Selenium has become one of the most exciting nutrients of the 1970s and 1980s. Once classified solely as a toxic mineral, it is now regarded as an essential one, needed in small daily amounts. Selenium functions as a component of the enzyme glutathione peroxidase, which accounts for its antioxidant function and thus its important contribution to the prevention of the twentieth-century plagues, cancer and cardiovascular disease.
Low soil levels of selenium are associated with higher cancer rates, and soil-rich areas have below-average cancer rates for a number of body systems, particularly the breasts, colon, and lungs. Keshan disease, a form of heart disease prevalent in children and is characterized by an enlarged heart and congestive heart failure, may be a direct result of selenium deficiency, as it has responded well to selenium treatment. People in Keshan, China, where the disease was discovered, treat it with a common herb called Astragalus, which accumulates selenium from the soil.
As in the Keshan area of China, the soil in many parts of the United States is very low in this important mineral. Here, the western states generally have higher selenium levels than the eastern; South Dakota has the highest and Ohio the lowest. Ohio has more than twice South Dakota's rate of a number of common cancers. Most states with high levels of soil selenium show a decreased rate of cancer deaths. There is some concern, though, that high amounts of selenium, particularly elemental selenium and inorganic sodium selenite, may be toxic in areas where it is found in high concentrations in the water and soil, such as South Dakota.
Selenium and vitamin E work together synergistically in that they carry out antioxidant and immunostimulating functions better together than individually; however, their mechanisms of action are probably not the same. Both of these nutrients are part of the "antiaging" or "longevity" group, which may be directly attributable to their antioxidant functions because tissue oxidation by free radicals may be the contributing factor to degenerative disease.
Despite its importance, there is less than 1 mg. of selenium in our body, most of it in the liver, kidneys, and pancreas and, in men, in the testes and seminal vesicles. Men have a greater need for selenium, which may function in sperm production and motility. Some selenium is lost through the sperm as well as through the urine and feces. It is absorbed fairly well from the intestines, with an absorption rate of nearly 60 percent.
Sources: Soil levels of selenium vary greatly from state to state and even within local regions across the United States, as well as from country to country throughout the world. So the amount of selenium in our food sources, whether consumed directly as plants or as meat from animals that have eaten the vegetation, varies according to the soil levels. Further, most selenium in foods is lost during processing, such as when making white rice or white flour.
Many natural foods contain selenium, mainly an organic form that is much less toxic than sodium selenite and definitely less so than elemental selenium. Selenium may be present in some drinking water, and it is sometimes even added to drinking water where it is deficient. We may see this more in the future as a general disease-prevention measure. Mother's milk usually has several times more selenium than cow's milk. Selenium is also used in some shampoos and skin lotions, and it is possible that we absorb small amounts of selenium from these products.