Essential trace element necessary for the functioning of the glutathione-peroxidase enzyme system that protects cellular structures from oxidative damage. It is obtained from foods such as vegetables, cereals, legumes, garlic, fish, seafood, eggs and meat. The amount of selenium in these sources depends on the concentration of selenium in the soil. The brazil nut (Bertholletia excelsa) is the food with the highest known concentrations of selenium. Selenium deficiency is very rare. With a staple diet it is not necessary to take selenium supplements in the absence of disease or a condition that may warrant it: parenteral nutrition, Crohn's disease, prematurity (MedlinePlus 2017). Taking too much selenium can cause selenosis, a condition that causes dermatological symptoms (alopecia, nail dystrophy), digestive symptoms, neurological symptoms and fatigue (MedlinePlus 2017).Nutritional supplements containing excessive amounts of selenium have resulted in severe poisoning (Aldosary 2012, Senthilkumaran 2012).The potential effects of selenium on cancer prevention, cardiovascular disease, and heavy metal poisoning and toxins are not proven, so supplementation of selenium other than from normal diet is not recommended (MedlinePlus 2017). The daily needs of selenium for breastfeeding mothers are 70-75 micrograms (mcg) daily. In infants it is 2 to 3 mcg/kg (10 mcg/day during the first 4 months) with a maximum of 30 mcg/day (MedlinePlus 2017, Kipp 2015). Selenium is found naturally in milk in its organic form of selenomethionine (Dorea 2002). The amount of selenium in colostrum is 80 mcg per litre and in mature milk 12-20 mcg/L, with no or very weak correlation with plasma selenium levels or daily intake of selenium (Wasowicz 2001, Bianchi 1999, Artaud 1993, Cummings 1992, Levander 1987, Higashi 1983). However, there are authors who find that selenium supplements for breastfeeding mothers increase selenium levels in milk and infants may exceed their daily needs for selenium. (Dorea 2002, Trafikowska 1996). Better plasma levels of selenium have been found in breastfed infants than in formula-fed infants (Strambi 2004, Sorvacheva 1996). There are lower plasma levels of selenium in babies born small for their gestational age (Strambi 2004).