Beta-Carotene's Benefits Thwarted by Cigarettes, Alcohol

LOS ANGELES--Alcohol intake and cigarette smoking seem to alter the beneficial effects of beta-carotene supplementation in terms of colorectal cancer risk, according to a study published in the May 21 issue of the Journal of the National Cancer Institute (95, 10:717-22, 2003) (jncicancerspectrum.oupjournals.org). Researchers from the University of Southern California in Los Angeles stated that although beta-carotene did not appear to increase general cancer risk in two large, randomized, lung cancer prevention trials, it was unknown whether smoking and/or alcohol would alter beta-carotene's effects on cancers other than lung cancer.

Researchers studied the effects of beta-carotene supplementation on recurrence of colorectal adenoma (benign tumors in the colon or rectum) among subjects in a multicenter, double blind, placebo-controlled trial of antioxidants for the prevention of colorectal cancer. Researchers recruited 864 subjects who had had a colon adenoma removed and were polyp-free at baseline. For four years, subjects were randomly assigned to take one of four regimens: 1) 25 mg/d of beta carotene plus 1,000 mg/d of vitamin C and 400 mg/d of vitamin E; 2) beta-carotene plus placebo; 3) placebo plus vitamins C and E; or 4) placebo. Researchers noted 707 of the original volunteers reported for the follow-up examinations at one year and at four years.

Among subjects who abstained from smoking and drinking, beta-carotene was associated with a significant decrease in the risk of one or more recurrent adenomas; however, supplementation with the nutrient modestly increased the risk of recurrence among smokers. In smokers who also drank more than one alcoholic beverage per day, beta-carotene doubled the risk of adenoma recurrence.