Extreme heat may speed up biological ageing in older people

Extreme heat seems to speed up biological ageing in older people, suggesting that it could raise the risk of age-related diseases.

“This is one of the first large-scale studies to link long-term heat exposure to biological ageing in humans,” says Eun Young Choi at the University of Southern California. “Older adults living in areas with more extreme heat days aged biologically faster than those in cooler regions.”

Choi and her colleagues analysed genetic data extracted from blood samples collected by other researchers in 2006-7 from 3600 people across the US. All were aged 56 and over at the time.

They estimated each participant’s biological age using three so-called epigenetic clocks, which involves looking at patterns of chemical tags called methyl groups on DNA. These patterns alter as we get older and such changes have been linked to age-related diseases.

The researchers also examined daily air temperature readings taken within a few kilometres of where participants lived for the six years before blood samples were taken.

They found that, for roughly every 200 days in that six-year period that participants were exposed to daily maximum temperatures of at least 32.2°C (90℉), their biological age was up to 3.5 months older, on average, than those in cooler areas. That figure varied depending on which clock was used.

“This points to heat exposure increasing the speed of biological ageing,” says Austin Argentieri at Harvard University, who wasn’t involved in the study.

Previous studies on people in Taiwan and Germany have also found a link between extreme heat exposure and biological ageing.

But epigenetic clocks don’t perfectly capture the ageing process or people’s risk of diseases, says Argentieri. “More work that can tie together both exposure to extreme heat, biological ageing from these clocks, and the influence on age-related diseases, mortality or lifespan itself, would really help drive home what we should take away from this.”

What’s more, the study didn’t account for access to air conditioning or how long participants spent outdoors, which would alter their personal exposure to heat, says Argentieri. The team did control for other factors such as age, sex, race, wealth, ethnicity, smoking status, alcohol consumption, obesity and physical activity.

Further studies should explore whether the results translate to younger people, or those living in different countries where people may have different approaches to keeping cool, says Argentieri.

Pinpointing who is at most risk of ageing faster due to extreme heat could help policymakers develop and deploy measures to protect them, he says.