A new study published by The Cochrane Library has placed doubt on both the safety of antioxidants, and their supposed health benefits by finding that several vitamins do not decrease mortality in healthy individuals and that in fact two vitamins, Vitamin A and E, may actually increase mortality.
The researchers, based in Denmark, analyzed the data from 67 clinical trials to determine the effects of five common antioxidant supplements on mortality. The supplements analyzed were vitamin A, vitamin C, vitamin E, selenium, and beta carotene.
In total, 232,550 individuals were analyzed across the studies. A total of 136,023 individuals took supplements while the remaining 96,527 a placebo. Overall 17,880 (13.1%) people taking the antioxidants died while 10,136 (10.5%) of those taking the placebo died. The study found no difference in the effects of the antioxidants in healthy individuals compared to those suffering various diseases.
When analyzing the studies that had the lowest risk of experimental bias, the researchers found that vitamin A appeared to increased the relative risk of death by 16%, vitamin E increased the relative risk of death by 4%, and beta carotene increased the relative risk of death by 7%. The researchers did not find a significant effect of vitamin C on mortality and found that selenium reduced the risk of mortality by 9% however this effect was only weakly significant.
On average, participants across the studies received high levels of the vitamins and minerals, in some cases more than ten times the recommended daily allowance (RDA). The average dose of Vitamin A across the studies was 20,219 IU (the RDA in America is just 2,500 IU). The average dose of Vitamin E was 570 IU (the RDA for Vitamin E is around 25 IU), Vitamin C average dose was 497mg (the RDA for vitamin C is 60mg). The average dose of Beta carotene was 18mg and the average dose of selenium was 99ug (compared to an RDA of 60ug).
The authors urge caution over taking doses of vitamins well in excess of the recommended daily intake, particularly if the person already consumes five or more servings of vegetables a day. Vitamins are essential to the functioning of a healthy body however this doesn’t mean more is necessarily better. Vitamin and mineral supplementation is generally only recommended by health professionals when an individuals diet is lacking in fresh fruit and vegetables and therefore they may not be getting sufficient vitamins and minerals through diet alone.
The researchers also believe that stricter controls are needed in the booming dietary supplements industry which is estimated to be worth more than $20 billion a year.
The research is backed up by a 2005 study on the effects of high dose vitamin E on mortality published in the journal Annals of Internal Medicine. That study found that while mortality decreased slightly for low dosage vitamin E (below 150 IU per day), mortality increased at dosages beyond this level.
Studies have also found that beta carotene can increase the risk of developing prostate cancer. One study also found that beta-carotene increases the probability of developing lung cancer, particularly in those already at high risk such as smokers and those exposed to asbestos.