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• Posted February 27, 2025

Extreme Heat Might Accelerate Aging Among Seniors

Exposure to extreme heat might accelerate aging in older adults, with sizzling weather causing them to fade faster, a new study suggests.

People living in neighborhoods with more days of high heat experience greater biological aging on average than people living in cooler climes, researchers reported Feb. 26 in the journal Science Advances.

“Participants living in areas where heat days, as defined as Extreme Caution or higher levels (90 degrees Fahrenheit or greater), occur half the year, such as Phoenix, Arizona, experienced up to 14 months of additional biological aging compared to those living in areas with fewer than 10 heat days per year,” lead researcher Eunyoung Choi, a postdoctoral scholar at the University of Southern California School of Gerontology, said in a news release.

Biological age tracks declining function in a body’s cells and systems, as opposed to chronological age based on a person’s birthdate, researchers explained in background notes.

Having a biological age that’s greater than one’s chronological age is associated with a higher risk of death and disease, researchers said.

For this study, researchers examined the biological age of more than 3,600 people 56 and older participating in a study of health and retirement. Participants are located throughout the U.S.

Blood samples were taken from participants at various times during the six-year study period, and these were analyzed for epigenetic changes -- changes in the way individual genes are turned “off” or “on.”

Researchers used these changes to calculate an “epigenetic clock” for each person in the study, providing an estimate of their biological age.

The team then compared people’s biological ages to the amount of heat they endure where they live, as reported by the National Weather Service between 2010 and 2016.

The NWS provides three categories for hot days -- “Caution” for 80 to 90 degrees, “Extreme Caution” for 90 to 103 degrees, and “Danger” for anything between 103 and 124 degrees.

This heat index takes into account relative humidity as well as air temperature, senior researcher Jennifer Ailshire, a professor of gerontology and sociology at the USC School of Gerontology, noted.

People living in places with more extreme heat exhibited greater biological aging, even after accounting for other factors like physical activity, alcohol consumption and smoking, researchers said.

“It's really about the combination of heat and humidity, particularly for older adults, because older adults don't sweat the same way,” Ailshire said in a news release. “We start to lose our ability to have the skin-cooling effect that comes from that evaporation of sweat.”

In a high humidity place, there's less of a cooling effect. "You have to look at your area’s temperature and your humidity to really understand what your risk might be,” Ailshire said.

In other words, you're aging faster biologically simply because you live in an area with more heat days, Choi added.

The results remained consistent across three different epigenetic clocks used in the study, researchers said.

Researchers next plan to investigate other factors that might make some more vulnerable to heat-related biological aging, and how this aging might affect a person’s overall health.

City planners and policymakers also might consider ways to reduce the impact of heat on seniors, Ailshire said, providing more shade, planting more trees and increasing urban green space.

“If everywhere is getting warmer and the population is aging, and these people are vulnerable, then we need to get really a lot smarter about these mitigation strategies,” she concluded.

More information

The U.S. Centers for Disease Control and Prevention has more on heat and older adults.

SOURCE: University of Southern California, news release, Feb. 26, 2025