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Selenium yeast
Selenium yeast, produced by fermenting ''Saccharomyces cerevisiae'' in a selenium-rich media, is a recognized source of organic food-form selenium. In this process, virtually all of the selenium structurally substitutes for sulfur in the amino acid methionine thus forming selenomethionine via the same pathways and enzymes that are used to form sulfur-containing methionine. Owing to its similarity to S-containing methionine, selenomethionine is taken up nonspecifically and becomes part of yeast protein. It is this metabolic route that makes selenium yeast valuable in animal and human nutrition, since it offers the same organic form of selenium produced by food-chain autotrophs (i.e., most plants and certain blue-green algae).〔
==Human health applications==
Selenium is physiologically essential and may also offer a protective effect against several degenerative diseases. The organic form of selenium provided by selenium yeast has been shown to differ in bioavailability and metabolism compared with inorganic (e.g., selenate, selenite) forms of dietary selenium.〔Schrauzer G. Selenomethionine: A review of its nutritional significance, metabolism and toxicity" ''J Nutr'' 2000;130:1653-1656.〕 Dietary supplementation using selenium yeast has been associated with increased ability to counteract oxidative stress. Furthermore, selenium yeast has been used in a wide range of studies aimed at examining the importance of selenium status in the incidence and progression of a variety of infectious and degenerative diseases.
*Cancer. Although selenium is promoted for its claimed anti-cancer effect, there is no good evidence of it being helpful in treating or preventing cancer, or with helping alleviate the side-effects of cancer treatment. Dietary supplementation with selenium yeast has been used to study the effects of selenium status and the risk of developing cancers or precancerous lesions.〔Combs GJ, Lu J. Selenium as a cancer preventive agent. In: Hatfield D, Berry M, eds. Selenium: Its molecular biology and role in human health, 2nd ed. New York: Springer, 2006: 249-264.〕
*Viral infection. Findings of increased viral virulence in selenium-deficient hosts support the need for further investigation into the interaction between host nutrition and viral evolutionary processes.〔Beck M. Selenium and viral infections. In: Hatfield D, Berry MJ, Gladyshev VN, eds. Selenium: Its molecular biology and role in human health, 2nd ed. New York: Springer, 2006: 287-298.〕 Certain viral diseases have been shown to mutate more rapidly in selenium-deficient hosts producing more virulent viruses. This etiology has been demonstrated for both the Coxsackie B virus (associated with a Se-deficiency-related cardiomyopathy known as Keshan disease) and the influenza virus. High selenium yeast supplementation (200 μg/d) was evaluated in a 9-month double-blind, randomized, placebo-controlled trial in HIV-positive adult men and women. Daily supplementation was found to suppress progression of HIV-1 viral burden and provide indirect improvement to CD4 cell counts. (Selenium status diminishes with HIV disease progression; low selenium status has been shown to be a predictor of HIV-related mortality.〔Baum M, Camps A. Role of selenium in HIV/AIDS. In: Hatfield D, Berry MJ, Gladyshev V, eds. Selenium: Its molecular biology and role in human health, 2nd ed. New York: Springer, 2006: 299-310.〕 Selenium deficiency has also been linked with increased infectiousness of people with HIV-1. )
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