Selenium is an essential trace mineral that is incorporated into a number of important selenoproteins in the body, such as selenoprotein P, glutathione peroxidase, iodothyronine deiodinase, thioredoxin reductase and selenoprotein W. A full clinical deficiency of selenium is rare and leads to the childhood cardiomyopathy called Keshan disease. However, sub-clinical deficiency of selenium is relatively common, and manifest itself as a decrease in the expression of the selenoproteins which results in subtle defects in cellular metabolism. Selenium intakes have been researched and many populations in the world found to have suboptimal intakes, resulting in sub-clinical deficiencies. Supplementation of selenium at 200 µg per day in the form of selenium yeast has been shown to reduce the chance of developing all types of cancer by 50 %, highlighting this widespread sub-clinical deficiency.
Research published in the American Journal of Clinical Nutrition in 20051, demonstrated that supplementation of 37 µg /d of selenomethionine, or 66 µg / d of selenite was able to achieve full expression of plasma glutathione peroxidase in Chinese subjects with normal daily intakes of selenium of around 10 µg / d. This study was conducted in the Mianning County region of China which is known to have selenium deficient soils. However, at these intakes subjects were still unable to fully express selenoprotein P. These data suggest that the organically bound selenomethionine is a superior form of selenium supplement because it has better bioavailability than the inorganic selenite. Further, it would appear that selenoprotein P is a superior indicator of selenium status than glutathione peroxidase, because higher intakes of selenium are needed to fully express the selenoprotein P protein.
Addition of sodium selenate to fertilisers in selenium deficient soils has been reported in the literature as effective in improving selenium intakes in populations. For example research published in the American Journal of Nutrition in 19882, demonstrated that use of selenium rich fertilisers on agricultural soils was effective at raising the selenium concentration of foods grown on normally deficient soils. Eating these foods raised the selenium urine concentrations of the local populations suggesting they had improved selenium intakes. Supplementation is an important component of optimal health because intakes are difficult to achieve from conventional foods. These data above tend to suggest that seleniomethionine is a more absorbable form than the inorganic selenite. Selenomethionine is available in tablets as ‘selenium yeast’, and is the recommended form of selenium because it is the form most often used in research studies.
RdB
