Helping our bodies beat the heat

Periods of extreme heat – even one day when the thermometer reaches 35°C – are associated with an increased risk of injury, hospitalization and death. When the body becomes too warm, the heart and kidneys do not function properly. This physiological response to heat can have adverse health effects.

“The risk depends on our body’s ability to defend itself and control internal temperature and blood pressure,” explains Daniel Gagnon, associate professor at the Université de Montréal’s School of Kinesiology and Exercise Science. “Being healthy and physically active provides some protection. But as we age, our body’s ability to dissipate heat decreases, making us more susceptible to heat stroke.”

Two age groups are particularly vulnerable to the effects of extreme heat: young children and people over 70 years of age, especially those with pre-existing conditions. In a recent study, Gagnon compared the effects of extreme heat on healthy young adults and seniors with and without heart disease.

The results were striking: More than a third of seniors with heart disease experienced body dysregulation, with the heart struggling to get enough oxygen to support the effort required by the heat.

Acclimatization is key

Fortunately, the human body is able to acclimatize to heat. But that takes time and regular exposure. Experiments in military and sports research have shown that seven consecutive days of hot baths and 1.5 hours of moderate exercise improved heat tolerance in participants.

To find solutions better suited to the general population, Gagnon and his team experimented with Finnish saunas for seniors with heart disease.

“The participants were able to gradually increase their exposure from two 10-minute sessions to two 15-minute sessions,” Gagnon reported. “They also had increased perspiration, a classic sign of heat acclimatization.”

Although heat adaptation research is still in its infancy, it is advancing rapidly in response to the climate crisis. Gagnon has launched a large-scale study to better understand the health risks associated with extreme heat and plans to recruit 1,000 participants over the age of 18.

“The results, which will be available in a few years, will deepen our understanding of the underlying mechanisms and help us develop more targeted prevention strategies,” he said.

Tips for staying cool

In the meantime, here are Gagnon’s tips for coping with our increasingly hot summers:

• Use an electric fan, a particularly effective method in humid climates such as Quebec. But remember: using a fan can be counterproductive in very low humidity or temperatures above 40° C.
• Sponge yourself regularly with cold water.
• Soak your feet in cold water.
• Stay socially connected (especially important for seniors and the socially isolated).
• Set your air conditioner to 25°C instead of 20°C to build your tolerance for higher temperatures (and reduce energy consumption).