Heat and Health: Using physiological evidence to build resilience to a warming planet

Abstract:

Extreme heat can have a devastating impact on human health and wellbeing across the human lifespan. During pregnancy, excess heat exposure leads to a 45% increase in the risk of stillbirths. Occupational heat stress from early adulthood through to retirement costs the Australian economy alone >$6B per year in lost productivity. Heat extremes (heatwaves) cause more deaths than all other natural disasters combined, with >80% of cases occurring in those aged >75 y. In many tropical countries, the secondary impacts of heat stress on human health are also observed, with hot temperatures the leading barrier to overnight mosquito-net use, and thus a major factor aggravating risk of diseases such as dengue and malaria. Simultaneously, our planet is heating up. Heatwaves have doubled globally since 1990, and temperatures currently classified as “extreme” will be the new “normal” by 2030. For society to not only survive, but thrive, in an inevitably warmer future, we must urgently build resilience to heat across all stages of life.

Physiologists can make significant contributions. Through a variety of experimental approaches, they can first help understand the underlying mechanisms responsible for elevated heat-related mortality/morbidity risk in specific sub-populations. Indeed, in many cases (e.g. those with cardiovascular disease or renal disease) high body temperatures per se may not be the primary culprit. Rather, the autonomic mechanisms engaged to defend dangerous rises in body temperature may elicit different types of physiological strain that are intolerable due to other disease-related infirmities. Using this information, optimal protective solutions can then be developed, and their efficacy for reducing physiological heat strain systematically assessed, in physiological studies utilising human participants in climate-controlled chambers that simulate a range of historical and future heatwaves. These experimental findings alone are not sufficient though and collaboration with public health authorities, and the wider scientific community is needed to ensure that this information is optimally translated into evidence-based public health advice.