BACKGROUND: The use of beta-carotene supplements has yielded mixed results in the prevention of lung cancer. Although supplements may reduce the risk of lung cancer among people who do not smoke tobacco or drink alcohol, it may increase the risk of lung cancer among those who do smoke or drink. Few studies have investigated the action of beta-carotene supplements in preventing other types of cancer, and this is the first major study focusing on beta-carotene supplements and colorectal cancer.
RESEARCH: Researchers tracked the risk of adenoma recurrence for four years in 864 subjects who previously had a cancerous colorectal adenoma removed and were free of polyps at the onset of the study. A total of 707 subjects completed follow-up exams and provided smoking and alcohol use data. After 3 months on placebo, subjects received daily either beta-carotene supplements (25 mg), a combination of vitamin C (1,000 mg) and vitamin E (400 mg), a combination of beta-carotene, vitamin C and vitamin E or placebo.
RESULTS: The researchers wrote, "Among subjects who neither smoked cigarettes nor drank alcohol, beta-carotene was associated with a marked decrease (44 percent) in the risk of one or more recurrent adenomas."
However, there was a modest increase in adenoma recurrence in subjects who smoked cigarettes (36%) or drank alcohol (13%). Those who smoked and consumed more than one alcoholic drink daily had a substantial increase (107%) in adenoma recurrence. In general, the findings are consistent with a study showing that patients with colon polyps had low tissue levels of carotenoids. (See the June 2003 VERIS Alert or Muhlhofer A, Buhler-Ritter B, Frank J, et al. Carotenoids are decreased in biopsies from colorectal adenomas. Clinical Nutrition, 2003;22:65-70.)
IMPLICATIONS: This study found that people at risk for recurrence of colorectal cancer benefited significantly from beta-carotene supplements if they did not smoke or drink alcohol. However, smoking or a combination of smoking and regular alcohol consumption increased the risk of adenomas. The researchers warned, "Our data suggest that ethanol [alcohol] intake may counter a protective effect of beta-carotene on neoplasia in the bowel."
These findings should encourage patients to stop smoking and drinking.
Baron JA, Cole BF, Mott L, et al, "Neoplastic and antineoplastic effects of beta-carotene on colorectal adenoma recurrence: results of a randomized trial," Journal of the National Cancer Institute, 2003;95:717-722.
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