Some Vitamin Supplements Increase Death Risk Say Researchers

Some Vitamin Supplements Increase Death Risk Say Researchers

28 Feb 2007   

Vitamin supplements taken by millions of people every day for their
health could be increasing their risk of death a new Danish-led study
suggests.

The study is published in the Journal of the American Medical
Association.

The international research team reviewed the published evidence on beta
carotene, vitamin A, vitamin E, Vitamin C and selenium. The team was led
by Dr Goran Bjelakovic, from Copenhagen University Hospital, Denmark.

These dietary supplements are marketed as antioxidants and people take
them in the hope they will improve health and guard against diseases
like cancer and heart disease by eliminating the free radicals that
cause "oxidative stress" and damage and kill off cells.

Antioxidants are also marketed as anti-aging products because they are
thought to slow down the aging process.
Some studies have suggested that antioxidants are beneficial to health,
while others, mostly larger clinical trials, have concluded they have no
effect on health and say in some cases that taking too many of them can
be harmful.

In this study, Dr Bjelakovic and colleagues did a meta-analysis on
research published before October 2005.
Meta-analysis is a way of sifting through published studies against a
quality standard that looks at a number of reliability criteria such as
potential for bias. Then the ones that pass the standard are taken
through a statistical process to find out if they are saying something
consistently reliable. There can be several levels of "sifting", each
producing a more reliable and robust set of evidence.

In this case the researchers followed a method established by the
Cochrane Collaboration, a group of 6,000 health care specialists who
review biomedical trials and other research projects.
They started with 815 clinical trials of which 68 passed the first level
of quality standard. At this level the results were inconclusive. The
supplements were found to have no effect on death risk one way or the
other.

They then went back and eliminated 21 of the trials, leaving only the
"low-bias" ones. This was the next level of quality standard. At this
level of meta-analysis the results were different.

When looked at separately they found that Vitamin A increased death risk
by 16 per cent, beta carotene by 7 per cent and Vitamin E by 4 per cent.
The results for Vitamin C were not so clear, but by looking at the best
quality trials there was a suggestion that it increased death risk by 6
per cent, either on its own or in combination with other supplements.

The figures from the best quality trials on selenium however showed that
it might reduce death risk by 10 per cent, either on its own or in
combination with other supplements, but this was not found to be
statistically significant.

The overall conclusion of the study was that on balance, the best
quality research shows that beta carotene, vitamin A and vitamin E may
increase mortality risk, but vitamin C and selenium need further study.

A spokesperson for the supplements industry said the research was
"flawed" because it included studies conducted on people who were
already very sick.

The researchers say there are several potential reasons for these
results. One is that the free radicals that are thought to cause the
oxidative stress are the byproduct rather than the cause of disease.
Another is that they may play an important role in the immune system and
eliminating them could be counterproductive.

The researchers pointed out that the studies they examined only used
synthetic supplements, and therefore their observations and conclusions
do not apply to natural antioxidants such as those found in fruit and
vegetables.

They added however that this study is important for public health
reasons because between 10 and 20 per cent of people in Europe and North
America take dietary supplements.

Nutritionists say that instead of taking supplements the best way to
protect your health is to eat a balanced diet and to get all the
vitamins you need from your food.

"Mortality in Randomized Trials of Antioxidant Supplements for Primary
and Secondary Prevention; Systematic Review and Meta-analysis."

Goran Bjelakovic, Dimitrinka Nikolova, Lise Lotte Gluud, Rosa G.
Simonetti, and Christian Gluud.
JAMA 2007;297:842-857.
Vol. 297 No. 8, February 28, 2007

Written by: Catharine Paddock
Writer: Medical News Today

Article URL: http://www.medicalnewstoday.com/healthnews.php?newsid=64100


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