Response: Re: Selenium and Vitamin E: Interesting Biology and Dashed Hope

Extract

Goosens et al. are incorrect when they say that the high selenium yeast used in the NPC trial was only 20% L -selenomethionine. As previously documented in the Journal ( 1 ), as part of the process that lead to the decision to use L -selenomethionine in SELECT, several samples of yeast from the NPC trial were obtained and analyzed for selenium content. The results disclosed a substantial batch to batch variability in overall selenium content, but in all analyses, selenomethionone was the predominant species found. The authors are correct that the results of SELECT do not formally rule out a potential preventative effect of other selenium species, but current understanding of selenium biology suggests that to be active as chemopreventatives, all ingested species must be metabolized to methylselenol ( 2 ). Although different organic forms of selenium may be metabolized to the active species at different rates, in the end, their cellular effects are mediated by the same metabolite. Given that SELECT had a cumulative exposure of more than 78 000 person-years to active organic selenium, it seems unlikely that use of a different species would yield substantially different results.