OTTAWA — People over the age of 60 are the most vulnerable to heat waves, with 82% to 92% more deaths than average occurring in this age group.

Risks for heat-related illness or injury – such as heat stroke, heat exhaustion and heat cramps – also heighten in people with obesity, heart disease, diabetes and respiratory conditions, as these ailments decrease the body’s ability to adapt to temperature changes.

A review by Professor Glen Kenny from the Faculty of Health Sciences at the University of Ottawa and by coauthors, published in CMAJ (Canadian Medical Association Journal), describes the effect of heat on human physiology and the factors that increase the risk of heat stress.

Laboratory-based physiologic studies show that, compared with younger people, otherwise healthy older individuals are less able to detect heat; in addition, they respond more slowly physiologically to heat with adequate blood distribution and sweating to cool the body. Their ability to respond to thirst is also delayed, and they take longer to recover from dehydration. People from lower socio-economic groups, those with lower levels of education and those who are socially isolated have a greater risk of mortality.

Housing may be a factor, as lower-income people often live in crowded or poor-quality housing, with inadequate ventilation and cooling systems. In fact, air conditioning is associated with a risk reduction of 80% and working fans with a 30% reduction. Homeless people are at risk because they lack shelter from extreme heat and because they often have underlying physical or psychiatric issues as well.

Still, there are gaps in knowledge that warrant further research.

“It will be essential to discern whether impairment in thermoregulatory capacity exists in terms of the whole-body response and not simply in terms of local heat-loss responses (sweating and/or skin blood flow),” write Professor Kenny and his coauthors. “New research should focus not only on filling these gaps in the science-based information, but also on developing clinical guidelines for health professionals to facilitate the giving of advice to patients.”