Ten years ago, free radicals were the leading suspects
in a huge range of diseases. It seemed only a matter of
time before longstanding pathological mysteries would
finally be solved. In the meantime, what could be more
natural than taking antioxidative vitamin E supplements
to combat these nefarious processes? However, study after
study has failed to find a clear benefit from the popular
antioxidant, vitamin E. The supplement's supporters have
pointed to those studies' small sizes and short durations,
but this defence is looking a little weak in light of
a study published March 16 in the Journal of the American
Medical Association (JAMA).
The study, a continuation of the
Heart Outcomes Prevention Evaluation (HOPE) trial, was
neither small nor shortterm. Between 1993 and 1999,
researchers of the HOPE trial followed 9,541 patients,
all of who were at least 55 years old at study outset
and suffered from either diabetes mellitus or vascular
disease. About half of these patients participated in
the latest trial, dubbed HOPE-TOO (HOPE — The Ongoing
Outcomes), which was continued through to 2003. Another
reason for the trial's extension was the emergence of
data from other studies which suggested that vitamin
E might need a long duration of treatment to be effective,
according to lead researcher Dr Eva Lonn from Ontario's
McMaster University.
HO
HUM... OR NOT
No significant differences between the vitamin E patients
(who took 400IU daily of natural source) and the control
group were observed for any of the trial's primary outcomes:
cancer incidence, cancer deaths, and major cardiovascular
events including myocardial infarction, stroke and cardiovascular
death. Relative risk in the vitamin E group was 0.94
for cancer incidence, 0.88 for cancer deaths, and 1.04
for major cardiovascular events. Although none of these
findings show that vitamin E is dangerous, they also
don't even come close to showing a statistically significant
benefit from the supplement.
What was statistically significant,
however, was the increased risk of heart failure and
hospitalization for heart failure in the vitamin E group.
The relative risks of these events were 1.13 (P value
0.03) and 1.21 (P value 0.045) respectively. The P values
here all but eliminate the possibility that random variation
skewed the findings.
POISON
HYPOTHESES
The results serve to illustrate the dangers of relying
on plausible biological mechanisms in the absence of
proper testing. University of Washington instructors
Dr Greg Brown and Professor John Crowley make the point
in an accompanying JAMA editorial: "This report
effectively closes the door on the prospect of a major
protective effect of longterm exposure to this supplement
... In doing so, HOPE-TOO re-emphasizes the importance
of controlled clinical trials for testing important
hypotheses deriving from basic biological findings or
from epidemiological observations. The latter can mislead;
well-designed clinical trials rarely do."
The study authors at McMaster agree,
writing "our findings emphasize the need to thoroughly
evaluate all vitamins, other natural products, and complementary
medicines in appropriately designed trials before they
are widely used for presumed health benefits."
JAMA Mar 16 2005;293(11):1338-47.
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