As global temperatures rise and extreme heat waves become more frequent, a new study reveals that women—especially older women—are at greater risk from heat-related health issues than men.
The research, conducted by a team from Penn State and published in the American Journal of Physiology-Regulatory, Integrative and Comparative Physiology, identifies key physiological differences that leave women more vulnerable during heat waves.
IMPACT OF HEAT ON WOMEN: A PHYSIOLOGICAL DIFFERENCE
This groundbreaking study, led by Olivia Leach, a doctoral candidate in kinesiology, alongside her adviser, Professor W. Larry Kenney, is the first to determine that women’s vulnerability to heat stems from physiological differences rather than the fact that women generally live longer than men. The research highlights that women aged 40 to 64 are as vulnerable to extreme heat and humidity as men aged 65 and older.
Middle-aged and older women are particularly susceptible to heat-related illnesses, such as heat exhaustion and heat stroke, due to a reduced ability to cool themselves compared to men of the same age. The researchers observed that women experience heat vulnerability at lower temperature and humidity combinations than men, increasing their risk during extreme heat events.
UNDERSTANDING THE DISPARITY
According to Leach, the results were somewhat unexpected, as there is no notable difference in heat vulnerability between men and women under 30. However, as people age, their ability to regulate body temperature deteriorates. While older men experience this decline, women experience it earlier and at lower thresholds.
“The physiological responses of middle-aged women closely resembled those of older men,” said Leach. “This discovery shows that middle-aged women are more vulnerable to heat than middle-aged men.”
The study tested heat thresholds of 72 participants between the ages of 40 and 92 in a controlled environmental chamber. Each participant swallowed a capsule that measured their core temperature throughout the experiment as researchers gradually increased the chamber’s heat and humidity while participants performed light physical activities to mimic daily tasks. The experiment continued until the participants’ bodies could no longer regulate their temperature effectively.
EXTREME HEAT’S EFFECT ON OLDER WOMEN: WHAT THE DATA SHOWS
This study is part of the PSU H.E.A.T. (Human Environmental Age Thresholds) project, which has tested over 200 participants in more than 600 experiments. The project’s goal is to determine the combination of heat and humidity that humans can tolerate before their core temperatures rise, increasing the risk of heat-related illnesses.
For older women, the study found that their ability to sweat and pump blood to the skin—two mechanisms vital for cooling—diminishes more rapidly than in men. Sweat evaporation helps dissipate heat, while increased blood flow to the skin allows the body to cool more effectively. Without these mechanisms functioning properly, older women are left particularly vulnerable.
A CURVE TO PREDICT HEAT VULNERABILITY IN WOMEN
One of the key findings of this study is the creation of a temperature/humidity curve to predict heat vulnerability based on age and sex. “We now know what levels of heat and humidity are dangerous for older women, and this data can inform public policy to protect at-risk populations during heat waves,” said Leach.
This predictive model could help governments and healthcare providers plan for future heat waves, identifying at-risk individuals who may need extra assistance or access to cooling centres during times of extreme heat.
PHYSIOLOGICAL DIFFERENCES IN MEN AND WOMEN
Dr. Kenney, the study’s senior author, explained the significance of these findings. “We’re not saying that everyone who reaches a certain temperature will get sick or die, but we are highlighting the limits of livability,” Kenney said. “People need to take steps to cool their bodies when they reach these temperature thresholds, such as seeking air conditioning or reducing physical activity.”
Previous research had already established that age decreases a person’s ability to regulate body temperature effectively. However, this new study emphasizes that sex is a significant factor in heat vulnerability, with women being at a much higher risk, especially as they age.
POLICY IMPLICATIONS FOR PROTECTING VULNERABLE POPULATIONS
As climate change makes extreme heat waves more frequent, public health policies must evolve to protect vulnerable groups. “Governments and social leaders need to factor in the vulnerability of older women when planning for heat waves,” Leach said. This is particularly important as many older adults may live alone and be unaware of the heightened risks they face.
“Older women are at a greater risk from extreme heat, and this information needs to be part of heat wave response strategies,” Leach added. The study provides valuable data that could influence city planning, healthcare guidelines, and emergency services, especially in regions where heat waves are becoming more common.
THE SURPRISING FINDINGS IN YOUNG ADULTS
Interestingly, the study found no significant difference in heat vulnerability between younger men and women. “Young adults tend to be healthier, and factors like blood pressure and cholesterol are more consistent across sexes,” said Leach. This uniformity in health metrics may explain why younger people do not show the same vulnerability disparity.
However, as people age, the variance in health measures increases. “Older adults have a wider range of vulnerability to heat, but age and biological sex are the two most important factors predicting heat risk,” Leach explained. Cardiovascular fitness and body mass play a much smaller role in determining heat vulnerability, especially for older women.
FUTURE RESEARCH AND BROADER IMPLICATIONS
The PSU H.E.A.T. project has already made significant strides in understanding how the human body responds to extreme heat, but Leach and Kenney believe there is much more to learn. They plan to continue testing and expanding their database, focusing on how factors like medication and pre-existing health conditions may affect heat tolerance.
Additionally, researchers are examining how socioeconomic factors, such as access to air conditioning, influence heat-related risks. They hope to use this data to inform public health efforts, particularly in regions where cooling systems are less accessible.