Extreme heat can accelerate aging at a cellular level

Heatwaves aren’t just a seasonal inconvenience anymore. They’re longer, hotter, and deadlier than ever before. Millions feel their effects, from power outages to hospital visits.

But beyond the obvious effects of extreme heat – dehydration, heat stroke, and exhaustion – there’s something more insidious happening beneath the surface: accelerated aging.

A new study from the USC Leonard Davis School of Gerontology suggests extreme heat may be speeding up the aging process at the biological level.

It is well documented that extreme temperatures can strain the body, but now, there’s growing evidence that prolonged heat exposure might make people age faster. If true, climate change isn’t just a crisis of weather – it’s a crisis of time itself.

How heat changes the aging process

Aging isn’t just about counting birthdays. A person’s chronological age tells one story, but their biological age? That’s the real measure of health.

Biological age reflects how well cells, tissues, and organs function. When it’s higher than chronological age, disease risks increase, and life expectancy drops.

Jennifer Ailshire, senior author of the study, explained that people living in hotter regions tend to experience faster biological aging than those in cooler areas. Scientists have suspected heat plays a role in declining health, but its direct link to aging has been unclear.

Link between heat and aging

To investigate, the researchers examined data from over 3,600 individuals aged 56 and older, all participants in the Health and Retirement Study.

Over a six-year span, scientists collected blood samples, analyzing them for epigenetic changes – chemical modifications that influence how genes behave. One major process in this field is DNA methylation, which can switch genes on or off without altering the genetic code itself.

Study co-author Eunyoung Choi noted that the team used epigenetic clocks to monitor these molecular shifts. These clocks detect methylation patterns and estimate biological age.

The researchers then compared biological aging rates with historical heat index data from 2010 to 2016, uncovering a strong correlation.

What counts as “extreme heat”?

The National Weather Service defines extreme heat using the heat index – a combination of temperature and humidity.

Extreme heat is broken down into three categories. The “Caution” level ranges from 80°F to 90°F. The “Extreme Caution” category spans 90°F to 103°F. The most dangerous level, simply called “Danger,” starts at 103°F and goes up to 124°F.

This study included all three levels, examining how frequent exposure to each affected biological age. More days of extreme heat meant faster aging at a cellular level.

The pattern remained strong even after adjusting for lifestyle choices, income, and other demographic factors.

Heat exposure alters aging

Where a person lives plays a crucial role in how heat impacts them. Some regions endure long stretches of brutal temperatures, and the effect on residents’ biological aging is staggering.

“Participants living in areas where heat days, as defined as Extreme Caution or higher levels (≥90°F), 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,” Choi said.

“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.”

To confirm their findings, the researchers used three different epigenetic clocks – PCPhenoAge, PCGrimAge, and DunedinPACE.

All pointed to the same conclusion: heat exposure accelerated aging over one to six years. PCPhenoAge even detected changes within weeks or months.

Older adults have a greater risk

Ailshire emphasized that older adults face even higher risks. The study factored in the heat index instead of just air temperature, which proved critical. Humidity can worsen heat’s effects by making it harder for sweat to evaporate, leaving the body struggling to cool down.

“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,” said Ailshire.

“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.”

Since older adults sweat less, they are more prone to heat exhaustion and heatstroke. Prolonged exposure to extreme temperatures may also compromise immune function, increasing vulnerability to illness.

Future research directions

The study raises new questions about how heat reshapes health over time. Scientists aim to pinpoint additional factors that increase vulnerability to heat-driven aging.

They also want to explore whether this accelerated aging process is reversible – or if it permanently alters long-term health outcomes.

Beyond research, the findings signal a need for immediate action. Cities and policymakers may need to rethink urban infrastructure. More shaded walkways, cooling stations, and heat-resistant building designs could become necessities, not luxuries.

Ailshire believes that ignoring the issue is not an option. “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.”

The study is published in the journal Science Advances.

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