Thyroid homeostasis and retinol circulating complex relationships in a severe iodine-deficient area of Senegal

In adult subjects living in a severely iodine-deficient area (median urinary iodine 10 microgram/L), we evaluated the biochemical parameters of protein malnutrition in relation to thyroid homeostasis. Serum transthyretine (TTR), retinol binding protein (RBP) and retinol, all components of the retinol circulating complex (RCC), as well as ceruloplasmin levels, were determined in 63 subjects (44 F/19 M). These comprised 21 controls, 31 who were euthyroid with goiter WHO stage 2 or 3 and 11 who met the criteria of hypothyroidism (i.e. FT4 < 8 pmol/L and TSH > 4.13 mU/L) with goiter stage no more than 1b. No differences in the values of TTR and RBP were found between males and females, whereas the retinol values were slightly higher in males. The mean retinol binding protein values were lower than the normal range in all three groups but were significantly lower (p < 0.01; < 0.05) in hypothyroid subjects than in the other two groups. All hypothyroid subjects exhibited reduced retinol binding protein levels and 1/3 of them showed a marked decrease. The circulating levels of transthyretine were also lower than the normal range for western countries. 45% of the hypothyroid, 26% of goitrous and 9% of control subjects exhibited a transthyretine lower than 12 mg/dl, but the mean values were not dissimilar. The mean retinol values were within the normal range in all three groups but were lower in hypothyroid as compared to the controls (< 0.01). The resulting retinol/RBP ratio was over 1 in both the whole sample and in the subgroups. Ceruloplasmin levels were in the normal range in all groups. The data indicated that hypothyroid subjects had reduced retinol binding protein and retinol circulating complex network compared to euthyroid subjects.