Vitamin C
Background and Health Claims
Linus Pauling and Ewan Cameron completed research in the 1970s that popularized the idea of using vitamin C as a cancer treatment. Their published research concluded that 10 g of vitamin C taken daily improved quality of life and survival of terminal cancer patients compared with patients who did not take vitamin C. It was later discovered that the study groups were not comparable, placing the conclusions into question. The Mayo Clinic subsequently conducted three prospective, randomized, placebo-controlled trials using 10 g of vitamin C in the treatment group and found no benefit to patients with advanced cancer.
Vitamin C is being studied for cancer prevention. It may reduce the risk of gastric, pancreatic and laryngeal cancers.
Precautions
Taking megadoses of vitamin C may lead to kidney damage, diarrhea, iron overload and accelerated atherosclerosis (hardening of the arteries). It increases the risk of kidney stones in some people. If stopped abruptly, it may result in rebound scurvy (vitamin C deficiency). Doses between 2000 and 5000 mg per day may have anti-coagulant properties, making it difficult for people to stop bleeding.
One controversial study associated 500 mg of vitamin C supplementation with DNA damage to white blood cells. Another report indicated vitamin C may interfere with the absorption of vitamin B12 and vitamin E.
Dose
Receiving large amounts of vitamin C from natural food sources is probably not harmful. Patients should follow the recommended daily allowances*. Those guidelines were increased in 2000 to 75 mg for women and 90 mg for men. An additional 35 mg per day is recommended for smokers. The changes include a new maximum upper limit of 2000 mg per day. This limit includes intake from food and supplements.
The amount of vitamin C that may protect against some cancers is not currently known.
View maximum tolerable doses* for various vitamins.
*From the National Academy Press (NAP). Webpage will open in a new browser window. M. D. Anderson does not endorse external sites.