Impact Assessment of Heat Stress on Population Health in Japan and China

In accordance with the rapid increase in greenhouse gas emissions, climate models predict an increase in the global surface temperature in the future. With regard to human health, it is thought that global warming may have a critical impact due to increased heat stress in summer. Furthermore, enormous population growth is accelerating the heat island phenomenon in urban areas. Since global warming and the heat island phenomenon will increase heat stress in summer in communities, this paper examines population health risks caused by heat stress. An epidemiological survey showed the incidence of heat-related illness to be significantly correlated to high temperatures in Japan and China. The incidence of heat-related illness in populations especially among the elderly increased exponentially with rising maximum daily temperatures in summer. The incidence of heat-related illness increased in the daytime when the maximum daily temperature and the heat index temperature in summer rose above the threshold temperature. The incidence of pneumonia was correlated with cold temperatures in winter and hot temperatures in summer. Therefore, it is necessary to study age- and gender-dependent health damage of populations in local communities under extreme heat stress in hot environments. To evaluate the age-related response of populations against health damage from hot temperatures, we studied the biomedical response of animals to heat stress. Conditions of hyperthermia caused by exposure to hot environments resulted in marked damage to some essential organs in animals. Damage from heat-stress-inducible oxygen free radicals becomes more severe in aged animals. Since aging and hyperthermia have a synergistic effect on peroxidative damage, it is essential to have protective enzyme activities against oxygen free radicals. To prevent health impacts from heat stress in populations due to global warming and the heat island phenomenon, it will be necessary to improve environment design in urban and rural areas and to promote population health in aged persons in the world.