Beta-carotene supplements appear to promote the recurrence of potentially pre-cancerous colon polyps in people who smoke and drink regularly, researchers reported last week.
Their study is the latest to raise concerns about beta-carotene supplements in some people. Previous research found the pills might also increase the risk of lung cancer among those who smoke and drink. Beta-carotene supplements seem to work in an adverse way with regard to cancer when they're combined with smoking and/or alcohol. The reason, however, is unclear.
Beta-carotene is converted by the body into vitamin A. Researchers have thought beta-carotene acts as an antioxidant, mopping up cell-damaging substances called free radicals that may promote cancer.
And, in fact, the research team found that among patients who neither smoked nor drank, beta-carotene supplements were associated with a lower risk of polyp recurrence. But the study, along with others, suggests beta-carotene might actually fuel cancer in some situations, such as when it is taken in high supplemental doses by people who also smoke and drink.
His study involved 864 people who had colon polyps removed. Colon polyps are benign growths that can become cancerous. In an effort to determine whether antioxidants help prevent polyps from recurring, the researchers divided the participants into four groups. They received either beta-carotene supplements, vitamins C and E, beta-carotene plus vitamins C and E, or placebo pills.
At the end of 4 years, none of the supplements had an overall impact on polyp recurrence. But when the researchers divided people into groups according to whether they smoked or drank, they did find effects for beta-carotene. People who took 25-milligram beta-carotene supplements and also smoked and drank more than one alcoholic beverage a day were twice as likely to have a colon polyp recurrence as those who took placebo pills.
Smoking and drinking, individually, also appeared to promote recurrences among those taking beta-carotene, but not as much as when combined. On the other hand, beta-carotene supplements seemed to benefit those who did not smoke or drink, reducing their risk by 44%.
The researchers said the findings do not provide strong enough evidence to recommend that people should be taking supplements to ward off colon polyps or cancer.
And they pointed out that while beta-carotene supplements were linked to a greater risk of polyp recurrence in some study participants, that doesn't necessarily mean the pills actually promote colon cancer.
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