A review of the scientific evidence for the National Cancer Institute finds little support for marketing dietary supplements as protection against cancer-and notes that high doses of some supplements can actually add to cancer risk. Most clinical trials of vitamin and mineral supplements against cancer have disappointed, the reviewers concluded. In the review, except for a lone Chinese study, trials of antioxidant supplements, including beta-carotene and vitamins C and E, failed to show anti-cancer benefits. Results for long-term folic acid supplementation versus cancer have likewise been mostly negative. Although some epidemiological studies have linked higher vitamin D levels to lower rates of certain cancers, the review found the evidence insufficient and called for more research on vitamin D. Despite the absence of evidence that supplements prevent cancer (and the possibility of harm), reviewers noted that marketing claims by the supplement industry continue to imply anti-cancer benefits. They blamed insufficient government regulation of the $30 billion-a-year industry.
TO LEARN MORE: Journal of the National Cancer Institute, online first, dx.doi.org/10.1093/jnci/djs195.