ANTIOXIDANTS and CANCER
A GLOBAL ANALYSIS
Abstract: The combined results from more than 90 research study comparisons confirm that dietary antioxidants can substantially reduce the risk of most types of cancer. As for cardiovascular diseases, Life Ahead combines the benefits of antioxidants Vitamin E, Beta carotene, Vitamin C and Selenium with an imposed limit on their combined benefits. Antioxidants reduce risk of cancer in accord with their duration of exposure. Risk ratios obtained from individual nutrients vary from 0.958 to 0.972 per year of exposure, with a minimum risk ratio taken as 0.95 per year. A minimum risk ratio of 0.50 for any amount or duration of these factors now used in Life Ahead may be identify benefits conservatively. But antioxidants may not benefit the cancer risk of pre-menopause women.
Background: Antioxidants included in both foods and in dietary supplements can reduce substantially the risk of cancer. And this key health benefit probably is obtained for all or nearly all types of cancer. The benefits of the four key supplements included in the antioxidant model for cardiovascular diseases are similarly defined for cancer from all key research published and found in the links herein for Vitamin E, Betacarotene and Vitamin C and Selenium. Interestingly, although antioxidants have most often been referred to as associated with cardiovascular diseases (CVD), more studies were located relating antioxidants to cancer than were found for heart diseases. Further their benefit to reducing risk of cancer appears quite similar to their benefits in reducing risk of CV diseases.
The Research: The research results on Vitamin E in reducing risk of cancer are impressive, suggesting a reduction in a risk of about one third for men and post-menopausal women. This is the average benefit from a total of 25 population study comparisons for amounts of about 200 IU per day. The averaged risk ratio benefit for 21 study comparisons relating about 14,000 IU of beta carotene to cancer was 0.75. The averaged benefit found in 21 comparisons relating 400 mg of Vitamin C supplements to cancer was 0.71. And most interesting, the average benefit found in a total of 31 different researched comparisons for Selenium was a low risk ratio of 0.61. See the above links for the actual data and discussions of the more than 90 different research study comparisons that in aggregate confirm the benefits of antioxidants in reducing risk of cancer with highest probability. For example, the risk ratio and error margin for Vitamin E alone from the 25 included research comparisons is 0.67 (5%-95% limits about 0.59-0.75). And this is for a typical 200 IU of the vitamin vs. the 400 IU often taken.
Much on how antioxidants reduce risk of cancer parallels the process by which they reduce risk of CVD disease. Thus this Global Analysis will not review the process of risk reduction in the detail that is included for Antioxidants and CVD disease. Antioxidants are components of diet that are involved in DNA and cell maintenance and repair. Vitamin E and other antioxidants have been found to inhibit human prostate cancer cells. And there is considerable laboratory evidence from chemical, cell culture and animal studies that antioxidant vitamins and related micronutrients are able to slow the carcinogenic process. Life Ahead assumes that pro and antioxidants respectively enhance or slow the growth of cancer cells over time. Thus their biochemical effects must be duration related for cancer as appears true for cardiovascular diseases and cigarettes. Antioxidants appear to benefit all types of cancer, and a likely hypothesis now is that all or nearly all types will be benefited near similarly.
A summary of the average risk ratios for each antioxidant obtained from the more detailed analysis provided in the Life Ahead library follows. More detail and actual research information on each factor is available in the library at the indicated links. Risk ratios are summarized vs. a typical amount of factor used for both an estimated 10 years duration and per year of use:
For Nutrient Vitamin E Beta carotene Vitamin C Selenium
Avg Amount in research 200IU 14,000IU 400mg 100mcg
Avg Research Risk Ratio 0.67 0.75 0.71 0.61
Formula Value 0.67 0.75 0.71 0.65
Risk Ratio per year of use 0.961 0.972 0.966 0.958
No Research Population
Study Risk Ratios used 25 21 14 31
The Global Formula: The formula for relating antioxidants to risk of cancer is similar in concept to the formula for antioxidants and CVD diseases. Risk is taken as a ratio to that for average nutrient dietary inclusion in the foods of a typical US population. Coefficients differ somewhat based on the available research as follows:
Cancer risk = Exp( - 0.002 * (Vitamin E, IU - 8) - 0.000020 * (Beta carotene, IU - 3500)
- 0.00085 * (Vitamin C, mg - 250) - 0.0043 * (Selenium, mcg - 90)
The results for each of the antioxidants showed that most types of cancer researched benefited similarly from overall antioxidants. An exception was that risk of women's cancer for breast and genital areas did not appear to benefit from antioxidants until after menopause.
The benefits for Vitamin E, Beta carotene, and Vitamin C are taken by the formula as the average values found in the accompanying research. Benefits for Selenium which are potentially quite large are modified slightly for conservatism. The most pertinent values used in Life Ahead for these nutrients in both foods and dietary supplements are the risk ratios per year of use - as for CVD diseases. The benefits of antioxidants in foods are similarly compared with those of an average diet of a US person. Maximum values credited for supplements in benefiting cancer are 400 IU for Vitamin E, 15,000 IU of Beta-carotene, 400 mg of Vitamin C, and 100 mg of Selenium as these values are those now confirmed by actual research results.
A maximum benefit on risk of cancer now taken in Life Ahead for any amount of or kind or combination of antioxidants is a reduction in risk of 5% per year or use, or an annual compounding risk of 0.95. Duration of use is taken for only a maximum of 20 years of use, and then only to a minimum overall risk factor of 0.50. This is the same maximum benefit credited for heart disease. These limits may be conservative in view of much lower risks found for Vitamin E and Selenium combinations. But the use of some limit appears appropriate to recognize that there must a defined biochemical limit to what antioxidants can accomplish in slowing cancer, and actual available research does not convincingly confirm overall risk benefits much beyond these arbitrary limits imposed.
A combination of any two of the above antioxidants at the above maximum accepted amounts should eventually produce these maximum credited benefits. But it is suggested that to assure adequate benefit all four antioxidants be taken, in at least 1/2 and preferably for the maximum amounts suggested for each individually. The different antioxidant nutrients may act via supplementary mechanisms. As noted for individual supplements, Life Ahead does not credit any cancer benefit to antioxidant supplements for pre-menopausal women. Also, no credit for beta-carotene is given to smokers. But overall benefits to heart disease alone for dietary supplements should be more than sufficient to convince any health-interested man or woman that they should take them regularly.
As for their effect on CV diseases, practical diets rarely will include sufficient antioxidants to reduce risk of cancer by more than about 15%. Thus use of these dietary supplements becomes an essential need to achieve adequate reduction of cancer risk by diet.
See the Global Antioxidant Model for CV diseases for the way in which Life Ahead computes results for antioxidants, for estimates on the value of using supplements, for Well-Days potential from use of antioxidants and for possible ways to improve the present Model.