Selenium is a trace mineral that is incorporated into selenoproteins, the most well known of which is the antioxidant enzyme glutathione peroxidase. However, selenoprotein P is increasingly being seen as a reliable marker for selenium status. Deficiency of selenium is associated with increased mortality from cancer, and research has shown that supplementation with 200 µg of selenium per day in the form of selenium yeast is able to reduce the overall mortality and morbidity of cancer by 50 %1. Research in China suggests an inverse association between selenium intake and subsequent deaths from both esophageal squamous cell carcinoma and gastric cardia cancer (here). Because selenium is an essential trace mineral, it must be supplied by the diet. Evidence suggest that selenium intakes are below the recommended levels in many Western populations, and declining. The current mean intake of selenium is 48 to 58 µg per day in the United Kingdom.
Research conducted in the American Journal of Clinical Nutrition in 20102 attempted to investigate the intakes of selenium necessary to increase platelet glutathione peroxidase activity, plasma selenium and selenoprotein P levels to optimal levels. Researchers fed 119 healthy men and women aged 50 to 64 years a 50, 100 or 200 µg selenium yeast supplement (containing ~ 60 % selenomethionine), a selenium enriched onion meal (~ 66 % γ-glutamyl-methylselenocysteine, providing 50 µg selenium a day), an unenriched onion meal or a placebo for 12 weeks. The results showed that baseline plasma selenium concentration increased from 95.7 ng/mL to 118.3, 152.0 and 177.4 ng/mL in subjects who consumed 50, 100 and 200 µg selenium yeast, respectively. Selenoprotein P levels increased from 4.99 µg/mL to 6.17, 6.73, 6.59 and 5.72 µg/mL in subjects who consumed 50, 100 and 200 µg selenium yeast, and the enriched onion meal, respectively. Glutathione peroxidase activity was not affected by any of the selenium treatments.
This research supports previous findings regarding the ability of supplements to raise levels of selenoprotein P and plasma selenium, although glutathione peroxidase activity in platelets did not respond to supplements. Selenium yeast at the 50 µg dose increased selenoprotein P levels at a faster rate that the selenium from enriched onions (~50 µg selenium), but after 10 weeks there was no difference in selenoprotein levels between the two groups. Selenoprotein P levels reached a plateau with both the 50 µg selenium yeast and the selenium enriched meals, and no further rise in selenoprotein P was seen with the 100 or 200 µg dose. This suggests that in addition to the ~ 48 to 55 µg intake of selenium from food, 50 µg of selenium from an organic source (selenomethionine or γ-glutamyl-methylselenocysteine) is enough to optimise seleoprotein P levels.
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