Extreme heat is a growing concern, especially for older adults, as global temperatures continue to rise. The year 2024 marked a critical juncture, with the global average temperature surpassing the 1.5 C threshold set by the Paris Agreement. This has led to more intense heatwaves, posing significant health risks, particularly to the elderly. The vulnerability of older adults to heat is a pressing issue, especially in regions like Quebec, where the aging population is set to reach a quarter of the total population by 2031. This article delves into the reasons behind the increased susceptibility of seniors to extreme heat and explores potential solutions, including a promising new discovery that could help them adapt. (https://theconversation.com/topics/the-grey-revolution-182247)
Why Older Bodies Struggle with Heat
The primary health effects of heat are linked to excessive heat buildup in the body. Older adults experience a more pronounced increase in internal body temperature compared to young adults when exposed to heat. This change begins gradually in adulthood and continues to develop with age. Research has shown that for the same level of heat exposure, internal body temperature tends to increase by approximately 0.1°C per decade of life. For instance, a 90-year-old could reach an internal body temperature nearly 0.7°C higher than a 20-year-old under similar conditions. This explains why older adults are more prone to cardiovascular and kidney complications due to heat. (https://pubmed.ncbi.nlm.nih.gov/37410904/)
To prevent overheating, the body employs various mechanisms. Blood vessels in the skin widen to exchange more heat with the environment, a process known as cutaneous vasodilation. Sweat glands produce sweat, which cools the body through evaporation. However, these responses become less effective with advancing age. Studies have shown that starting at age 40, people generally sweat less, and skin vasodilation is reduced during heat exposure. (https://pubmed.ncbi.nlm.nih.gov/24349447/)
A crucial question remained: Does aging also affect the nerve signals the brain sends to trigger these protective mechanisms? In other words, is the neural control of thermoregulation impaired with age? This was the focus of recent research, which aimed to answer this question. (https://physoc.onlinelibrary.wiley.com/doi/10.1113/JP290417)
How to Better Tolerate Heat
Repeated exposure to heat can trigger physiological adaptations that allow the human body to better tolerate hot environments. This phenomenon, known as heat acclimation, is widely used by athletes and military personnel before competitions or deployments in hot regions. Acclimation involves exposing oneself to heat for 60 to 90 minutes a day over a period of seven to 14 days, either through exercise or passive methods like hot baths or saunas. (https://pmc.ncbi.nlm.nih.gov/articles/PMC10988689/)
The benefits are significant: sweating begins more quickly and becomes more profuse, blood vessels in the skin dilate sooner, resting internal body temperature decreases, and the heart doesn't have to work as hard during heat exposure. As a result, the body experiences fewer adverse effects for the same level of heat exposure. Many of these adaptations occur within the first week, a phenomenon known since the late 1700s and applicable to everyone. (https://books.google.ca/books?hl=en&lr=&id=BpIXAQAAMAAJ&oi=fnd&pg=PR1&ots=cnL66jTCD4&sig=zoD5xtOXrBuNcjop5T8-GIpsOfk)
This strategy could be particularly useful in early summer in northern climates, when the first heat waves strike before the body has naturally adapted to high temperatures. However, until recently, the scientific community had limited data on how older adults maintain this adaptive capacity. (https://pubmed.ncbi.nlm.nih.gov/36862716/)
Hot Baths as a Solution
To address this, researchers compared the physiological responses to heat of 15 older adults (aged 60 to 78) with those of 16 young adults (aged 21 to 40) before and after seven days of heat acclimation involving daily 90-minute hot baths at 40°C. Before and after the baths, nerve signals responsible for sweating and blood vessel dilation were measured. After seven days of acclimation, these signals were activated more quickly, meaning the body triggered heat-loss mechanisms while accumulating less heat. This response was associated with earlier sweating and cutaneous vasodilation. (https://physoc.onlinelibrary.wiley.com/doi/10.1113/JP290417)
Interestingly, these adaptations were comparable in young and older adults. This finding suggests that aging does not necessarily impair the nervous system's ability to adapt to heat. However, questions remain. The study's demanding protocol of seven daily 90-minute baths at 40°C raises concerns about feasibility on a large scale. Future research must identify simpler, more accessible heat acclimation strategies to help older adults adapt to extreme heat. (https://journals.physiology.org/doi/full/10.1152/japplphysiol.00105.2026)
In conclusion, the rising global temperatures and their impact on older adults demand urgent attention. The discovery of heat acclimation through hot baths offers a promising solution, but further research is needed to make it accessible and effective for the elderly population. As the world grapples with the challenges of a warming planet, understanding and addressing the unique vulnerabilities of older adults to heat is crucial for their well-being and survival.
