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Study Finds Beta-Carotene Supplements May Actually Be Dangerous
Women who have had breast cancer may have a lower or higher risk of recurrence if they take antioxidant supplements, depending on the supplement they take.
A newly published study of 2,264 women who had breast cancer in the journal Cancer found that women who took vitamins C and E were 27% less likely to die of breast cancer and 24% less likely to die of any cause during the study period. On the other hand, women who took carotenoid supplements (vitamin A, beta-carotene, gamma-carotene, and lutein) were 107% more likely to die of breast cancer and 75% more likely to die of any cause during the same period.
Why should vitamin A be harmful while vitamins C and E seem to be helpful?
First, it is important to understand that the data on antioxidants and breast cancer are equivocal. Just a month before the Cancer study came out, a study of 4,824 women in Canada found that among women who had never had cancer:
- Taking a multivitamin regularly reduced the risk of ever having breast cancer by 26%,
- Taking beta-carotene supplements regularly reduced the risk of ever having breast cancer by 42%,
- Taking vitamin C regularly reduced the risk of ever having breast cancer by 21%,
- Taking vitamin E regularly reduced the risk of ever having breast cancer by 25%, and
- Taking zinc regularly reduced the risk of ever having breast cancer by 53%, if
women had taken these supplements for 10 years or more. Eating healthy foods did not lower (or raise) the risk of getting breast cancer for the first time, and taking supplements for less than 10 years did not lower (or raise) the risk of getting breast cancer for the first time. It is possible, of course, that women who take nutritional supplements for much of their lives also have other healthy habits that reduce the risk of breast cancer.
So it seems that something about the usefulness of antioxidants changes when women have cancer. What could be going on?
The answer seems to be that vitamin A, beta-carotene, and lycopene protect DNA from changes. In women who have never had breast cancer, they keep DNA damage from causing the formation of cancerous cells. In women who have already had breast cancer, they probably keep DNA from being repaired. The effect is greatest in women who have breast cancer tumors that are activated by both estrogen and progesterone.
The bottom line of the studies of women's breast cancer and nutrition seems to be that long-term use of supplements may be helpful to women's health but they are not a guarantee against breast cancer. Once breast cancer has occurred, supplements not only don't help, they may even hurt. But what about the same antioxidant supplements and cancer in men?