Factors affecting thyroid nodule among coal miners: a prospective nested case-control study in Xinjiang, China

Thyroid health issues have long been a critical focus in public health research and policy discussions. However, little is known about the thyroid health in coal miners. This study aimed to identify risk factors for thyroid nodules in coal miners.

This study employed a nested case-control design. A total of 697 male coal miners with no abnormalities detected on thyroid ultrasound at baseline (2019) were enrolled as the study population. Baseline data collection included demographic characteristics, health indicators, and occupational coal-dust exposure concentrations. Follow-up continued until December 2024. Based on the final thyroid ultrasound results at the end of follow-up, workers who developed new-onset thyroid nodules were assigned to the case group, while those whose ultrasound results remained normal throughout the follow-up period were assigned to the control group.

The incidence of thyroid nodules in the study subjects was 18.65%. Cox proportional hazards model showed that the risk of thyroid nodules in the high-dose coal dust exposure group was 2.41 times higher than that of the blank control group (HR = 2.41, 95% CI:1.473-3.936), abnormal urine analysis was 1.77 times higher than the normal group (HR = 1.77, 95% CI: 1.152-2.713), abnormal high-density lipoprotein cholesterol was 1.60 times higher than the normal group (HR = 1.60, 95% CI: 1.072-2.394), and abnormal fasting blood glucose was 1.62 times higher than the normal group (HR = 1.62, 95% CI: 1.071-2.454). All of these factors were identified as independent risk factors for thyroid nodules. Compared with workers with 0-5 years of exposure, the risk of thyroid nodules was 0.31 times lower in those with 5-10 years of exposure and 0.49 times lower than those with 25-30 years of exposure. A restricted cubic spline model further validated that, after adjusting for exposure duration, the risk of thyroid nodules increased with age after 45 (overall trend p = 0.0134), and this association was linear (nonlinearity test p = 0.0575).

High-dose exposure to coal dust, abnormal urine routine results, abnormal high-density lipoprotein cholesterol, abnormal fasting blood glucose, and age >45 years were identified as significant risk factors for thyroid nodules in coal miners.