Why do we become less tolerant to heat as we age?

When faced with heat, our bodies have a remarkable ability to defend themselves. As our temperature rises, two mechanisms play a key role: blood flow to the skin increases, and we sweat more. This allows our bodies to release some of the heat they accumulate. But as we age, this remarkable mechanism gradually becomes less effective. The sweating response may decrease. Blood flow to the skin adapts less effectively. And the cardiovascular system also has less capacity to respond to this additional stress. As a result, under the same heat conditions, an older person may accumulate more heat in their body. A recent study illustrates this particularly well. Researchers exposed young adults and people aged 65 and older to extreme heat for 3 hours while having them perform light activities that mimicked those of daily life. Under dry heat conditions at 47 °C, the increase in core body temperature reached: +0.68 °C among those aged 18–39 compared to +1.37 °C among those aged 65 and older. This represents an increase approximately twice as large among older adults under these experimental conditions (McKenna et al., 2023). This is why aging is a major factor in vulnerability during heat waves. But this is not inevitable. As we age, certain principles become even more important: drink regularly without waiting until you’re thirsty, seek out cool environments, limit activities during the hottest hours of the day, adjust the intensity of physical exertion, and remain extra vigilant during heat waves. Because when it comes to heat, we are not all equal. “As we age, we don’t just lose our ability to tolerate heat. We gradually lose some of our ability to get rid of it.”