A study of psoriasis and atopic dermatitis in relation to selenium

The object of the Thesis was to investigate the significance of the reduced whole blood, plasma and white cell selenium concentrations found in psoriasis and atopic dermatitis. A method of measuring the concentration of selenium in skin using hydride generation and atomic absorption spectroscopy was developed and validated. The method was precise and accurate and it was found that over 90% of added selenium could be recovered. The effect of supplementation with selenium alone or selenium and vitamin E was investigated in 69 subjects with psoriasis and 60 with atopic dermatitis in a double-blind study. Before supplementation started both sets of patients had reduced mean whole blood and plasma selenium concentrations but normal red cell glutathione peroxidase activity. The subjects were given 600 μg of selenium-enriched yeast alone, 600 μg of selenium enriched-yeast and 600 IU of vitamin E or placebo each day for 12 weeks. Neither supplementation regime reduced the severity of psoriasis or atopic dermatitis more than the placebo. 12 weeks supplementation produced a significant increase in the mean whole blood, plasma and platelet selenium concentrations, platelet glutathione peroxidase activity and plasma vitamin E concentration but not in the mean skin selenium concentration or red cell glutathione peroxidase activity. The rise in the white cell selenium concentration was equivocal. The absorption, excretion and Effective Volume of selenomethionine were determined in 10 subjects with psoriasis, 9 with atopic dermatitis and 10 controls by measuring the whole body and plasma retention of intravenous and oral doses of 75Se-1-selenomethionine. No significant differences were found between the three groups. The reduced plasma selenium concentrations found in psoriasis and atopic dermatitis were not caused by a decreased absorption, an increased excretion or an altered distribution of selenomethionine. Selenium supplementation increased the whole blood and plasma selenium concentrations but did not reduce the severity of psoriasis or atopic dermatitis, possibly because the concentration of selenium in the skin did not increase.