An analysis of cancer prevention by selenium

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Abstract
The nutritional functions of selenium (Se) are recognized as being due to a number of Se‐containing proteins. It is not clear, however, whether any of these function in the anti‐tumorigenic effects of Se most of which have been demonstrated for Se exposures greater than those required for selenoprotein expression. Indeed, other anti‐tumorigenic mechanisms have been demonstrated for certain Se‐metabolites. The Nutritional Prevention of Cancer Trial found supplemental Se (200 μg/day, as Se‐enriched yeast) to be associated with significant reductions in cancer risks in subjects with pre‐treatment plasma Se concentrations below ca. 120 ng/ml (1.5 nmoles/ml), which level would appear to require food‐Se intakes of ca. 1.5 μg/kg body weight/day. However, the putative anti‐carcinogenic Se‐metabolite(s) should be more relevant than total plasma Se as a supplementation target for cancer prevention. These may be components of the non‐protein‐bound fraction of Se in plasma, which constitutes 2–4% of total plasma Se.