Background Chronic Kidney Disease of unknown etiology is a growing health concern in low-and middle-income countries. While occupational heat stress is recognized as a potential contributor to kidney dysfunction among agricultural workers, the causal relationship between heat stress, core body temperature (Tc), and kidney function remains unclear.

Methods We conducted an observational study over two harvest seasons in Guatemala, following 148 male sugarcane workers across six months. Heat stress was measured using heat index (HI) and Tc with ingestible telemetric temperature pills. Particulate matter (PM) exposure was measured using personal breathing zone samplers worn during the work shift. We evaluated changes in kidney function using pre-and post-shift estimated glomerular filtration rate (eGFR). We applied G-computation to estimate causal effects and modeled hypothetical policy interventions reducing HI, Tc, and PM exposure, simulating occupational heat reduction strategies.

Results The average daily HI was 37.4 °C (SD: 2.0) with an average Tc increase of 1.16 °C (SD: 0.48) per shift. Both HI and Tc were associated with declines in eGFR across the work shift. At an HI of 34 °C, workers experienced an average eGFR decline of about 5 mL/min/1.73 m², while at 40 °C the decline exceeded 16 mL/min/1.73 m². High HI early in the season and elevated Tc later in the season contributed to kidney decline. A simulated intervention reducing HI exposure by 5% improved eGFR change by 1.46 mL/min/1.73 m². PM exposure did not have a significant impact on eGFR decline.

Conclusion Reducing workday heat exposure may mitigate acute kidney function decline. These findings support the development of policy interventions aimed at reducing external heat exposure and internal heat strain to protect kidney health. More research is needed to investigate the potential contribution of other environmental factors, including PM exposure.

The authors have declared no competing interest.

This work was funded with support from the National Institute of Environmental Health Sciences of the National Institutes of Health (NIEHS R01 ES31585-01A1). It was also supported by resources from Pantaleon under a memorandum of understanding with the University of Colorado. Funders had no role in data analysis, interpretation of data, writing the manuscript, or the decision to submit the findings for publication.

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The details of the IRB/oversight body that provided approval or exemption for the research described are given below:

This study was approved by the Colorado Multiple Institutional Review Board (COMIRB #20 0509) in the United States and ZUGUEME Comité de &Eacutetica Independiente in Guatemala.

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