Physiological Basis of Heat Adaptation in Indoor Factory Workers Exposed to Chronic Occupational Heat: A Mechanistic Study at Aba Industries, Abia State

Chronic occupational heat exposure in tropical manufacturing environments may induce progressive physiological heat adaptation, yet the cellular and systemic mechanisms of this adaptation process remain characterised predominantly in military and elite sports populations, with no Nigerian factory worker data available. This study investigated the physiological mechanisms of heat adaptation in chronically heat-exposed factory workers at Aba Industries, Abia State, South East Nigeria, making an original contribution to occupational physiology. A cross-sectional mechanistic design enrolled 80 workers with varying durations of heat exposure from six months to fifteen years, alongside 40 thermally unexposed administrative controls. Core temperature during a standardised heat stress challenge, onset of sweating threshold, sweat rate, plasma volume expansion markers including haematocrit shifts, heat shock protein 70 concentrations, and erythropoietin levels were assessed. Multivariate regression and dose-response analysis linked exposure duration to adaptation indices. Results showed that workers with longer heat exposure had earlier sweating onset, higher maximal sweat rates, lower exercise core temperature peaks, and significantly elevated plasma heat shock protein 70 concentrations compared to shorter-exposed and control participants. Plasma volume was expanded in long-duration workers relative to controls. Erythropoietin showed non-significant trends. Heat shock protein 70 was the strongest molecular indicator of adaptive status, increasing logarithmically with exposure years. This study provides the first characterisation of heat adaptation mechanisms in Nigerian industrial workers, advancing occupational thermal physiology. Heat acclimatisation standards for tropical factory settings are recommended. Keywords: heat adaptation, heat shock protein, occupational heat, sweating, Aba Industries.