Abstract
Selenium-enriched yeast (Se-yeast) is a common form of selenium used to supplement dietary intake of this important trace mineral. However, its availability within the EU is under threat owing to concerns expressed by the EC Scientific Committee on Food that Se-yeast supplements are poorly characterised and could potentially cause the build up of selenium in tissues to toxic levels. This review examines the validity of these concerns. Diagrams of the biosynthesis and metabolism of selenium compounds show which species can be expected to occur in Se-yeast preparations. Seyeast manufacture is described together with quality control measures applied by reputable manufacturers. The way in which speciation of Se-yeast is achieved is explained and results on amounts of selenium species in various commercial products are tabulated. In all cases described, selenomethionine is the largest single species, accounting for 54-74% of total selenium. Se-yeast is capable of increasing the activity of the selenoenzymes and its bioavailability has been found to be higher than that of inorganic selenium sources in all but one study. Intervention studies with Seyeast have shown the benefit of this form in cancer prevention, immune response and HIV infection. Of around one dozen supplementation studies, none has shown evidence of toxicity even up to an intake level of 800 μg/d selenium over a period of years. It is concluded that Se-yeast from reputable manufacturers is adequately characterised, of reproducible quality, and that there is no evidence of toxicity even at levels far above the EC Tolerable Upper Intake Level of 300 μg/d.