As extreme heat waves become more frequent across the United States, new research suggests that rising temperatures could be accelerating biological aging in older adults.
Scientists from the University of Southern California have found that prolonged exposure to high temperatures can speed up biological aging at the cellular level. Their study, published in Science Advances, analyzed data from more than 3,600 adults aged 56 and older.
The study revealed a striking correlation: those living in areas with frequent hot days, such as Phoenix, Arizona, exhibited faster aging markers compared to those in cooler regions.
The key measure in the study was epigenetic aging, which tracks molecular changes in DNA without altering the genetic code.
Researchers used “epigenetic clocks” to analyze DNA methylation patterns, a process that influences gene expression.
The results were clear—older adults who lived in areas experiencing “Extreme Caution” or higher heat days (above 90°F) for half the year showed up to 14 months of additional biological aging compared to those who experienced fewer than 10 heat days annually.
“Even after controlling for several factors, we found this association. Just because you live in an area with more heat days, you’re aging faster biologically,” said study author Eun Young Choi.
The study classified heat days using the National Weather Service heat index, which considers both temperature and humidity. While dry heat is challenging on its own, humidity further compounds the problem by making it harder for the body to cool down.
“It’s really about the combination of heat and humidity, particularly for older adults,” said Jennifer Ailshire, senior author of the study. “Older adults don’t sweat the same way. We start to lose our ability to have the skin-cooling effect that comes from evaporation of sweat. If you’re in a high humidity place, you don’t get as much of that cooling effect.”
This means that states across the South and Midwest, where humid heat is a persistent issue, may see an even greater impact on their aging populations.
Short-term exposure to extreme heat was found to cause immediate biological aging effects.
The most alarming results, however, emerged when researchers analyzed long-term heat exposure over one- and six-year periods.
The study found that chronic exposure to high temperatures was linked to persistent epigenetic changes—potentially increasing the risk of age-related diseases before clinical symptoms even appear.
The implications are particularly concerning as climate change continues to push summer temperatures to record highs.
Scientists estimate that by 2050, more than 100 million Americans could be living in areas where extreme heat events occur regularly.
“Global warming has intensified extreme heat events, posing serious risks to public health,” the researchers noted. “The frequency, intensity, and duration of extreme heat events are expected to grow rapidly in the coming decades.”
The study’s authors explain that this growing issue requires more than personal adaptations like air conditioning and hydration—it demands citywide and nationwide policy changes.
Urban planners and policymakers could play a significant role in heat mitigation strategies, including planting more trees, increasing urban green space, and ensuring shaded public areas like bus stops and sidewalks.
“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,” Ailshire said.