Vitamin C, also known as ascorbic acid, is an essential water-soluble vitamin that plays vital roles in collagen production, protein metabolism, immune function and iron absorption. The daily recommended dietary allowance of vitamin C is 75 mg for adult women and 90 mg for adult men, but there is some evidence to suggest that doses as high as 500 mg per day may offer additional health benefits. Supplement manufacturers offer vitamin C in a buffered form for those who experience gastrointestinal discomfort when taking non-buffered vitamin C supplements.
Cancer
Dietary vitamin C intake of at least 80 to 110 mg per day is associated with reduced risk of lung, breast, colon, stomach, oral cavity, laryngeal and esophageal cancers, according to the National Institutes of Health Office of Dietary Supplements. However, there doesn't seem to be a corresponding reduction in cancer risk associated with high-dose vitamin C supplementation. In a nine-year study conducted by the Brigham and Women's Hospital and Harvard Medical School that looked at the effects of supplemental antioxidants on 8,171 women, researchers found no significant reduction in cancer incidence or cancer mortality in women assigned to take 500 mg of vitamin C per day when compared to women in the placebo group.
Colds
While vitamin C is often taken to prevent or treat colds, there is very little evidence to back up this practice. The Linus Pauling Institute at Oregon State University reports that a 2007 meta-analysis of 30 previous placebo-controlled studies looking at the effect of supplemental vitamin C on cold prevention and treatment revealed that vitamin C in doses of at least 200 mg per day did not prevent colds. Supplemental doses of 250 mg to 1 g per day did reduce the durations of colds by 8 percent in adults and 14 percent in children; these supplemental doses offer a 50 percent reduction of cold incidence in adult marathoners, skiers and soldiers in extreme or arctic training situations.
Coronary Heart Disease
While diets rich in vitamin C are associated with a lower risk of cardiovascular disease, evidence that high-dose vitamin C supplementation may lower cardiovascular risk is contradictory. An analysis of nine studies of 293,172 participants who did not have coronary heart disease at the beginning of the study revealed a 25 percent lower risk of developing the disease in participants who took at least 700 mg of supplemental vitamin C per day. Conversely, the same Brigham and Women's Hospital and Harvard Medical School study that found no reduction in cancer rates or mortality in women taking 500 mg of supplemental vitamin C per day also found no reduction in coronary heart disease rates in those women.
References
- National Institutes of Health Office of Dietary Supplements: Vitamin C
- The Linus Pauling Institute: The Bioavailability of Different Forms of Vitamin C
- Journal of the National Cancer Institute: Vitamins C and E and beta carotene supplementation and cancer risk: a randomized controlled trial
- Linus Pauling Institute: Vitamin C
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