Popular vitamin supplements are swallowed by millions of people in the belief that they will prolong their life expectancy, but according to a new research they may actually be harmful and could increase risk of death.
The review of studies found no evidence that the nutrition supplements extend life.
Antioxidants are nutrients such as vitamin E, vitamin C, or beta carotene that have been marketed as a way to counter the damaging effects of oxygen in the tissues.
In the meta-analysis of 67 randomized studies it was found that supplemental antioxidants do not reduce mortality and that some - including vitamin A, beta-carotene and vitamin E - could increase mortality.
The review combined evidence from more than 200,000 people.
"The harmful effects of antioxidant supplements are not confined to vitamin A. Our analyses also demonstrate rather convincingly that beta-carotene and vitamin E lead to increased mortality compared to placebo," said review co-author Christian Gluud, M.D.
The review included studies of healthy adults and adults diagnosed with specific, stable medical conditions. The authors excluded studies with children or pregnant women, or studies that evaluated supplements as treatment for acute diseases, such as malignant cancer. It also excluded studies that used supplements for replacement of nutrient deficits.
The review authors recommend greater regulation of antioxidant supplements and make a "plea for urgent political action," said Gluud, director of medical science, associate professor and department head of the Copenhagen Trial Unit at the Centre for Clinical Intervention Research and Copenhagen University Hospital in Denmark.
"We should request that the regulatory authorities dare to regulate the industry without being financially dependent on the very same industry," Gluud said.
The study is published in The Cochrane Library, a publication of The Cochrane Collaboration, an international organization that evaluates medical research.