment is one of the more controversial proposed uses of vitamin C. An early study tested vitamin C in 1,100 terminally ill cancer patients. One hundred patients received 10,000 mg daily of vitamin C, while 1,000 other patients (the control group) received no treatment. Those taking the vitamin survived more than four times longer on average (210 days) than those in the control group (50 days). 29 A large (1,826 subjects) follow-up study by the same researchers found a nearly doubled survival rate (343 days versus 180 days) in vitamin C-treated patients whose cancers were deemed "incurable," as compared to untreated controls. 30 However, these studies were poorly designed, and other generally better-constructed studies have found no benefit of vitamin C in cancer. 31 At the present time, vitamin C cannot be regarded as a proven treatment for cancer.

Reflex Sympathetic Dystrophy

Reflex sympathetic dystrophy (RSD) is a set of symptoms that can develop in the legs, arms, feet, and hands after fractures and other injuries. Also called complex regional pain syndrome (CRPS), symptoms include changes in skin temperature and color over the affected area, accompanied by burning pain, sensitivity to touch, sweating, and limitation of range of motion. The cause of RSD is unknown, and the condition is very difficult to treat.

Two studies performed by a single research group reported evidence that vitamin C can help prevent RSD after wrist fractures. 32 In one of these, a total of 123 adults with wrist fractures were enrolled and followed for one year. 33 All were given 500 mg of vitamin C or placebo daily for 50 days. The results showed significantly fewer cases of RSD in the treated group.

A subsequent study conducted by the same research group compared placebo against three dosages of vitamin C in 416 people suffering from wrist fracture. 34 Again, treatment continued for 50 days. The results indicated that approximately 10% of those given placebo developed RSD, while less than 2% of those given either 500 mg or 1,500 mg of vitamin C daily did so. According to the statistical analysis used by the authors, this relative benefit was statistically significant. The 200 mg dose of vitamin C did appear to offer some protection too, but not as much.

Easy Bruising

A 2-month, double-blind study of 94 elderly people with marginal vitamin C deficiency found that vitamin C supplements decreased their tendency to bruise . 35

Hypertension (High Blood Pressure)

According to a 30-day, double-blind study of 39 individuals taking medications for hypertension , treatment with 500 mg of vitamin C daily can reduce blood pressure by about 10%. 36 Smaller benefits were seen in studies of individuals with normal blood pressure or borderline hypertension. 37 However, other studies have failed to find any significant blood pressure-lowering effect. 38 This mixed evidence suggests, on balance, that if vitamin C does have any blood pressure-lowering effect, it is at most quite small.

Maintaining the Effectiveness of Nitrate Drugs

Nitroglycerin and related nitrate medications are used for the treatment of angina. However, the effectiveness of these medications tends to diminish over time. According to a double-blind study of 48 individuals, use of vitamin C at a dose of 2,000 mg 3 times daily helped maintain the effectiveness of nitroglycerin. 39 These findings are supported by other studies as well. 40 41

Note: Angina is too serious a disease for self-treatment. If you have angina, do not take vitamin C (or any other supplement) except on a physician’s advice.


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