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VITAMIN C and CANCER

Abstract:  Results from 29 study comparison sets found show that Vitamin C in average amounts of about 400 mg. per day may reduce risk of most types of cancer by about by 23% after 10 -15 or more years of its use.   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 200-250 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 appears to reduce risk of cancer similarly.  See the discussion on Vitamin C and Heart Disease for more about Vitamin C.

Results for 29 comparisons in 23 studies of Vitamin C in reducing risks of cancer in the table following provide a average risk benefit of about 0.77 or risk reduction of 23%.  24 of the comparisons showed benefits for Vitamin C;  5 found no benefit and possible reasons for those that found no benefits are suggested.  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. The nurses averaged much younger than did participants of the other studies, and many were pre-menopausal. Also the nurses appear to have used appreciably more other antioxidant supplements in their diets than did other groups. This average result is for typical differences of about 400 mg per day of Vitamin C from diet plus supplements. Larger amounts of the vitamin should produce somewhat large benefits.

The table following lists the number of study comparisons found for each type of cancer and average for all comparisons.  Benefits are  noted for each type of cancer, the risks probably all are statistically consistent with the average risk factor of 0.77 for the 23 comparisons.  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.  Similar risks were indicated for the various types of cancer, but results did not have the accuracy to identify specific differences.  Most benefits for Vitamin C were measured from diets of foods.

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 about 0.983 per year of exposure for a difference of 400 mg per day of Vitamin C from diet plus supplements up to a maximum duration of 20 years.  This produces a risk reduction of about 25% after 20 years.   The risks of cancer from Vitamin C are the same as those for the vitamin in reducing risks of cardiovascular disease.  Thus the same formula will apply for both risks.  This formula follow the table of results. Some values from the formula are in the following table:

Risk Ratios of Cancer from Amount and Duration of Vitamin C

The effect of Vitamin C is identified only as one of 4 antioxidants that have a limit imposed on their multiple amounts. See the Global antioxidant model for more on this. Thus for best assured benefits individuals should consume some amounts of each as each antioxidant probably provides a partly different combination of benefits.  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.

Men may develop a somewhat higher benefit for cancer risk from vitamin C than do women  This is noted in Studies A1, A2, and R1. It also is possible that pre-menopausal women may obtain less benefit from antioxidants because of the protective effect of estrogen.   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, antioxidant vitamins been found to reduce risk of other problems including cataracts, cognitive impairment, arthritis, asthma and macular degeneration.

See other papers of antioxidants and CV disease for Vitamin E;  Vitamin A;  Vitamin C; and Selenium , papers of antioxidants and cancer for Vitamin E;  Vitamin A; and Selenium, and Antioxidants, Death from All Causes and Antioxidants, a Global Analysis.

A formula for estimating risk of cancer from use of Vitamin C"

amt is amount of Vitamin C in mg

yrs is duration of use of Vitamin C

Risk ratio =  exp( -0.00094 * yrs * amt^^{0.5 )}