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I suggest you read this article, which suggests that blood donation doesn't decrease mortality.
What do you (or anyone else) think of it?
There is a review floating around where some researchers investigated exactly this claim and concluded that the reverse causation effect only accounted for about 30% of the effect. This is one of those situations where the costs and benefits are a massive enough ratio to make it worth the risk that it isn't doing anything IMO.
I tried to find it but failed. Do you recall it's title or authors?
Sorry I don't. Don't see it with a cursory search in google scholar either.
Oh well. I'll still mention this in Immortality: A Practical Guide if that's okay with you.
Oh if you want to cite it I'll look a little harder.
This review actually seems pretty thorough and reports a negative result (though still positive for people who have already experienced a CHD event): http://circ.ahajournals.org/content/103/1/52.full
They discuss why they think positive results happened in previous studies. I'm updating away from the hypothesis as a result of finding this. Blood donation still has enough other studies showing various benefits and essentially no studies showing harm (except for excessive donation, more than twice a year IIRC) that I think it is worth it, but the mortality effects might not be very high.
Keep in that one of blood donation's supposed mechanisms is to prevent iron overload, but only ~0.5% of the population has iron overload to begin with. See ChrisT's comment.
My post mentions a specific reason -- iron overload -- which is bad for you. Blood donation fixes that problem if it exists.
That particular argument does not rely on correlations at all.
Your post also mentioned that males tend to have iron overload. I find this to be suspect, as if males tended to have iron overload, the study would have probably found that blood donation decreases mortality.
That said, for those who do have iron overload, blood donation likely does fix that.
I don't know how prevalent iron overload is. It might well be rare enough so that its effects are lost in the noise. I wasn't claiming that donating blood is necessarily healthy, my point was rather that mechanisms (not correlations) by which blood donation could be useful for health exist.
If you don't know how prevalent iron overload is, then you can't know that men tend to have it, so I suggest editing you comment to say "some men have iron overload" instead of "men tend to have iron overload."
Iron overload / haemochromatosis occurs in approx 0.5% of the population of Northern European origin (and less in other ethnicities). Undiagnosed and untreated the iron will build up in the liver and other organs and cause a variety of unpleasant side effects. Venesection is the standard treatment, though I suggest that less than 0.5% of the population is not significant enough to explain the other studies.
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