Selenium occurs in different forms, such as selenocysteine or selenomethionine, in proteins where sulfur is replaced by selenium in their respective sulphurous amino acids. It can be considered as an antioxidant as it allows the formation of glutathione peroxidase enzyme (GSHpx) and prostaglandine. It is involved in the production of tyroid hormons (triiodothyronine) from tiroxine and it has a favorable effect on the immune system, as it increases T lymphocytes and natural killer cells. It also detoxifies from arsenic, cadmium, and mercury (Whanger, 1992; Zwolak, 2012).
Over the last few years, several studies have investigated the relationship between selenium absorption and a reduction in the incidence of cardiovascular diseases, neurologic disorders (such as dementia and Alzheimer) and aging macular degeneration. A recent Cochrane review (Rees, 2013) proved that there is no positive relationship between selenium and CVD, at least for individuals with proper dietary selenium intakes. This review, however, highlighted an increase in the risk of type 2 diabetes. On the other hand, according to other recent trials (PRECISE, PREvention of Cancer by Intervention with SElenium), a six-month selenium supplementation didn't have any diabetogenic effect in elderly people (Rayman, 2013).
Selenium bioavailable forms are preferable for fortification. For example Alesco's Ultrasel®, consisting in sodium selenate liposomal dispersed in sucresters, or, alternatively, organic selenium forms in yeast. Lalmin® Selenium yeast (Lallemand) is composed of inactive Saccharomyces cerevisiae cells, with a high selenomethionine quantity. The selenium organic form is obtained from yeast fermentation, and it can be used to feed cattle to obtain a natural enrichment of derived food (milk, meat) (EFSA, 2011; EFSA, 2012; Phipps, 2008).