A new study of French women has found that high beta-carotene intake--through a combination of diet or supplementation--is associated with a higher risk of tobacco-related cancers in smokers, but the risk of these cancers decreases with increasing beta-carotene intake in nonsmokers. The study appears in the September 21 issue of the Journal of the National Cancer Institute.
Some observational studies have found that beta-carotene consumption is associated with a decreased risk of cancer. However, some intervention studies have suggested that high doses of the antioxidant, given through supplementation, may be associated with an increased risk of lung cancer and digestive cancers in smokers.
To investigate the relationships of beta-carotene intake from both diet and supplementation with the risk of tobacco-related cancers--which include colorectal, thyroid, ovarian, cervical, and lung cancers in addition to less common cancers--Marie-Christine Boutron-Ruault, M.D., Ph.D., of INSERM in Villejuif, France, and colleagues used information from questionnaires given in 1994 to nearly 60,000 women from the French Etude Epidémiologique de Femmes de la Mutuelle Générale de l'Education Nationale (E3N) prospective study. The researchers assessed diet, supplement use, and smoking status in these women and followed them for a median of 7.4 years.
During the follow-up period, 700 women developed a type of cancer known to be related to smoking. Among women who never smoked, beta-carotene intake was inversely associated with the risk of developing a tobacco-related cancer, with a dose-dependent relationship across the considered beta-carotene categories (tertiles of dietary beta-carotene, and supplement use as the fourth category). However, among women who had ever smoked, the results were reversed: cancer risk was highest among women in the high beta-carotene intake group.
In the population studied, the authors calculated that the absolute rates of tobacco-related cancers over 10 years for nonsmokers with low and high beta-carotene intakes were 181.8 and 81.7 cases per 10,000 women, respectively. Among smokers, these rates were 174.0 cases per 10,000 women for those who had low beta-carotene intake and 368.3 cases per 10,000 women for those who had high intake.
"Although beta-carotene may act as a cocarcinogen, there is no evidence that smokers should avoid consuming beta-carotene-rich foods such as fruit and vegetables, in which other components, such as vitamins C and E, may counteract a potentially deleterious interaction of beta-carotene with smoking," the authors write.
In an editorial, Susan T. Mayne, Ph.D., of the Yale University School of Medicine and Yale Cancer Center in New Haven, Conn., and Scott M. Lippman, M.D., of the University of Texas M. D. Anderson Cancer Center in Houston, write that "evidence suggesting that tobacco exposure modifies the chemopreventive efficacy of nutrients/nutrient derivatives continues to mount." However, this new research "should not alter our current policy recommendations with regard to nutrients and cancer risk. Rather, this new research emphasizes the need to examine current, former, and never smokers separately in studies of nutrient supplements and other preventive agent classes in a wide spectrum of cancer prevention settings," they write.
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