Thyroid function during prolonged exposure to fluorides

Abstract

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.

Fluoride Exposure Induces Inhibition of Sodium/Iodide Symporter (NIS) Contributing to Impaired Iodine Absorption and Iodine Deficiency: Molecular Mechanisms of Inhibition and Implications for Public Health

“…Further studies conducted in China, also found that excessive F exposure inhibited thyroid iodine uptake in children [10]. Similar effects were observed in a Russian study examining the effects of occupation exposure to F among subjects with signs of chronic fluorosis [18]. Consistent with these findings, a recent all Ireland study which measured iodine status in adolescent girls throughout the island of Ireland; which includes the Republic of Ireland (RoI) and Northern Ireland (NI), found that median UIC’s were significantly lower in adolescent girls in all participating locations in the RoI compared to NI.…”

“…As previously elucidated, Tg has been found to play a crucial role in downregulating NIS expression. There is robust evidence from epidemiological studies conducted in different geographic regions to show that F exposure increases TSH levels in humans [12,15,18,29,35,165,166,167,168,169,170,171,172,173,174,175,176,177,178]. Since TSH stimulates thyroid follicular cells to produce Tg [179,180]; serum Tg concentrations are typically higher in individuals with a raised TSH or primary hypothyroidism [181].…”

Fluorosis and Iodine Deficiency Disorders in India

“…An analysis of immune status showed that T-lymphocyte count enhanced, but the cells were nonfunctional due to reduced FT 3 levels 21 . In yet another Russian report, amongst industrial workers exposed to Fand suffering from industrial fluorosis, aberration in the thyroid gland function was reported 22 .…”

“…The second objective of the present review is to highlight the implications of diseases caused by excess fluoride and iodine deficiency and the synergy of these two elements in a biological system. There are nine studies from India [7][8][9][10][11][12][13][14][15] and another eight studies from other nations [16][17][18][19][20][21][22][23] reported on goitre prevalence in populations with iodine sufficiency, goitre in fluoride endemic areas and goitre in industrial workers exposed to fluorine fumes and dust. These studies have been described in the section dealing with human studies.…”

Evaluation of the Effects of Fluoride and Associated With Lead in Animal Model and Physical-Chemical Analysis of Public Supply Water and of the Sinos River in the South of Brazil

“…In Delhi, India, from a group of 90 children with dental fluorosis living in areas with endemic fluoride, not iodine deficient, 54.4% had well-defined hormonal disorders (Susheela et al 2005). Other studies in China and Russia corroborate the relation fluoride/hypothyroidism with changes in thyroid hormones, including reduced T3 and increased TSH, in populations exposed to high levels of fluoride in the workplace or in water (Bachinskii et al 1985;Mikhailets et al 1996). Zhao et al (1998)…”