Extreme heat may have a bigger impact on biological ageing than smoking and drinking alcohol, research suggests.
As climate change fuels rising temperatures worldwide, a new study warns that extreme heat could be speeding up the ageing process in older adults.
Seniors exposed to prolonged periods of extreme heat showed signs of increased biological ageing, according to the study published in the journal Science Advances this week.
Researchers from the University of Southern California examined data from more than 3,600 people aged 56 and older across the United States, comparing their biological markers to temperature patterns in their local environments.
Their findings? Those living in areas with frequent days above 32°C – classified as “Extreme Caution” or higher by the US National Weather Service – had an accelerated biological age, sometimes by more than a year.
What is biological ageing and why does it matter?
Unlike chronological age, which counts the years since birth, biological age reflects the wear and tear on the body at a cellular and molecular level. A higher biological age than chronological age is linked to an increased risk of disease and premature death.
For the study, researchers analysed blood samples collected over a six-year period from 2010 to 2016, including from participants in hot regions such as Arizona.
Scientists then measured their ages using epigenetic clocks – tools that track changes in DNA over time – and cross-referenced the results with local heat index data, which accounts for both temperature and humidity.
The results showed that those in hotter climates had faster-moving epigenetic clocks, even after accounting for lifestyle factors like exercise, smoking and alcohol consumption.
The hidden dangers of heat and humidity
While high temperatures alone are harmful, humidity compounds them.
“It’s really about the combination of heat and humidity, particularly for older adults, because older adults don’t sweat the same way,” explains USC gerontology professor Jennifer Ailshire, a senior author of the study.
“We start to lose our ability to have the skin-cooling effect that comes from that evaporation of sweat.”
In humid conditions, sweat evaporates more slowly, reducing the body’s ability to cool itself. “You have to look at both temperature and humidity to really understand your risk,” Ailshire adds.
Climate change, urban heat and vulnerable populations
With global temperatures on the rise, the findings highlight the urgent need to protect vulnerable populations – particularly seniors – from heat-related health risks.
According to the World Meteorological Organization (WMO), 2024 was the warmest year on record, about1.6°C above pre-industrial level. Heatwaves are also becoming more frequent and severe.
Previous research has linked extreme heat tocardiovascular stress, kidney problems and even cognitive decline. WHO estimates that heat kills more than175,000 Europeans each year, and without intervention, climate change could lead to2.3 million additional deaths across Europe by 2099.
As this latest study suggests, the risks for older populations could be even greater than previously understood.
“If everywhere is getting warmer and the population is ageing, and these people are vulnerable, then we need to get a lot smarter about [our] mitigation strategies,” Ailshire says.
The researchers emphasised that cities could lessen the impact of extreme heat by increasing urban green space, planting more trees and designing public infrastructure with heat resilience in mind.
Without such measures, rising temperatures could pose an even greater threat to the world’s ageing population in the decades to come.
