Heat stress in older individuals and patients with common chronic diseases

Scientists haven predicted that extremes in climate are likely to increase in frequency and severity.(1) These changes may have a direct impact on population health, as heat waves can exceed the physiological adaptive capacity of vulnerable population groups. Individuals over the age of 60 years are consistently the most vulnerable,(2-4) with 82%-92% of excess mortality occurring in this group.(5) Risks for heat-related illness or injuries are compounded for people with obesity,(6,7) cardiovascular disease,(8-10) respiratory disease(8-10) and diabetes mellitus.(4,8,9) These conditions decrease the body's ability to adapt to changes in environmental conditions.(11) When people must perform physical work in the heat, the occurrence of heat-related morbidity and mortality is likely to be more frequent.(12) Although these trends in heat-related morbidity and mortality are evident, there has been little research to explain the causes of increased susceptibility within vulnerable populations. In this review, we describe the effects of heat on human physiology and the factors that increase the risk of heat stress. The methods used in preparing this review are summarized in Box 1 and are described in greater detail in Appendix 1 (available at www.cmaj.ca/cgi/content/full/cmaj.081050/DC1).