Selenium, zinc, and thyroid hormones in healthy subjects

Abstract

Iodothyronine 5' deiodinase, which is mainly responsible for peripheral T3 production, has recently been demonstrated to be a selenium (Se)-containing enzyme. The structure of nuclear thyroid hormone receptors contains Zinc (Zn) ions, crucial for the functional properties of the protein. In the elderly, reduced peripheral conversion of T4 to T3 with a lower T3/T4 ratio and overt hypothyroidism are frequently observed. We measured serum Se and RBC GSH-Px (as indices of Se status), circulating and RBC Zinc (as indices of Zn status), thyroid hormones and TSH in 109 healthy euthyroid subjects (52 women, 57 men), carefully selected to avoid abnormally low thyroid hormone levels induced by acute or chronic diseases or calorie restriction. The subjects were subdivided into three age groups. To avoid under- or malnutrition conditions, dietary records were obtained for a sample of 24 subjects, randomly selected and representative of the whole population for age and sex. Low T3/T4 ratios and reduced Se and RBC GSH-Px activity were observed only in the older group. A highly significant linear correlation between the T3/T4 ratio and indices of Se status was observed in the older group of subjects (r = 0.54; p < 0.002, for Se; r = 0.50; p < 0.002, for RBC GSH-Px). Indices of Zn status did not correlate with thyroid hormones, but RBC Zn was decreased in older as compared with younger subjects. We concluded that reduced peripheral T4 conversion is related to impaired Se status in the elderly.

Selenium Status Is Positively Associated with Bone Mineral Density in Healthy Aging European Men

“…Although an altered metabolism of TH due to low Se status has been proposed as a mechanism for the age-dependent changes in TFTs [ 7 , 8 ], extensive profiling of thyroid parameters in the current study did not reveal any association of TFTs with Se status. Our analysis included assessment of T3/T4 and T3/rT3 ratios as a reflection of the peripheral metabolism of TH.…”

“…Peripheral metabolism of TH levels is predominantly mediated by the selenoenzymes type 1, type 2, and type 3 deiodinase (D1-3), which all contain a selenocysteine in their catalytic centre. An altered metabolism of TH due to low Se status has been proposed as a mechanism for the age-dependent changes in thyroid parameters [ 1 , 7 – 13 ].…”

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

“…The mean plasma selenium concentration of our elderly participants (1.20 lmol/L) was higher than in an earlier cohort of older New Zealand women (0.90 lmol/L) (14), a 1977 study of older adults (0.48 lmol/L) (34), and New Zealand adults (1.14 lmol/L) (10). We had expected the selenium status of our older adults to be lower than that of younger adults, as shown in several studies (27,34,35), a likely result of low micronutrient intake in older adults (36,37). The higher than expected selenium status of our older participants reflects the trend of increasing selenium status among New Zealand residents (8,38).…”

The effect of selenium on thyroid status in a population with marginal selenium and iodine status

“…Kvícala et al (1995) reported significant relationships over a range of measures of Se status and thyroid hormone parameters (T 4 and T 3 :T 4 ) in 380 Czech inhabitants aged 6-65 years, but not always in all of the narrower age ranges. Olivieri et al (1996) reported a highly significant positive correlation between the T 3 :T 4 ratio and indices of Se status in healthy elderly Italian subjects with marginal Se status, concluding that reduced peripheral conversion of T 4 is related to inadequate Se status in the elderly. Se supplementation resulted in a reduction of T 4 but no changes in the T 3 :T 4 ratio (Olivieri et al 1995).…”

“…Although our blood Se concentrations may not be in the range in which effects on thyroid function have been observed, the combination of low Se status and mild I deficiency may be significant. A number of human studies have shown alterations in the T 3 :T 4 ratio associated with low Se and I status (Kvícala et al 1995;Olivieri et al 1996;Ravaglia et al 2000). Therefore, it is important to determine whether there are any detrimental effects of marginal status of Se and I in our population.…”