Greater heat exposure may accelerate biological aging

Key takeaways:

• More days of extreme heat over short-, medium- and long-term periods corresponded with biological aging.
• People in areas where heat days of 90°F or above occurred half the year appeared especially vulnerable.

Greater exposure to heat may hasten biological aging in older adults, results from a cohort study published in Scientific Advances indicated.

In some cases, biological aging increased by up to nearly 3 years, researchers reported.

“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,” Jennifer Ailshire, PhD, a professor of gerontology and sociology at University of Southern California (USC) Leonard Davis School of Gerontology, said in a press release.

In the analysis, Ailshire and Eun Young Choi, PhD, a postdoctoral scholar at USC Leonard Davis School of Gerontology, used multiple biological clocks — including PCGrimAge, DunedinPACE and PCPhenoAge — to measure the methylation patterns and determine biological aging of 3,686 American adults aged 56 years or older at several time points.

The researchers then compared these changes in aging with participants’ location’s heat index history and number of heat days, defined as days of 90°F or above, as indicated by 2010 to 2016 National Weather Service data.

The analysis included three levels of heat days, as categorized by the National Weather Service Heat Index Chart. These consisted of the “caution,” “extreme caution” and “danger” levels, where heat index values ranged between 80°F to 90°F, 90°F to 103°F and 103°F and 124°F, respectively.

Ailshire and Choi found that more heat days over 7-day and 30-to-60-day periods corresponded with greater PCPhenoAge acceleration. For instance, a one-unit increase in heat days at the caution level or above over a 7-day period increased PCPhenoAge acceleration by 1.15 years (95% CI, 0.63-1.67).

“This means that 10% more heat days corresponds to a 0.115-year PCPhenoAge acceleration,” they wrote.

Meanwhile, longer-term heat exposure corresponded with higher acceleration for all clocks.

Ailshire and Choi pointed out that a one-unit increase in heat days at the caution level or above over a 1- and 6-year period, respectively, appeared tied to a:

• 0.62- and 1.09-year increase in PCGrimAge acceleration;
• 1.66- and 2.88-year increase in PCPhenoAge acceleration; and
• 3% and 5% faster DunedinPACE rate.

These findings remained consistent in subgroup analyses, although Choi said people living in areas where heat days of 90°F or above occurred half the year “experienced up to 14 months of additional biological aging compared to those living in areas with fewer than 10 heat days per year,” Choi said in the release.

“Even after controlling for several factors, we found this association,” she added. “Just because you live in an area with more heat days, you're aging faster biologically.”

The results “may reflect different magnitudes and types of biological responses to heat stress occurring in varying time frames,” the researchers wrote.

For example, “the observed short- and mid-term associations of heat on PCPhenoAge acceleration may be indicative of immediate physiological responses to heat stress,” they wrote, whereas extended heat exposure “can drive more persistent and extensive changes in physiological deterioration that accumulate over time and are reflected in accelerated biological aging.”

Ailshire noted in the release that they used heat index, as opposed to just air temperature, to take relative humidity into account.

“It's really about the combination of heat and humidity, particularly for older adults, because older adults don't sweat the same way. We start to lose our ability to have the skin-cooling effect that comes from that evaporation of sweat,” she added. “If you’re in a high humidity place, you don’t get as much of that cooling effect. You have to look at your area’s temperature and your humidity to really understand what your risk might be.”

References:

• Choi EY, Ailshire JA. Sci Adv. 2025;doi:10.1126/sciadv.adr0616.
• Study: Extreme heat may speed up aging in older adults. Available at: https://www.eurekalert.org/news-releases/1074317. Published Feb. 26, 2025. Accessed March 19, 2025.