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VITAMIN C and CANCER

Abstract:  Results from 12 key studies found show that Vitamin C in average amounts of about 400 mg. per day reduces risk of most types of cancer by about by 25% after 7-10 or more years of its use.  But pre-menopausal women probably will not obtain reduced cancer risk from added use of Vitamin C.  Benefits appear indicated up to about 750 mg per day of the Vitamin in the total of both foods plus supplements.  Because a usual amount in food will be only about 200 mg per day, and Vitamin C also reduces risk of heart disease, use of a daily supplement of 500 mg of Vitamin C would appear prudent for most health-interested men and women.

Vitamin C has been widely publicized as an agent to reduce risk of heart disease.  But research now shows that as an antioxidant it also can reduce risk of cancer.  See the discussion on Vitamin C and Heart Disease for more about Vitamin C.

Results for Vitamin C in reducing risks of cancer in the table following provide a more consistent picture of benefit than do the results for Vitamin A.  The Nurse's study found no benefit in studies #1 and 6 for its younger than usual group of women, similar to their results found for other antioxidant vitamins and selenium.  But the average of all other results and which usually were for older women and men develop a average risk ratio of 0.71. These other results are statistically consistent or near so with this value. This result is for a typical differences of about 400 mg per day of Vitamin C from diet plus supplements.  No useful randomized clinical study results were found for Vitamin C but it is unlikely that such a study done for less than 10-15 years would be able to measure usefully a correct long range effect of this or any other antioxidant.

Insufficient research was found to identify a differing effect of Vitamin C on different types of cancer. Thus as for heart disease and as for the much more extensive research on antioxidant Vitamin E on cancer a single risk now is applied to all types of cancer.  Risk values in Life Ahead are taken vs. an average of 200 mg per day of Vitamin C for the average base US population used as a reference.

As for its effect on heart disease, Vitamin C probably acts to reduce the rate of cancer development, and this will reduce risk at a modest value for each year of use.  Life Ahead now uses a risk value for cancer of 0.970 per year of exposure for a difference of 400 mg per day of Vitamin C from diet plus supplements.  This produces a risk reduction of about 25% after ten years of vitamin use.  As for other antioxidants, no benefits for Vitamin C in reducing cancer risk is included for pre-menopausal women. Women may have to reach nearly age 60 before a useful effect of Vitamin C in reducing cancer risk develops.

The effect of Vitamin C is identified only as one of 4 antioxidants that have a limit imposed on their multiple amounts. See the antioxidant model for more on this.  This behavior is assumed for effects of the antioxidants on both cardiovascular diseases and cancer.  Thus if adequate antioxidants are provided from other vitamins, minerals, or sources, no added benefit from Vitamin C may be achieved.

Both men and women appear to obtain some reduction in heart disease from use of adequate amounts of Vitamin C.  Most diets may average only 200 to 250 mg/day of the vitamin.  Because benefits appear useful up to amounts of about 750 mg/day, the research to date suggests that health-interested persons should consider taking a 500 mg/day supplement of Vitamin C each day. Beyond its potential value in reducing risk of the major diseases, Vitamin E has been found to reduce risk of other problems including cataracts, cognitive impairment, arthritis, asthma and macular degeneration.