The Pharmaceutical Journal
Vol 273 No 7320 p506
9 October 2004

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Evidence of harm from antioxidant supplements

Antioxidant supplements are not effective in protecting against gastrointestinal cancers, a review of trial data has revealed. What is more, the analysis showed that some combinations of supplements may slightly increase cancer risk. Only selenium was shown to be associated with risk reduction (Lancet 2004;364:1219).

Goran Bjelakovic and colleagues, from the Cochrane hepato-biliary group at Copenhagen University Hospital, examined data from 14 randomised controlled trials involving over 170,000 people — there were 10 different interventions and 2,100 cancer endpoints covering five sites (oesophagus, stomach, large bowel, pancreas and liver). In general, the researchers observed no evidence of benefit or harm when all five cancer sites were considered. The exceptions were vitamin C (for which there were limited data) and selenium, which seemed to exert a protective effect for gastrointestinal cancer.

In terms of harm, two combinations of supplements were found to be associated with increased mortality: beta-carotene and vitamin A (relative risk 1.29, 95 per cent confidence interval 1.14–1.45) and the combination of beta-carotene and vitamin E (1.10, 1.01–1.20).

Writing in an accompanying editorial (ibid, p1193), David Foreman, University of Leeds, and Douglas Altman, Cancer Research UK, say: “Somewhat chillingly, Bjelakovic and colleagues also estimate that, despite the small size of the relative risk, if their findings are correct, 9,000 in every million users of such supplements will die prematurely as a result. The prospect that vitamin pills may not only do no good but also kill their consumers is a scary speculation given the vast quantities that are used in certain communities.”

However, they warn that the analysis is a work in progress and that the mortality findings should be seen as preliminary. “In the event that a hazard is established from a complete review, these researchers will need to identify which specific interventions are associated with any risk.”