Industry leaders are challenging a recent study that questions the health benefits of antioxidants.
Scientists working at the University of Copenhagen in Denmark examined previous studies into the effect of supplements on healthy people and those with diseases. Their meta-analysis was published under the auspices of the Cochrane Collaboration, a global independent healthcare research body.
The authors concluded: "We found no evidence to support antioxidant supplements for primary or secondary prevention [of mortality]. Vitamin A, beta-carotene, and vitamin E may increase mortality. Future randomised trials could evaluate the potential effects of vitamin C and selenium for primary and secondary prevention.
"Such trials should be closely monitored for potential harmful effects. Antioxidant supplements need to be considered medicinal products and should undergo sufficient evaluation before marketing."
But the Washington DC-based Council for Responsible Nutrition said the meta-analysis "appears to be a systematic attempt by the authors to publish work that supports their own pre-determined conclusions about antioxidants and the way they should be regulated."
In a rebuttal of the research, it pointed out the researchers had identified 748 studies that could be included in the analysis but then determined there were only 409 "eligible." Of those, they excluded all but 67. This meant their conclusions were based on less than 9% of the totality of available evidence on antioxidant supplementation.
In selecting which studies to use, the researchers excluded any in which no deaths were reported, amounting to 405, said CRN. This begged the question of how it was possible to evaluate whether a substance could prevent mortality when studies demonstrating no harm were automatically excluded.
In addition, said CRN, only all-cause mortality was assessed in the review. As a result, the authors didn't eliminate deaths that may have been caused by accident, homicide, suicide or medical conditions that had nothing to do with supplementation.
Michele Sadler, spokeswoman for the UK-based Health Food Manufacturers' Association, said: "In no way can this review be considered comprehensive. The conclusions also go much further than the scope of the evidence and limitations of the individual studies used."