Vitamin's Effect on Cancer Varies by Smoker Status

NEW YORK (Reuters Health) - High intake of beta-carotene seems to decrease the risk of tobacco-related cancers among people who've never smoked, but to increase the risk among current or past smokers, new research suggests. Although the findings are based on a study of women, the researchers believe that similar results would be obtained in men.

"Based on the findings from our study and others, I would advise against beta-carotene supplements for current or past smokers," senior author Dr. Marie-Christine Boutron-Ruault, from INSERM in Villejuif, France, told Reuters Health. "For beta-carotene-rich foods, the message is less clear, since they often contain other vitamins that may counteract the interaction of beta-carotene with smoking."

The new study, which is reported in the Journal of the National Cancer Institute, involved an evaluation of beta-carotene intake for 59,910 women who were followed for about 7 years to assess cancer occurrence. During follow-up, 700 women developed tobacco-related cancers, such as lung cancer or head and neck cancer.

Among never smokers, consuming a diet containing moderate amounts of beta-carotene cut the risk of cancer by up to 28 percent. Taking beta-carotene supplements reduced the risk by 56 percent.

Just the opposite effect was seen in current or past smokers. In this group, consuming a diet containing moderate amounts of beta-carotene increased the risk of cancer by up to 43 percent. Taking beta-carotene supplements more than doubled the risk of cancer.

"We were surprised at the completely opposite effect high beta-carotene intake had on cancer risk depending on whether you had never smoked or ever smoked," Boutron-Ruault noted.

"We plan on doing a larger study with more cancer cases, a larger variety of doses of beta-carotene and tobacco, and both men and women" to verify and expand on the current findings, she added.

SOURCE: Journal of the National Cancer Institute, September 21, 2005.