Vitamin supplements do not cut risk of gastrointestinal cancerBMJ 2004; 329 doi: https://doi.org/10.1136/bmj.329.7470.817 (Published 07 October 2004) Cite this as: BMJ 2004;329:817
Supplements of antioxidant vitamins do not reduce the risk of gastrointestinal cancers, and some may be associated with an increased risk of death, concluded a systematic review published last week.
The Cochrane Hepato-Biliary Group reviewed all randomised trials that compared antioxidant supplements with placebo for the prevention of gastrointestinal cancers. The group assessed the incidence of gastrointestinal cancers, overall mortality, and adverse effects in 14 randomised trials, which comprised a total of 170 525 participants (Lancet 2004;364: 1219-28).
Vitamins A, C, and E; β carotene; and selenium (alone or in combination) had no protective effects compared with placebo on the incidence of oesophageal, gastric, colorectal, pancreatic, and liver cancers. Antioxidant supplements were associated with increased mortality in some trials.
Results from seven studies showed a small but significant increase in mortality with antioxidant supplements (relative risk 1.06, 95% confidence interval 1.02 to 1.10). And a combination of β carotene and vitamin A was associated with a 30% increased risk of death while combined β carotene and vitamin E was associated with a 10% increased risk.
Selenium had a significant beneficial effect on the incidence of gastrointestinal cancer in four trials, although three of these were considered to have unclear or inadequate methodology. The authors suggest that selenium should be studied in randomised trials.
Goran Bjelakovic, from the Cochrane Hepato-Biliary Group, and the University of Niss, in Serbia and Montenegro, said that although they had not found any evidence of a protective effect, only certain antioxidant supplements had been studied. “The results should not be translated to the potential effects of vegetables and fruit, which are rich in antioxidants and other substances,” he cautioned.
In an accompanying editorial, David Forman, professor of cancer epidemiology at the University of Leeds, and Douglas Altman, professor of statistics in medicine in the Cancer Research UK Medical Statistics Group, Institute of Health Sciences, Oxford, wrote, “The simple conclusion from the review is that, apart perhaps for vitamin C and selenium, regular use of antioxidant supplements does not prevent gastrointestinal cancer.” They cautioned that findings of increased mortality with some supplements were only preliminary and warranted further research (Lancet 2004;364: 1193-4).
Patrick Holford, founder of the Institute for Optimum Nutrition, an independent research centre based in London said, “This is one of the most biased and unsubstantiated reports on antioxidants I've ever read.” Some positive studies had been excluded, including a trial of colorectal adenomas, which showed a 50% reduction in recurrence in people taking β carotene or vitamins C and E, he said.