BOSTON, MASSACHUSETTS. Numerous epidemiological studies have concluded that high intakes of fruits and vegetables are associated with lower risks of cancer. It was originally thought that beta-carotene was the protective component, but six large- scale clinical trials have failed to confirm any cancer-protective effects. Two of the trials involving heavy smokers showed a significant 18 per cent increase in lung cancer among the smokers who took beta-carotene. One very large trial involving 22,071 American physicians showed no benefits and no harm from 12 years of supplementation with 50 mg of synthetic beta-carotene every second day.
Researchers at the Harvard Medical School have just released the results of a major study aimed at evaluating the effects of beta- carotene supplementation among women. The study involved almost 40,000 healthy female health professionals (aged 45 years or older). The women were randomized into two groups with one group receiving 50 mg of synthetic beta-carotene on alternate days and the other group receiving a placebo. The 2.1-year supplementation phase of the study was followed by a two-year observation period. At the end of the four years 747 cases of cancer and 218 cases of cardiovascular incidents (heart attack, stroke, and death) had occurred among the women. There were no significant differences in the incidence of cancer, cardiovascular events or death from all causes in the two groups. This also held true when just the smokers among the women were considered.
The researchers conclude that beta-carotene supplementation is neither harmful nor beneficial to people at average risk for cancer except in the case of prostate cancer. The Physicians' Health Study found that men who supplemented with 50 mg of beta- carotene every second day for 12 years had a significantly lower incidence of prostate cancer.
Lee, I. Min, et al. Beta-carotene supplementation and incidence of cancer and cardiovascular disease: the Women's Health Study. Journal of the National Cancer Institute, Vol. 91, December 15, 1999, pp. 2102-06