Beta-carotene supplementation for patients with low baseline levels and decreased risks of total and prostate cancer

Division of Preventive Medicine, Department of Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston, Massachusetts 02215, USA.
Cancer (Impact Factor: 4.89). 11/1999; 86(9):1783-1792. DOI: 10.1002/(SICI)1097-0142(19991101)86:93.0.CO;2-N


The Physicians' Health Study was a randomized, double-blind, placebo-controlled trial using a 2x2 factorial design including supplementation with beta-carotene (50 mg every other day) in the primary prevention of cancer among 22,071 U.S. male physicians ages 40-84 years at randomization. Before randomization, the authors collected baseline blood specimens to determine whether any benefit was greater among or confined to those with low baseline levels of beta-carotene.
Baseline blood samples were collected from 14,916 participants. These samples were assayed, according to a nested case-control design, from 1439 men subsequently diagnosed with cancer over 12 years of follow-up (631 with prostate carcinoma) and 2204 controls matched by age and smoking habits.
Men in the lowest quartile for plasma beta-carotene at baseline had a marginally significant (P = 0.07) increased risk of cancer compared with 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 in overall cancer risk (RR = 0.83, 95% CI, 0.63-1.09) compared with those assigned 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. After the first 2 years of follow-up were excluded, the results were virtually unchanged.
These prespecified subgroup analyses appeared to support the idea that beta-carotene supplementation may reduce risk of prostate carcinoma among those with low baseline levels. Further follow-up of this population will help determine whether these findings are valid.

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