If you're a man, you can give blood to get this effect. I believe there was a study linking this to a decline in diabetes risk (or something like that).
Excess iron appears to be more of a risk factor for heart disease than diabetes. This is suspected as a reason why pre-menopausal women have a lower risk of heart attack than men and post-menopausal women. This is still an area of active research and not really proven.
Yes, that, too. I was thinking of this, but I think they're all closely related. And hey, even if the science doesn't pan out, you've still probably helped someone out with your donation.
