IS NUTRITIONAL SELENIUM COMPROMISED BY BIOAVAILABLE TOXIC TRACE ELEMENTS -- AND WHERE

Selenium (Se) is an essential micronutrient found in over 20 categories of human seleno-proteins. Many of the Se-proteins are enzymes, with Se as the active center of these catalysts. Major attributes of these molecules are as antioxidants and immuno-enhancement regulators. These characteristics are impaired in people with low Se status, which correlates with a spectrum of viral infections ranging from Keshan coxsackie virus B3 disease causing cardiomyopathy, to Hepatitis (B and C), and HIV-AIDs. Further, Se is increasingly acknowledged for its chemopreventive properties. The US Recommended Daily Allowance for Se is 55 mcg per day for women and men, and the UK Reference Nutrient Intake is suggested at 60 mcg Se per day for women and 75 mcg Se per day for men. Clinical trials, however, indicate that chemoprevention occurs at 200 mcg Se per day, and immune enhancement increases with as much as 600 mcg Se per day.

Despite these recommended dietary allowances, the average daily intake of Se in most European counties ranges between 11-70 mcg per day. Se initially enters the diet through soils. General diets in the US contain 55 mcg Se per day or more, based on high-Se soils of the Northern Great Plains and on agricultural supplements. Less is known, however, about the bioavailability of Se from soils in Africa, Asia, Central and South America. Increasingly recognized is that Se bioavailability through foodstuffs grown without supplemental Se is decreasing with increasing soil acidity.

Beyond Se status, numerous dietary trace elements behave antagonistically to nutritional Se. An example is arsenic (As): Se and As are mutually excreted in bile as seleno-bis(S-glutathionyl) arsinium ion, [(GS)2AsSe]-. Despite other toxic effects, other trace elements, such as antimony, cadmium, gold, mercury, silver and tin, might have similar mutual Se depletion mechanisms. Geochemical mapping of soils on a world-wide basis could help to determine nutritional status of soils and the health of their subsistence populations and may help to address nutritional causes of various diseases.