Serum levels of thyroxine, thyroid-stimulating hormone, and anti-thyroid peroxidase antibodies and their association with anxiety in environmentally exposed populations in Kazakhstan

Little is known about the impact of environmental pollution on thyroid function in the non-occupationally exposed population of Kazakhstan. This study aimed to investigate serum levels of thyroxine (T4), thyroid-stimulating hormone (TSH), and anti-thyroid peroxidase (TPO) antibodies in the environmentally exposed population of Kazakhstan in relation to symptoms of anxiety. A total of 1,388 nominally healthy individuals residing in areas exposed to three major types of environmental pollution prevalent in Kazakhstan—non-ferrous metallurgy, condensate gas extraction, and activities of the Semipalatinsk Nuclear Test Site (SNTS)—were enrolled. All comparisons were made with 493 individuals residing in settlements without industrial or military pollution. Serum-free T4, TSH, and anti-TPO levels were tested using a solid-phase chemiluminescent immunoassay. The Generalized Anxiety Disorder 7-item (GAD-7) inventory was utilized to screen for anxiety symptoms. The prevalence of subclinical hypothyroidism was significantly higher in residents of settlements near the condensate gas field than in control sites (20.3 vs. 15.0%). In comparison, the prevalence of overt hypothyroidism was insignificantly higher (0.7 vs. 0.6%). The prevalence of subclinical hyperthyroidism was insignificantly higher in residents of settlements around the SNTS. The prevalence of overt hyperthyroidism was insignificantly higher in residents of areas proximal to the condensate gas field compared to the controls. The prevalence of both normal and elevated serum levels of anti-TPO antibodies did not differ significantly between different sites. Moderate and severe anxiety symptoms were the least common in residents of the two control sites (5.9%). This study carries potential implications for tailored public health interventions and policies.