beta-carotene supplementation for patients with low baseline levels and decreased risks of total and prostate carcinoma

BAGKGROUND, The Physicians' Health Study was a randomized, double-blind, pl acebo-controlled trial using a 2 x 2 factorial design including supplementa tion with beta-carotene (50 mg every other day) in the primary prevention o f cancer among 22,071 U.S. male physicians ages 40-84 years at randomizatio n. Before randomization, the authors collected baseline blood specimens to determine whether any benefit was greater among or confined to those with l ow baseline levels of beta-carotene. METHODS, Baseline blood samples were collected from 14,916 participants. Th ese samples were assayed, according to a nested case-control design, from 1 439 men subsequently diagnosed with cancer over 12 years of follow-up (631 with prostate carcinoma) and 2204 controls matched by age and smoking habit s. RESULTS, Men in the lowest quartile for plasma beta-carotene at baseline ha d a marginally significant (P = 0.07) increased risk of cancer compared wit h those in the highest quartile (relative risk [RR] = 1.30, 95% confidence interval [CI], 0.98-1.74). Men in the lowest quartile assigned at random to beta-carotene supplementation had a possible but nonsignificant decrease i n overall cancer risk (RR = 0.83, 95% CI, 0.63-1.09] compared with those as signed to placebo. This was primarily due to a significant reduction in the risk of prostate carcinoma (RR = 0.68, 95% CI, 0.46-0.99) in this group. A fter the first 2 years of follow-up were excluded, the results were virtual ly unchanged. CONCLUSIONS. These prespecified subgroup analyses appeared to support the i dea that beta-carotene supplementation may reduce risk of prostate carcinom a among those with low baseline levels. Further follow-up of this populatio n will help determine whether these findings are valid. [See editorial on p ages 1629-31, this issue.] (C) 1999 American Cancer Society.