On 22/05/2004, at 23:24, Arly Helm wrote:

> Finally, there are many reasons that taking megadoses (pharmaceutical
> doses)
> of molecules such as vitamins and minerals may be dangerous which are
> unrelated to simple toxicity.  The lung cancer study is a perfect
> example,
> as Lara points out.  In this case there was no toxicity, and yet
> through
> some mechanism, the subjects in the supplement group actually had worse
> outcomes from their preexisting cancers.

This is an inaccurate characterisation of the CARET study. These
weren't pre-existing cancers; these were people who developed cancer
and died at a significantly higher rate on beta-carotene supplements
than those on placebo. No-one will ever know whether there could have
been microscopic nests of cancer before the supplementation, but there
was no cancer diagnosis at enrolment in the trial. The ATBC study also
enrolled high-risk people without existing cancer, and showed a higher
risk of cancer in those taking carotene.
http://cis.nci.nih.gov/fact/4_13.htm

I'm really not sure what definition of "toxicity" you're using here; it
appears to be a fairly narrow one, and that has the potential to
mislead. Promoting cancer development seems pretty toxic to me!

We don't know whether these results are generalisable to non-smokers,
perhaps not; but I for one will continue eating (and recommending) real
food, and avoiding synthetic vitamin A supplements.

Lara Hopkins

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