Effect of Selenium Supplementation on Thyroid Hormone Metabolism in an Iodine and Selenium Deficient Population

Objective: Severe selenium deficiency has been documented in northern Zaïre, already known as one of the most iodine deficient regions in the world and characterized by a predominance of the myxoedematous form of cretinism. This has been attributed to the double deficiency of essential trace elements. A short selenium supplementation programme was conducted in this area to evaluate the effects of a selenium supplementation on thyroid diseases.

Design: Placebo or selenium 50 micrograms as selenomethionine was administered once daily for 2 months. Blood and urine samples were collected before and after supplementation.

Patients: Fifty-two healthy schoolchildren from northern Zaire.

Measurement: Selenium status, thyroid function and urinary iodide were determined.

Results: After 2 months of selenium supplementation, mean +/- SD serum T4 decreased from 73.1 +/- 45.4 to 48.3 +/- 23.7 nmol/l (P less than 0.001), serum FT4 from 11.8 +/- 6.7 to 8.4 +/- 4.1 pmol/l (P less than 0.01), and serum rT3 from 124 +/- 115 to 90 +/- 72 pmol/l (P less than 0.05), without significant change in serum T3 and serum TSH.

Conclusion: Deiodinase type I which has been shown to be a seleno-enzyme could account for the changes in thyroid hormones in our subjects. Our data show that selenium plays a definite role in thyroid hormone metabolism in humans. Selenium could be an important cofactor in the clinical picture of iodine deficiency in Central Africa and could be involved in the aetiology of both forms of cretinism.