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[SANET-MG] a study on vitamins and cancer
The article below is interesting. Vitamin A and beta carotene seem to
cause problems and that is something to remind the GM people. Selenium
seems stellar in this study.
Volume 364, Issue 9441 , 2 October 2004, Pages 1219-1228 Lancet
Antioxidant supplements for prevention of gastrointestinal cancers: a
systematic review and meta-analysis
Goran Bjelakovic, MD, , a, b, Dimitrinka Nikolova MAa, Rosa G Simonetti,
MDa, c and Christian Gluud, MDa
a The Cochrane Hepato-Biliary Group, Copenhagen Trial Unit, Centre for
Clinical Intervention Research, Copenhagen University Hospital, H:S
Rigshospitalet, Copenhagen, Denmark
b Department of Internal Medicine—Gastroenterology and Hepatology,
Medical Faculty, University of Nis, Nis, Serbia and Montenegro
c Divisione di Medicina, Ospedale V Cervello, Palermo, Italy
Background Oxidative stress can cause cancer. Our aim was to establish
whether antioxidant supplements reduce the incidence of gastrointestinal
cancer and mortality.
Methods With the Cochrane Collaboration methodology, we reviewed all
randomised trials comparing antioxidant supplements with placebo for
prevention of gastrointestinal cancers. We searched electronic databases
and reference lists (February, 2003). Outcome measures were incidence of
gastrointestinal cancers, overall mortality, and adverse effects.
Outcomes were analysed with fixed-effect and random-effects model
meta-analyses and were reported as relative risk with 95% CIs.
Findings We identified 14 randomised trials (n=170 525). Trial quality
was generally high. Heterogeneity of results was low to moderate.
Neither the fixed-effect (relative risk 0·96, 95% CI 0·88–1·04) nor
random-effects meta-analyses (0·90, 0·77–1·05) showed significant
effects of supplementation with -carotene, vitamins A, C, E, and
selenium (alone or in combination) versus placebo on oesophageal,
gastric, colorectal, pancreatic, and liver cancer incidences. In seven
high-quality trials (n=131727), the fixed-effect model showed that
antioxidant significantly increased mortality (1·06, 1·02–1·10), unlike
the random-effects meta-analysis (1·06, 0·98–1·15). Low-quality trials
showed no significant effect of antioxidant supplementation on
mortality. The difference between the mortality estimates in
high-quality and low-quality trials was significant (Z=2·10, P=0·04 by
test of interaction). -carotene and vitamin A (1·29, 1·14–1·45) and
-carotene and vitamin E (1·10, 1·01–1·20) significantly increased
mortality, whereas -carotene alone only tended to increase mortality
(1·05, 0·99–1·11). In four trials (three with unclear or inadequate
methodology), selenium showed significant beneficial effect on the
incidence of gastrointestinal cancer.
Interpretation We could not find evidence that antioxidant supplements
can prevent gastrointestinal cancers; on the contrary, they seem to
increase overall mortality. The potential preventive effect of selenium
should be studied in adequate randomised trials.
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