Occupational heavy metal exposure and endocrine–metabolic biomarkers: a retrospective analysis of 34,595 screened individuals in Türkiye

Background Heavy metals and trace elements can act as endocrine-disrupting chemicals and have been linked to thyroid, glucose, lipid, and hepatic abnormalities. We aimed to explore associations between routinely measured metal concentrations and biochemical/endocrinological parameters in a large occupational screening dataset from Türkiye. Methods Periodic examination records from 37,763 individuals evaluated at a national occupational and environmental diseases hospital/toxicology laboratory between November 2021 and October 2023 were retrospectively reviewed; after prespecified exclusions, 34,595 participants were included. Metal measurements were performed in whole blood, serum, and urine samples as requested in routine surveillance; for each analyte, results were categorized as within or above the interpretive limit used by the laboratory information system. Primary comparisons focused on arsenic, cadmium, lead, manganese, and zinc because of occupational relevance and sample size. Routine biochemistry, lipid profile, and thyroid function tests were extracted when available, and FIB‑4 and estimated glomerular filtration rate (eGFR, CKD‑EPI) were calculated. Results Among participants with thyroid function tests (n = 9,956), thyroid dysfunction was observed in 14.3% (subclinical hypothyroidism 11.9%). Among those with fasting glucose and/or HbA1c (n = 20,738), diabetes mellitus and prediabetes were present in 12.8% and 10.0%, respectively. In univariable comparisons, several metals above the interpretive limit were associated with differences in metabolic biomarkers, including lower HDL with elevated cadmium, lower HDL/LDL with elevated manganese, and higher ALT/AST and triglycerides with elevated zinc. Participants with elevated levels of cadmium, lead, and manganese tended to be younger, and elevated levels of arsenic, cadmium, and zinc were more frequent in males. After within-metal false discovery rate adjustment, the most robust signals were observed for lead- and zinc-associated differences, while other associations should be interpreted as exploratory. Conclusion Thyroid dysfunction and dysglycemia were common among the tested participants, and elevations in specific metals were associated with lipid and liver enzyme patterns. These findings support strengthening exposure-reduction measures and targeted clinical monitoring in high-risk occupational groups.