Selenium (Se), an essential trace element, is of fundamental importance to maintain proper health in both animals and humans. It is a powerful antioxidant mineral and is found in all tissues of the body.
Research suggests that apart from being relevant to human health, selenium is also found to play essential role in maintaining several metabolic processes, such as regulation of thyroid hormone metabolism and protection against oxidative damage to body cells by eliminating peroxides (Briefing Paper, British Nutrition Foundation, 2001).
Although very small quantities of selenium are required for a person to maintain proper health, the amount of selenium that one needs every day depends on age. Hence, average daily recommended dose for adults is 55 µg/day (NIH, 2016).
The biological effects of selenium are predominantly linked to selenium-containing proteins (selenoproteins), which represent diverse molecular pathways and biological functions, including protection against oxidative stress. Hence, deficiency of selenium may lead to altered function of the selenoproteins, which further leads to various pathophysiological conditions like cardiovascular and neuromuscular diseases, cancer, male infertility, inflammation and other free radical-related problems, such as premature ageing (Lebunskyy et al., 2014).
Selenium must be obtained through dietary sources as most selenium comes from the soil, through plants. Levels of selenium available in soils are highly variable globally. Areas that are notably low in selenium include parts of China, Siberia, Central Africa, Eastern Europe and New Zealand.
Human selenium status is sensitive to changes in the food supply, a major route of exposure for most people. Hence, any geographical differences (e.g. fossil fuel burning with release of sulfur, an selenium antagonist, acid rain, soil acidification and use of high-sulfur fertilizers) in the availability of the selenium in soil for uptake by plants may influence its content in the food.
Some common dietary foods that contain selenium in various forms include garlic, Brazil nuts, mushrooms, asparagus, wheat and many cereals. An ideal nutritional supplement would be a selenium-enriched edible plant part, wherein the selenium metabolically accumulates in the form of bioavailable organic selenium compounds. Plants that naturally contain higher levels of the sulfur-containing amino acids, such as those from the Allium and Brassica species are preferred for enrichment, based on metabolic criteria (Perrone et al., 2015).