Thyroid function parameters during a selenium repletion/depletion study in phenylketonuric subjects

Abstract

Phenylketonuric (PKU) subjects have a limited supply of selenium (Se) in their phenylalanine-restricted diet. A Se repletion (1 microgram Se/kg/day)/depletion study was conducted in PKU children to determine the effect of Se on thyroid function parameters. The initial plasma Se concentration (mean +/- SD: 0.26 +/- 0.12 mumol/L, p < 0.00003, n = 10) and glutathione peroxidase (GSH-Px) activity (140 +/- 58 U/L, p < 0.00003, n = 10) were significantly lower compared to age-matched controls. After 14 weeks of supplementation, the plasma Se concentration (mean +/- SD: 0.74 +/- 0.20 mumol/L) normalized (normal range: 0.57-1.15 mumol/L, mean +/- SD: 0.76 +/- 0.13 mumol/L, n = 32) and remained stable thereafter during repletion. Plasma GSH-Px activity reached normal values after 18 weeks of supplementation (312 +/- 57 U/L; normal range: 238-492 U/L, mean +/- SD: 345 +/- 54 U/L, n = 32) and increased significantly for up to eight weeks thereafter (332 +/- 52 U/L). Individual and mean thyroid parameters were initially normal in all cases. The mean concentrations of plasma thyroxine (T4: p < 0.025), free T4 (FT4: p < 0.01) and reverse triiodothyronine (rT3: p < 0.005) decreased to 75% of their initial value within three weeks of Se supplementation and remained stable thereafter, within a normal physiological range during selenium supplementation. They increased back to their initial values three weeks (T4: p < 0.05, FT4: p < 0.05) and six weeks (rT3: p < 0.025) respectively, after the end of the supplementation. In conclusion, Se supplementation modifies thyroid function parameters in Se-deficient PKU subjects most likely by an increase in activity of type I 5'-deiodinase (5'-DIase I).

Kashin–Beck Osteoarthropathy in Rural Tibet in Relation to Selenium and Iodine Status

“…In a study of Belgian children, the threshold for optimal serum glutathione peroxidase activity was a serum selenium concentration of 55 ng per milliliter (696 nmol per liter). 26 In other studies, the serum selenium concentrations that corresponded to optimal glutathione peroxidase activity measured in platelets were 95 to 135 ng per milliliter (1207 to 1715 nmol per liter). 27 Iodothyronine deiodinases are selenoproteins involved in the deiodination of thyroid hormones.…”

Selenium and iodine supplementation: effect on thyroid function of older New Zealanders

“…Our trial differed from earlier studies in that mean plasma selenium concentration at baseline (1.20 lmol/L) was higher, as was that of elderly British subjects (1.16 lmol/L) (16) and US subjects (1.78 lmol/L) (17), compared with 0.83 lmol/L (9) and 0.81 lmol/L (29) in the 2 earlier trials. In studies of children severely deficient in selenium and iodine (30) or phenylketonuria (31), when selenium supplementation decreased T 4 concentration, baseline plasma selenium was very low (34 and 0.26 lmol/L, respectively).…”

Role of Iodine, Selenium and Other Micronutrients in Thyroid Function and Disorders

“…Disturbed serum Se status and altered thyroid hormone serum levels are also found in patients on protein-poor diets (e.g., phenylketonuria), on long-term total parenteral nutrition (TPN), or suffering from cystic fibrosis or Crohn's disease or people who have had a large portion of the small intestine surgically removed, and in animal models, e.g., during lactation or intoxication by heavy metals (mercury, cadmium) [235,[238][239][240][241][242]. TPN solutions and specialized diets are now supplemented with selenium to prevent such problems [118].…”