Association between work in deforested, compared to forested, areas and human heat strain: an experimental study in a rural tropical environment

Abstract

Background.With climate change, adverse human health effects caused by heat exposure are of increasing public health concern. Forests provide beneficial ecosystemservices for human health, including local cooling. Fewstudies have assessed the relationship between deforestation and heatrelated health effects in tropical, rural populations.We sought to determinewhether deforested compared to forested landscapes are associatedwith increased physiological heat strain in a rural, tropical environment.Methods.We analyzed data from363 healthy adult participants fromten villages who participated in a two-by-two factorial, randomized study in EastKalimantan, Indonesia from 10/1/17 to 11/6/17.Using simple randomization, field staff allocated participants equally to different conditions to conduct a 90min outdoor activity, representative of typicalwork.Core body temperature (CBT) was estimated at each minute during the activity using a validated algorithmfrombaseline oral temperatures and sequential heart rate data,measured using chest bandmonitors.We used linear regressionmodels, clustered by village and with a sandwich variance estimator, to assess the association between deforested versus forested conditions and the number ofminutes each participant spent above an estimatedCBT threshold of 38.5 °C. Results. Compared to those in the forested condition (n=172), participants in the deforested condition (n=159) spent an average of 3.08 (95%confidence interval (CI) 0.57, 5.60) additionalminuteswith an estimatedCBT exceeding 38.5 °C, after adjustment for age, sex, bodymass index, and experiment start time,with a larger differenceamong thosewho began the experiment after 12noon (5.17 [95%CI 2.20, 8.15]).Conclusions. In this experimental study in a tropical, rural setting, activity in a deforested versus a forested setting was associatedwith increased objectively measured heat strain. Longer durations of hyperthermia can increase the risk of serious health outcomes. Land use decisions should consider the implications of deforestation on local heat exposure and health as well as on forest services, including carbon storage functions that impact climate changemitigation.