>
> The Lancet: Volume 364, Number 9441 02 October 2004
>
> Antioxidant supplements for prevention of gastrointestinal
> cancers: a systematic review and meta-analysis
>
> Goran Bjelakovic, Dimitrinka Nikolova, Rosa G Simonetti,
> Christian Gluud
>
> Summary
>
> Background Oxidative stress can cause cancer. Our aim was to
> establish whether antioxidant supplements reduce the
> incidence of gastrointestinal cancer and mortality.
>
> 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.





Here is another view by the head of the British Institute for Optimal
Nutrition....Hollford writes..

> In my opinion this is one of the most biased and
> unsubstantiated reports on antioxidants I've ever
> read. If you look at the actual results of this
> supposed comprehensive analysis of research you will
> see that the only really significant finding in a
> considerable reduction in gastrointestinal cancer risk
> with selenium supplementation. Overall, it shows that
> antioxidant supplements reduce the risk of oesophageal
> cancer, have little effect on pancreatic or
> oesophageal cancer, and slightly increase the risk of
> gastric cancer. Overall, the clear trend is towards
> protection, not harm. I believe this is an
> underestimation of the prevention power of
> antioxidants because this claimed comprehensive
> analysis of research excludes some very well designed
> positive studies, such as a trial of 864 people with a
> history of colorectal adenomas, by the National Cancer
> Institute (1). The participants were given either 25mg
> of betacarotene and/or both 100mg of vitamin C and
> 400mg of vitamin E, versus placebo. While there was
> approximately a halving of recurrence of colorectal
> adenomas in those who took either the betacarotene or
> vitamin C and E or both, there was a modest increase
> in cancer recurrence among those who only took
> betacarotene supplements and both smoked and drank
> alcohol every day. Why was this trial excluded?
> Perhaps it didn't give the results the researchers
> wanted.
>
> The final table in the Lancet study, which is the only
> one showing a small negative overall effect on
> mortality (the difference between 1 in 14 cancer
> patients on antioxidants, versus 1 in 15 cancer
> patients), was arrived at by removing any positive
> studies on the grounds of 'low methodological
> quality', leaving only 7 studies out of the original
> 167 studies! Of these studies, one is quoted as
> showing a massive increased risk. Without this study
> there is no such effect. However, this study actual
> showed the exact opposite. The study in question,
> Correa et al (2), published in the Journal of the
> National Cancer Institute, gave people with gastric
> cancer either beta-carotene, vitamin C or
> anti-Helicobacter Pylori treatment (gastric cancer is
> increasingly being thought to be initiated by H.Pylori
> infection, not antioxidant deficiency). All three
> interventions produced highly significantly
> improvements, causing substantial regression of
> gastric cancer. The authors conclude "dietary
> supplementation with antioxidant micronutrients may
> interfere with the precancerous process, mostly by
> increasing the rate of regression of cancer precursor
> lesions, and may be an effective strategy to prevent
> gastric carcinoma." (see abstract below).
>
> So, how could this study bias the results towards
> increased mortality? For the simple reason that six
> people out of 368 treated with antioxidants died, many
> of whom were smokers, compared to none out of 117
> people treated with anti- H.Pylori treatment died! The
> most logical explanation for this finding is that, by
> virtue of participating in this trial, these patients
> were excluded from taking anti- H.Pylori treatment,
> which is highly recommended for gastric cancer. It is
> highly unlikely that the antioxidants had anything to
> do with it. The authors of this study make no
> reference to the possibility of antioxidants
> increasing mortality risk, instead concluding that
> both beta-carotene and vitamin C reduce risk.
>
> A review of the Lancet study (also published in the
> Lancet) by David Forman and Douglas Altman of the
> Centre for Epidemiology and Biostatistics says "The
> mortality analysis in this review does not offer
> convincing proof of hazard." In my opinion this is the
> most atrocious piece of biased number crunching, and
> I'm surprised that the Lancet published it. The
> funding source for this trial should be seriously
> investigated, just to check it is not as biased as the
> rhetoric. Drug companies have a lot to gain by
> discrediting nutritional treatments and I have no
> doubt that there is an orchestrated campaign under way
> to do just this. I certainly won't be stopping my
> daily antioxidant supplement, although I wouldn't
> advise heavy smokers to supplement beta-carotene on
> its own. I would advise people wanting to reduce their
> cancer risk to supplement 50 to 150mcg of selenium,
> together with other antioxidant nutrients."
>
> Patrick Holford.
>
> References
>
> 1 Baron, J et al., 'Neoplastic and antineoplastic
> effects of beta-carotene on volorectal adenoma', J
> Natl Cancer Inst. 95, 10, pp. 717-22 (2003).
>
> 2 Correa P et al., 'Chemoprevention of gastric
> dysplasia:randomised trial of antioxidant supplements
> and anti-helicobacter pylori therapapy', J Natl Cancer
> Inst. 2000 Dec 6;92(23):1881-8.
>

[Thanks for posting this. I had already seen it and basically agree with it. I
simply did not wish to do the analytical work necessary to reach the same
conclusions. My comments were different - of a general nature - and do not
disagree at all with those given above. --Paul]