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.