Antioxidant Supplements Up Death Risk
Study Shows No Benefit, Slightly Higher Death Risk for Antioxidant Supplements
Antioxidant Supplements and Death Risk continued...
However, some of the trials were more exactly controlled than others. There
were 21 trials that had a "high bias risk." These trials had one or
more problems with randomizing study participants to the supplement or placebo
groups, with blinding both the participants and the investigators to whether
participants received supplements or placebos, and/or with following up on all
participants until the end of the study.
So the researchers looked only at the 47 "low-bias-risk" studies --
which included nearly 181,000 participants and which did not include people
taking selenium. They found that:
- Taking vitamin A supplements increased the risk of death by 16%.
- Taking beta-carotene supplements increased the risk of death by 7%.
- Taking vitamin E supplements increased the risk of death by 4%.
- Taking vitamin C supplements did not have any effect on risk of death.
Shao says it just isn't fair to study antioxidants in this way.
"What these authors have done is combine studies that are incredibly
dissimilar in all sorts of ways," he says. "These studies looked at
different nutrients at different doses at different durations with different
lengths of follow-up -- and in different populations, ranging from folks who
were incredibly healthy to people with cancer and other diseases."
Moreover, Shao says, the researchers looked only at studies in which people
died. That left out 405 clinical trials, which he says skews the results in
favor of death risk. And he points out that the researchers original 68 studies
did not show any harm from supplements.
"These questions cause one to step back and wonder if the findings are
relevant to the healthy population that uses these supplements to maintain
health and avoid chronic disease," Shao says. "That is a point they
don't make: that antioxidants are not used to treat cancer or heart disease.
They are used for disease prevention."
Edgar R. Miller III, MD, PhD, associate professor of medicine at Johns
Hopkins University, in 2004 analyzed clinical trials of vitamin E. He found
that high doses of vitamin E did more harm than good. Miller has high praise
for the Bjelakovic/Gluud study.