What follows is a perfect example of both.
does not even come close to negating the veritable avalanche of data from large
properly done randomized trials. These trials have repeatedly reported a lack of
benefit, or actual harm. Some studies have found that vitamin
supplementation actually increases the risk
of developing coronary disease.
Observational studies are never valid for determining cause
and effect. They can only establish a
coincidental relationship or a trend.
More often than not, these relationships are due to unknown factors, or
are not even real. They are, rather, a
result of flaws in the study—typically poor design, questionable statistical
manipulation, or both.
Second, and just as important, is the design of this study. The mortality data on which the conclusions
are based are inaccurate. This is
because NHANES uses a probability
protocol — an algorithm that picks the most likely match between a
study subject and reports of death from a mortality database. But, probability
protocols are merely models, and this adds further inaccuracy. Worse still, the determination of cause of
death is based on diagnosis coding, which is neither standardized nor
controlled. So, any conclusions about a
potential correlation are necessarily based on weak data.Properly conducted randomized studies have
over and again shown harm from wholesale vitamin supplements.
One needs
only to visit the National Cancer Institute’s website
to learn that none of the nine large prospective randomized trials of
antioxidant supplementation to prevent cancer found any benefit.
Moreover, in many of these studies, supplementation actually caused an increase
in cancers. For example, supplementation of beta-carotene and retinol
(Vitamin A) caused an increase in the
incidence of lung cancer, and an increase in the rate of death from any reason.
This is, of course, counterintuitive to
the majority of Americans who have believed in the “goodness” of vitamins since
childhood.
The bottom line is that all studies are not created equal. Some
are bad, and some are excellent. But there
is always someone more than willing to take advantage of the confusion. Remember, before you rush to the next
nutritional fad, if it sounds too good to be true, it is.
Josh Bloom, Ph.D., is
a former medicinal chemist and the Director of Chemical and Pharmaceutical
Sciences at the American Council on Science and Health. David Seres, MD, ScM,
PNS, is associate professor of medicine in the Institute of Human Nutrition and
director of medical nutrition, Columbia University Medical Center. He is
a member of the medical advisory board at Consumer Reports, and a Columbia
Public Voices fellow with the Op-ed Project
