Thyroid function during prolonged exposure to fluorides

Thyroid function was examined in 165 workers of electrolysis shops of aluminum production with more or less expressed signs of chronic fluoride intoxication (fluorosis) by radioimmunoassay of hormones and the test of 13II absorption by the thyroid. The detected thyroid abnormalities were characterized by a moderate reduction of iodine-absorbing function of the thyroid, low T3 with normal T4 level, and a slight increase of TTH concentration. These changes augmented with longer service and fluorosis progress. Hence, the syndrome of low T3 and reduced absorption of 1311 may be considered as diagnostic signs of fluorosis. In case of toxic involvement of the liver in fluorosis patients, low T3 syndrome is observed much more frequently: in 75.6% cases. Liver abnormalities evidently lead to disorders in the peripheral conversion of T4 in T3, occurring primarily in liver parenchyma. Indirect effect of fluorine on the enzymatic system of deiodination cannot be ruled out as well.