Effects of heat stress on human health : input into health impact assessment of climate change

Abstract

Global warming has led to renewed interest in the occurrence of heat stress in the population along with its determinants and consequences. Heat stress can create unsafe working conditions and affect the health of workers. Heat waves are also unsafe and in 2003 led to many avoidable deaths in Europe. Most heat stress research has been conducted in high-income countries in temperate latitudes. This leaves knowledge gaps regarding heat stress and its effects for tropical settings. Thailand is a tropical developing country where average temperatures have increased over the last 50 years and further increase is expected. Heat stress has been shown to be a serious problem in a variety of Thai workplaces. But several important public health questions remain and they are the focus of this thesis. The questions are as follows: are there any health impacts of heat stress i) on Thai workers? ii) on the overall population in Thailand? iii) expected for the Thai population in future due to the projected increase of temperature? To answer these research questions, five studies were carried out. They investigate the occurrence of heat stress and its association with various health outcomes, including death. The first four studies use heat exposure and morbidity data from a large national Thai Cohort Study (TCS) covering the period 2005 to 2009. The fifth study uses national weather and mortality data covering 1999 to 2008. The first study explores the relationship between self-reported heat stress and psychological distress and overall health status of Thai workers using TCS data. There was a strong association between heat stress and worse mental health outcomes among workers. The second study uses TCS data on heat stress and occupational injury among Thai workers. The evidence connects heat stress and occupational injury and also identifies several factors that increase heat exposure (male sex, rural residence, physical job). The third study relates heat stress and incident kidney disease amongst Thai workers using longitudinal TCS data that documented prolonged heat exposure. Heat stress was a significant risk factor for kidney disease among male workers, especially physical workers age 35 years or more. The fourth study shows that health and wellbeing decreased (low energy, emotional problems, and low life satisfaction) as more heat stress interfered with daily activities (sleeping, daily travel, work, housework and exercise). So heat stress has an adverse health impact on the overall population. The final study shows that Thai mortality from 1999 to 2008, adjusted for weather and air pollution, varied by air temperature. A U-shaped association between monthly maximum temperature and mortality was found for each season (hot, wet, and cold), and each region (North, Northeast, South, and Centre). The 4 degrees Celsius increase in temperature from climate change, as expected by 2100, could increase annual heat-related deaths by 32,000 as well as increasing other impacts on health and well-being. The health impact information in this thesis points to the need to improve health surveillance and public awareness regarding risks of heat stress in Thailand.