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Pro-Vitamin Supplement May Increase Cancer Risk in Smokers and Drinkers

HANOVER, NH - Smokers and drinkers who take beta-carotene supplements to help prevent cancer may actually increase their risk, new research finds. The study, led by Dartmouth Medical School (DMS), provides a cautionary perspective regarding the alleged cancer-fighting attributes of beta-carotene and other antioxidants. It is published in the May 21 issue of the Journal of the National Cancer Institute.

Dr. John A. Baron, professor of medicine at DMS, and his colleagues found that for participants who smoked cigarettes and drank more than one alcoholic drink per day, the vitamin A precursor beta-carotene doubled the risk of recurring adenomas. Adenomas are benign tumors that could lead to colorectal cancer. In non-smokers or non-drinkers, beta-carotene supplementation was associated with a 44 percent decrease in the risk of colorectal adenoma recurrence, compared to those subjects who received a placebo.

"The key point of the study was the supplements had different effects, depending on the smoking and drinking habits of the subjects," Baron said. "These findings illustrate the complexity that we face in designing safe and effective chemopreventive strategies for any cancer. A careful mix of animal studies, epidemiology and clinical trials is needed," he said, to continue to determine successful methods of preventing cancer.

The examination of smoking and drinking on adenomas builds on previous large clinical trials focused on lung cancer. Two of these, which included mainly cigarette smokers, found that beta-carotene supplementation was associated with an increased risk of lung cancer, particularly among those who also drank alcohol. A third randomized trial, which enrolled mostly nonsmokers, found no association between beta-carotene supplementation and risk of lung cancer, suggesting that cigarette smoking and alcohol intake were somehow associated with the adverse effects of beta-carotene.

This new randomized study examined data on 864 people who had participated in the Antioxidant Polyp Prevention Study. The participants, who were polyp-free after having had previous polyps removed, were randomly assigned to receive a placebo, beta-carotene, vitamin C plus vitamin E, or beta-carotene plus vitamins C and E. Participants completed a questionnaire about their smoking habits and alcohol intake.

The authors point out that the alcohol and smoking habits were reported by the subjects, so there is a potential for measurement error and association with other unknown lifestyle factors. Nonetheless, Baron and his co-authors conclude that, "Supplementation [with beta-carotene] was beneficial among subjects who did not drink or smoke but, if anything, increased risk among those who drank and/or smoked."

The study was conducted at four centers across the US, including the Norris Cotton Cancer Center at Dartmouth-Hitchcock Medical Center. In addition to Baron, DMS researchers were Dr. Bernard Cole, Dr. Maria Grau, Dr. Robert Greenberg and Leila Mott.