Heat stress and neurological biomarkers in outdoor workers: a cross-sectional observational study

Climate change has increased heat exposure, especially for outdoor workers, raising concerns about neurological damage. This study examined the relationship between occupational heat stress and serum biomarkers of CNS injury-serum neurofilament light chain (sNfL), serum glial fibrillary acidic protein (sGFAP), and serum concentrations of growth differentiation factor-15 (sGDF-15)-to assess subclinical neurophysiological effects in workers operating in high-temperature environments.

We conducted a cross-sectional observational study between June and October 2023 in Apulia, southeastern Italy. Thirty-seven outdoor workers employed in agricultural and construction sector were recruited. Blood samples were collected twice per week (beginning and end of workweek) to measure sNfL, sGFAP, and sGDF-15 levels. Heat exposure was monitored using the Wet Bulb Globe Temperature (WBGT) index. Multiple linear regression models were used to assess associations between biomarker levels and heat exposure, adjusting for demographic and occupational factors.

A significant increase in sNfL was observed at the end of the workweek (median: 10.3 pg/mL at T1 vs 12.2 pg/mL at T2; p = 0.045). Multiple regression analysis showed that sNfL was negatively associated with BMI (β = -0.071, p = 0.010) and positively with weekly WBGT (β = 0.087, p = 0.022). For sGDF-15, WBGT was the only significant predictor (β = 0.092, p = 0.002), while the model for sGFAP was not statistically significant (p = 0.147).

Our findings provide evidence of a direct association between occupational heat stress and biomarkers indicative of CNS injury among outdoor workers, underscoring the need for targeted interventions to reduce heat exposure and monitor neurological health in vulnerable populations.