Antioxidant Pills Don’t Cut Cancer Risk
Selenium May Benefit Men, but More Study Needed
Jan. 24, 2008 -- With one possible exception, many antioxidants in pill form
do not appear to protect against cancer, according to pooled
data from some of the most rigorous studies ever to examine the issue.
There was some evidence linking the mineral selenium to a reduced risk of
cancer in men, but not in women. But the findings are not yet conclusive enough
to recommend that men take selenium supplements, says Mayo Clinic physician Aditya Bardia,
Bardia and colleagues combined 12 clinical trials including more than
100,000 participants for their systematic analysis, which appears in the
January issue of the journal Mayo Clinic Proceedings.
Among their other major conclusions:
- As previously reported, beta-carotene supplementation was found to be
associated with an increased risk of cancer in smokers and a trend toward
increased death rate from cancer.
- Taking vitamin E supplements appeared to be of little benefit or harm with
regard to cancer risk.
"Because we were able to pool the results from several different
studies, we were able to show associations that individual studies might not
show," Bardia tells WebMD.
Beta-Carotene and Lung Cancer
The analysis included two widely reported clinical trials published in the
mid-1990s designed to determine if beta-carotene lowered lung
cancer risk in smokers when combined with vitamins A or E.
Both studies showed an increased risk for lung cancer in smokers who took
Bardia says the evidence overall is now strong enough to recommend that
smokers avoid beta-carotene supplements.
Based on this evidence, the health advocacy group Center for Science in the
Public Interest (CSPI) last month petitioned the Food and Drug Administration
to require labels on beta-carotene supplements warning smokers about the
"Smokers are already at a high risk for lung cancer, and it appears that
they are at even greater risk if they take beta-carotene supplements," CSPI
senior nutritionist David Schardt tells WebMD. "Smokers need to know this,
and it should be on the labels of these products."
Eat Your Fruits and Vegetables
The analysis did suggest a lower cancer risk in men who took selenium
supplements, but the finding was based on the results of just three trials, and
only one was of high quality, Bardia says.
Findings from two large, ongoing randomized trials assessing selenium
supplementation for the prevention of prostate
cancer should help clarify the issue, he adds.
Bardia also points out that the studies included in the analysis did not
examine whether eating antioxidant-rich foods such as fruits, vegetables, and
whole grains can lower cancer risk.
Many health groups, including the American Cancer Society (ACS), recommend
consuming antioxidants through foods instead of supplements.
"It is an old-fashioned message but it is important to eat a variety of
foods, including plenty of fruits
and vegetables," ACS nutritional epidemiologist Marjorie McCullough,
ScD, tells WebMD. "If people really would do this it would go a long way to
ensuring that they get the nutrients and phytochemicals that may be important
for reducing their cancer risk."