Establishing optimal selenium status: results of a randomized, double-blind, placebo-controlled trial

Background: Dietary recommendations for selenium differ between countries, mainly because of uncertainties over the definition of optimal selenium status. Objective: The objective was to examine the dose-response relations for different forms of selenium. Design: A randomized, double-blind, placebo-controlled dietary intervention was carried out in 119 healthy men and women aged 5064 y living in the United Kingdom. Daily placebo or selenium-enriched yeast tablets containing 50, 100, or 200 mu g Se (approximate to 60% selenomethionine), selenium-enriched onion meals (approximate to 66% gamma-glutamyl-methylselenocysteine, providing the equivalent of 50 mu g Se/d), or unenriched onion meals were consumed for 12 wk. Changes in platelet glutathione peroxidase activity and in plasma selenium and selenoprotein P concentrations were measured. Results: The mean baseline plasma selenium concentration for all subjects was 95.7 +/- 11.5 ng/mL, which increased significantly by 10 wk to steady state concentrations of 118.3 +/- 13.1, 152.0 +/- 24.3, and 177.4 +/- 26.3 ng/mL in those who consumed 50, 100, or 200 mu g Se-yeast/d, respectively. Platelet glutathione peroxidase activity did not change significantly in response to either dose or form of selenium. Selenoprotein P increased significantly in all selenium intervention groups from an overall baseline mean of 4.99 +/- 0.80 mu g/mL to 6.17 +/- 0.85, 6.73 +/- 1.01, 6.59 +/- 0.64, and 5.72 +/- 0.75 mu g/mL in those who consumed 50, 100, or 200 mu g Se-yeast/d and 50 mu g Se-enriched onions/d, respectively. Conclusions: Plasma selenoprotein P is a useful biomarker of status in populations with relatively low selenium intakes because it responds to different dietary forms of selenium. To optimize the plasma selenoprotein P concentration in this study, 50 mu g Se/d was required in addition to the habitual intake of approximate to 55 mu g/d. In the context of established relations between plasma selenium and risk of cancer and mortality, and recognizing the important functions of selenoprotein P, these results provide important evidence for deriving estimated average requirements for selenium in adults. This trial was registered at clinicaltrials.gov as NCT00279812. Am J Clin Nutr 2010; 91: 923-31.