Some recent studies have suggested that several dietary antioxidants may reduce the risks of developing prostate cancer. The Physicians' Health Studyis a well-known, randomized, double blind placebo-controlled trial of ß-carotene (50 mg every other day) and aspirin, designed to evaluate a number of health outcomes. A previous analysis of data failed to demonstrate any protective effect of ß-carotene supplementation on total or prostate cancer incidence in the cohort. The current study looked at the potential benefits of ß-carotene supplements in the subgroup of participants who had lower than average plasma baseline levels of ß-carotene.
Baseline plasma ß-carotene levels were measured from nearly 15,000 male physicians prior to randomization. The team focused on the effects of ß-carotene on cancer risk in 1,439 men who subsequently developed cancer during 12 years of follow-up and 2,204 matched controls from the cohort.
There was a modest and nearly significant increase in risk of developing cancer for men in the lowest versus the highest quartile of baseline plasma ß-carotene level.
Men in the lowest quartile of initial plasma ß-carotene who subsequently randomized to receive ß-carotene supplementation experienced a significant reduction in risk of prostate carcinoma.
Men in the highest baseline quartile, ß-carotene supplements were associated with non-significant 33% increase in risk of prostate cancer.
ß-carotene supplements appeared to reduce risk of developing prostate carcinoma among men with low baseline plasma ß-carotene levels. In contrast, men with higher concentrations of plasma ß-carotene may not benefit or may even show an increased risk of prostate carcinoma with ß-carotene supplementation. Additional investigation is needed to assess efficacy and optimal dosing of ß-carotene supplements for men with low baseline plasma ß-carotene level.