A recent study reveals that older adults face the highest risks during heat waves, particularly older women, who are more likely to die from heat-related causes compared to older men. This research has clarified that this disparity stems not from the longer lifespan of women, which often results in a larger population of older women, but rather from physiological vulnerabilities specific to older women.
Conducted by Olivia Leach, a doctoral student in kinesiology at Penn State, alongside her advisor W. Larry Kenney, who is a professor as well as the Marie Underhill Noll Chair in Human Performance, the research indicates that older women and middle-aged women, aged 40 to 64, are more susceptible to high temperatures and humidity than older men. The findings, published in the American Journal of Physiology-Regulatory, Integrative and Comparative Physiology, were somewhat surprising as previous observations showed no such differences in heat vulnerability among adults younger than 30.
The researchers did not directly compare middle-aged men with middle-aged women but noted that the physiological responses of middle-aged women were akin to those of older men, suggesting that middle-aged women experience heightened vulnerability to heat compared to men in the same age bracket.
“This research not only illustrates that middle-aged and older women face increased risks from extreme heat but also outlines what temperature and humidity levels are safe for women as they age,” said Leach. “We have created a temperature/humidity curve that reflects these thresholds according to age, which can be useful in developing policies aimed at protecting people during heat waves.”
The study involved testing the heat thresholds of 72 participants aged between 40 and 92 in a controlled environmental chamber at Kenney’s lab. Participants ingested a small device encased in a capsule to monitor their core temperature throughout the trial.
During the experiment, participants engaged in light physical activities similar to everyday tasks, even in hot conditions. The researchers steadily increased the temperature and/or humidity until the participants’ bodies could no longer maintain a safe core temperature, leading to an increase in their core temperature.
This study is part of the PSU H.E.A.T. (Human Environmental Age Thresholds) project, overseen by Kenney. For five years, the PSU H.E.A.T. project has been investigating the limits of heat and humidity that humans can withstand before their core temperatures rise, which can lead to serious heat-related health issues like heat exhaustion, heat stroke, or death.
“We’re not implying that exposure to a specific temperature guarantees illness or death,” said Kenney. “Instead, we aim to identify the boundaries of human livability — the thresholds beyond which people cannot sustain their normal daily activities. When these limits are reached, it’s crucial for individuals to take steps to cool down, like finding air conditioning.”
Previous studies by Kenney and colleagues have highlighted that as individuals age, their vulnerability to heat increases due to a decline in their ability to sweat and circulate blood to the skin, which are essential for cooling off. Effective sweating and increased blood flow to the skin help in dissipating heat and supporting the process of sweating.
To date, the PSU H.E.A.T. project has conducted over 600 experiments on nearly 200 participants aged 18 to 92. However, this particular study still revealed unexpected findings, according to Leach.
“In younger adults, there is no notable difference in heat vulnerability between men and women,” Leach stated. “Younger individuals tend to be in better health overall, making health metrics like blood pressure and cholesterol levels more consistent compared to older populations.”
Leach elaborated that older adults display a wide range of heat vulnerability.
“We have investigated numerous factors that could explain who is most at risk during heat waves,” Leach explained. “We identified age and biological sex as the two primary factors that predict heat-related risks in healthy adults.”
While factors such as cardiovascular health and certain medications may influence an individual’s sensitivity to heat, the researchers found that age and biological sex are the most significant determinants of heat vulnerability among healthy individuals.
“Other considerations, including cardiovascular fitness or body mass, play a minimal role in determining a person’s heat vulnerability while at rest or during light activity,” Leach added. “Ultimately, older women are indeed at a greater risk from heat compared to others. As governments and community leaders prepare for the increasing frequency of extreme heat, recognizing the vulnerability of older women is crucial in their planning efforts.”
