The Impact of Heat Stress Exposure on Heat-Related Symptoms, Physiological Parameter Responses, and Productivity Among Sugarcane Workers in Thailand

Abstract

Introduction: Global warming raises concern over the impact of elevated temperatures on agricultural workers, particularly in tropical countries like Thailand. This study assessed the effects of heat stress exposure on heat-related symptoms, physiological parameter responses, and productivity among Thai sugarcane workers. Methods: A total of 300 sugarcane workers from Nakhon Sawan Province, Thailand, participated in the study during the cooler and hotter harvesting periods of 2023. Data were collected during the cool season (14 non-consecutive d, from Jan 18 to Feb 10) and the hot season (11 d, from Mar 11 to Mar 20). Heat stress exposure was assessed using Wet-Bulb Globe Temperature (WBGT) measurements, recorded over entire work shifts in the sugarcane fields on all data collection days. A full work shift time-weighted average effective WBGT (WBGTeff-FS-TWA), adjusted for clothing factors, was calculated to provide an estimate of heat stress exposure. Heart rate, blood pressure, and body temperature were recorded pre- and post-shift. Number of sugarcanes cut per hour were determined by observation. Statistical analyses examined associations between WBGTeff-FS-TWA and health or productivity outcomes, adjusting for confounders. Results: The mean WBGTeff-FS-TWA was 31.3 ± 2.8 °C, with a range of 22.9 – 35.4 °C. The sugarcane harvesters’ heat stress exposure in both seasons exceeded the American Conference of Governmental Industrial Hygienists (ACGIH) - Threshold Limit Value (TLV) for 72.7% of the working time in the cooler months and 90.9% in the hotter month. For a 1°C increase in WBGTeff-FS-TWA, the adjusted relative risk for the number of heat-related symptoms was 1.10 (95% CI: 1.08, 1.13). WBGTeff-FS-TWA was not significantly associated with either post-shift systolic or diastolic blood pressure but was with post-shift results of both heart rate (β (95% CI): 0.61 (0.24, 0.98)) and body temperature (0.02 (0.002, 0.03)), adjusting for pre-shift results and confounders. An increase in WBGTeff-FS-TWA significantly reduced the number of sugarcane stalks harvested per hour (-8.59 (-16.19, -0.99)), adjusting for confounders. Conclusion: The findings highlight heat-induced health issues and productivity loss. As global temperatures rise, this study underscores the growing impact of heat stress exposure on agricultural populations. Interventions to reduce heat stress levels are urgently needed. Heat stress in agricultural and other outdoor work in a tropical climate is a serious problem.

Date of Award	12 Nov 2025
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Martie Van Tongeren (Main Supervisor), Holly Shiels (Co Supervisor), Matthew Gittins (Co Supervisor) & Andrew Povey (Co Supervisor)