Selenium is an essential trace mineral required for the formation of a number of selenoproteins. The most well known and well researched selenoprotein is glutathione peroxidase. Glutathione peroxidase is an enzyme that is involved in the reduction of hydrogen peroxide to water and the reduction of lipid hydroperoxides to alcohols, and in this way glutathione peroxidase reduces the oxidative stress in cells. As oxidative stress is implicated as a causative agent in disease, high cellular levels of glutathione are increasingly being seen as beneficial to health. The metabolism of selenium is complex and a number of routes of metabolism and excretion are thought to exist. One such pathway includes the reduction of selenium to selenide with the subsequent formation of methylated selenides, which are then excreted in the urine. One of the know methylated selenium compounds from this pathway is trimethylselenonium ion (TMSe). Using this biomarker, researchers have shown that variation exists in the amount of TMSe excreted in urine.
For example, one group of researchers1 investigated the excretion of selenium in pregnant women and their 5 year old children in a selenium poor area of Bangladesh. The results of the study showed that TMSe producers (those who produced large amounts of TMSe’s during selenium metabolism) were prevalent within the study population and accounted for about one third of the subjects. Produces had around 10 to 70 % of urinary selenium as TMSe, whereas non-produces only had around 0.59 % of the urinary selenium as TMSe. Women with high levels of TMSe in their urine had higher levels of total selenium in their urine, indicating they may be metabolising and excreting higher amounts of selenium. These results show there is a large variation in the excretion of selenium between individuals. This highlights the difficulty in making recommendations for nutrient intakes for selenium. Clearly if metabolism and excretion pathways differ, dietary needs for selenium may also differ between individuals.
Dr Robert Barrington’s Nutritional Recommendation: Studies investigating the protective effect of selenium on cancer suggest that 200 μg of selenium may be required for these protective effects. However, the recommended governmental intake in most Western countries is much lower. The metabolism of selenium is complex and not fully understood, and yet selenium even in amounts many times the recommended intake is safe. The exemplary safety record for supplemental selenium, coupled with difficulties in assessing individual requirements, suggest that taking the upper limit of selenium is a rational approach to ensure that the benefits of selenium are obtained. Most studies that have investigated selenium have used the yeast form, which is also available as selenomethionine. It would therefore seem prudent for those wishing to benefit from the health effects of selenium to take at least 200 μg of selenium per day. Obtaining selenium from food is possible, but it would be impossible to know the amount ingested.
RdB
