Heat-ready before summer

Summer is coming. For older Australians, heatwaves are a genuine health risk.

As we age, we sweat less and move less blood to the skin, so the body holds on to heat. Research from Canada suggests passive heat may help.

The study

The University of Ottawa's Human and Environmental Physiology Research Unit published this in Medicine and Science in Sports and Exercise in 2025.

Twelve active older men, median age 68, sat in water at about 40 °C for roughly 90 minutes a day for seven days.

Before and after, they cycled in a hot, dry chamber set to 40 °C, while the team measured exactly how much heat their bodies released.

What they found

After the week of warm water, the men shed more heat during exercise. Their core temperature was about 0.3 °C lower and their heart rate about 11 beats per minute lower.

The authors suggest passive heat acclimation could be an alternative for older adults who cannot do strenuous exercise in the heat.

What it does not show

Twelve active men, no comparison group, carefully supervised. It does not prove protection during a real heatwave, and it did not include women.

Practical steps before summer

• Build heat exposure gradually in spring, not in the middle of a heatwave.
• Sauna or warm water sessions, kept comfortable, are a reasonable way to do that.
• Hydrate well, and stop if you feel dizzy or unwell.
• Keep a heatwave plan: a cool room, fluids, and someone checking in.
• If you are frail or have heart or kidney disease, speak with your GP.

Free: The Norge Longevity Guide. Heat, cold and light after 50, with the evidence and the safety rules in one place. Get the guide.

Sources

1. Janetos et al., Short-Term Warm Water Immersion for Improving Whole-Body Heat Loss in Older Men, 2025
2. Full text, Medicine and Science in Sports and Exercise

This article is general information, not medical advice. If you have a heart condition, low blood pressure or are pregnant, speak with your GP before using heat or cold.