Selenium is well absorbed from food with absorption rates being reported to range from 44 to 70%. The high absorption rates of selenium means that optimal selenium status is achievable from food if a high quality diet is consumed. However, this is only the case if the selenium content of the food is adequate, and this can vary greatly depending on the selenium content of the soil that the food was grown in. For this reason animal sources of selenium can be more reliable than plant alternatives. The current United Kingdom recommended nutritional intake for selenium is 75µg/d for men and 60µg/d for women, with the EU recommended daily amount being 55µg/d. The US RDA is 70µg/d for men and 55µg/d for women. New Zealand has low selenium soils and as a result the population has difficulty in achieving adequate selenium status, with intakes typically being less than 30µg/d.
Because of the typically low selenium status of the New Zealand population, researcher1 have investigated the effects of selenium supplements on the glutathione peroxidise (GPx) activity and selenoprotein P activity in healthy New Zealanders, to estimate a daily requirement. Fifty two subjects with low baseline selenium status (<1.26 mmol/L whole blood selenium) were administered selenomethionine supplements at 10. 20, 30 or 40µg/d for 20 weeks. The results showed that at 20 weeks, the mean plasma selenium concentrations had increased by 4, 14, 23, 26, and 41% compared to the control, in the 10, 20, 30, and 40µg/d groups, respectively. Whereas plasma GPx activity increased by 13, 17, 19, 21 and 30% in the 5 groups, respectively. Selenoprotein P concentrations increased during the first 4 weeks of supplementation by 24, 45, 31, 52, and 88% in the 5 groups, respectively.
The plasma selenium concentration needed to achieve full expression of plasma GPx activity was ≈1.14 mmol/L, compared to 1.05–1.10mmol/L for selenoprotein P. This supports other data (here) to show that selenoprotein P is more sensitive marker for selenium status than plasma GPx activity. Large variations occurred between subjects with respect the GPx activity following supplementation, which makes recommendations from clinical data to the general population difficult. Individuals therefore appear to have their own optimal GPX activity probably due to a combination of environmental and genetic variables. Based on the plateau in GPX activity in the 40 µg/d and the average daily intake of New Zealand adults of 30 µg/d the authors concluded that the total required for optimal GPx activity was 70 µg/d, which calculated as a recommended intake of 90 µg/d selenium. This is higher than both the UK, US and EU recommended levels.
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