Thyroid-stimulating hormone and thyroid hormone levels in association with occupational hazards in male coal miners

Background Thyroid hormones are crucial for development and proper functioning of human physiological systems. Current research on the thyroid mainly focuses on the impacts of lifestyle factors on thyroid dysfunction, while less attention is paid to the factors affecting thyroid hormone levels, especially occupational hazards, which warrants further investigation.

Objective To investigate the associations between occupational hazard exposure and thyroid-stimulating hormone (TSH) and thyroid hormone levels in male coal mine workers.

Methods A cross-sectional study design was adopted. A total of 12564 workers who participated in the occupational health check-ups at the Xishan Coal Electricity (Group) Corporation Occupational Disease Prevention and Control Institute in 2023 and met the inclusion and exclusion criteria were selected as research subjects. A self-designed electronic questionnaire was used to collect basic information, occupational history, and lifestyle habits of all study subjects. Height, weight, thyroid function test results, and occupational hazard exposure of the study subjects were obtained through occupational health examinations and routine workplace occupational hazard detection records. Generalized linear regression was used to analyze the associations between occupational hazard exposure and the levels of TSH and thyroid hormones.

Results The median (P₂₅, P₇₅) levels of triiodothyronine (T3), thyroxine (T4), free triiodothyronine (FT3), free thyroxine (FT4), and TSH in the included 12564 male coal mine workers were 1.16 (1.03, 1.29) ng·mL⁻¹, 7.70 (6.70, 8.90) μg·dL⁻¹, 3.63 (3.40, 3.84) pg·mL⁻¹, 1.19 (1.08, 1.30) ng·dL⁻¹, and 1.93 (1.36, 2.78) μIU·mL⁻¹, respectively. The overall abnormality rate of thyroid hormones was 2.83%, with the highest rate for subclinical hypothyroidism (1.83%), followed by hyperthyroidism (0.37%), hypothyroidism (0.32%), and subclinical hyperthyroidism (0.31%). After adjustment for confounding factors, the generalized linear regression model showed that long working hours were associated with higher levels of T3 and FT3, with β (95%CI) values of 0.011 (0.003, 0.019) and 0.038 (0.019, 0.057) respectively. Night shift work was linked to increased TSH levels and decreased FT4 levels, with β (95%CI) values of 0.171 (0.016, 0.326) and −0.012 (−0.019, −0.006) respectively. Coal dust exposure was associated with decreased levels of T3 and T4, with β (95%CI) values of −0.022 (−0.037, −0.008) and −0.320 (−0.434, −0.207) respectively. Noise exposure was related to decreased levels of T4 and FT4, with β (95%CI) values of −0.102 (−0.166, −0.038) and −0.020 (−0.027, −0.013) respectively.

Conclusion The TSH and thyroid hormone levels of coal miners are mostly within the normal reference ranges, with a low abnormality rate. Long work hours, night shift work, coal dust, and noise are associated with the levels of TSH and thyroid hormone levels in the male miners. Coal companies should reasonably arrange working hours, optimize the night shift scheduling system, and enhance protection against coal dust and noise to promote occupational health and safeguard the physical health of miners.