Selenium (Se) is an essential micronutrient with proposed role in the protection
of DNA, proteins and lipids from oxidative damage, and in the homeostasis of the immune
system, thyroid gland and spermatogenesis. Environmental (soil and water) availability
influences Se food content and thus the Se status of the different populations.
Recommended daily intake in USA and Europe is 55 and 60 μg/day, with tolerable upper
intake levels of 400 and 300 μg, respectively. Biological activities are dependent on the
organization of the elemental form in the structure of the amino acids selenomethionine and
selenocysteine, with the latter as functional component of endogenous proteins with role in
redox catalysis (glutathione peroxidases, thioredoxin reductases, and iodothyronine
deiodinases), signaling, storage, transport and structural activities. A series of epidemiology
and intervention studies have suggested that populations exposed to high levels of intake
may benefit of health promoting effects and this has made Se supplements quite popular.
However, such positive effects are not always supported by sufficient evidence and a
number of studies, on the other hand, have suggested that higher intakes may cause adverse
effects increasing the risk of cancer and diabetes. Chronic toxicity of Se remains in fact
matter of concern representing a valid reason for further clinical investigation on the safety
of current supplementation and food fortification protocols. This chapter provides a
systematic analysis of the literature available on these aspects particularly focusing on
nutritional and biochemistry features of Se.
Keywords: Selenoproteins, Selenocysteine, Selenomethionine, Se intake,
Selenosis, Selenium deficiency, Thyroid hormones, Diabetes, Glutathione
peroxidase, Redox catalysis.
