Manganese Exposure in Occupational Settings: Disruptions in Endothelial Function and Thyroid Regulation

TL;DR

Manganese exposure in workers is linked to lower thyroid hormones and altered endothelial function biomarkers, suggesting potential health risks.

Contribution

This study is the first to simultaneously examine thyroid and endothelial biomarkers in manganese-exposed workers.

Findings

Manganese-exposed workers had significantly higher blood manganese levels compared to controls.

Thyroid hormones (T3, T4, TSH) were lower in manganese-exposed workers.

Endothelial biomarkers ADMA and SDMA were elevated, while citrulline was reduced in exposed workers.

Abstract

Background: Manganese (Mn) exposure is common in welding and metal-processing occupations and has been implicated in both thyroid disruption and endothelial dysfunction through oxidative and nitric-oxide–related pathways. However, endocrine and vascular biomarkers have rarely been examined together in occupational settings. Methods: In this cross-sectional study, 95 Mn-exposed workers and 95 non-exposed controls were evaluated. Whole-blood Mn, triiodothyronine (T3), thyroxine (T4), thyroid-stimulating hormone (TSH), asymmetric dimethylarginine (ADMA), symmetric dimethylarginine (SDMA), arginine and citrulline were measured using validated Inductively Coupled Plasma—Mass Spectrometer and chemiluminescent immunoassays. Group differences were assessed using independent samples t-tests, and exposure–biomarker associations were evaluated using Pearson correlations (p < 0.05). Results: Mn-exposed workers had significantly higher blood Mn levels than controls (19.82 ± 4.54 vs. 10.22 ± 3.07 µg/L; p < 0.001). Thyroid hormones (T3, T4, and TSH) were significantly lower among Mn workers, representing a non-classical hormonal pattern, including T3 (2.47 ± 0.31 vs. 3.14 ± 0.42 ng/L; p < 0.001), T4 (1.02 ± 0.13 vs. 1.21 ± 0.18 ng/L; p < 0.001), and TSH (1.75 ± 0.53 vs. 2.88 ± 0.37 mIU/L; p < 0.001). Endothelial biomarkers also differed: ADMA (0.26 ± 0.14 vs. 0.19 ± 0.08 µmol/L; p < 0.001) and SDMA (0.24 ± 0.06 vs. 0.20 ± 0.03 µmol/L; p < 0.001) were higher, while citrulline was lower (18.77 ± 10.23 vs. 22.82 ± 6.70 µmol/L; p = 0.002). In Mn workers, blood Mn showed negative correlations with T3 (r = –0.535, p < 0.01), T4 (r = –0.331, p < 0.01), and TSH (r = –0.652, p < 0.01), and positive correlations with ADMA (r = 0.205, p < 0.05) and SDMA (r = 0.193, p < 0.05). Conclusions: These findings indicate measurable differences in thyroid hormones and dimethylarginine-related endothelial markers among Mn-exposed workers. While the cross-sectional design precludes causal inference, the combined pattern suggests a possible unusual biological response involving both endocrine regulation and nitric-oxide–related pathways. Further longitudinal studies incorporating oxidative stress markers, co-exposure assessment, and functional endothelial testing are needed to clarify the biological relevance of these associations.

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