Repeated exposure to heatwaves is accelerating ageing in people, according to a study. The impact is broadly comparable with the damage smoking, alcohol use, poor diet or limited exercise can have on health, the researchers said.
Extreme temperatures are increasingly common owing to the climate crisis, potentially causing widespread and long-lasting damage to the health of billions, the scientists warned.
The research represents a “paradigm shift” in the understanding of the extent and severity of heat’s impact on our health, which can be lifelong, according to one expert.
It was already known that heatwaves cause short-term spikes in early deaths with, for example, almost 600 premature deaths linked to a June heatwave in England. But the new analysis is one of the first to assess the longer-term impact.
The researchers followed 25,000 people in Taiwan for 15 years and compared their exposure to heatwaves with their biological age, a measure of overall health. They found, for example, that biological age increased by about nine days for people who experienced four more heatwave days over a two-year period. Manual workers, who tend to spend more time outside, were strongly affected, with their biological age increasing by 33 days.
While the increase in biological age may seem quite small, the scientists noted that this was only over a two-year period. They are investigating the impact of heatwaves on ageing over people’s entire lifetimes.
The researchers also said that the total impact on populations around the world would be large, because everyone suffers during heatwaves, and higher biological age is a strong predictor of increased risk of death.
“If heatwave exposure accumulates for several decades, the health impact will be much greater than we have reported,” said Dr Cui Guo, at the University of Hong Kong, who led the research. “Heatwaves are also becoming more frequent and lasting longer so the health impacts could be much greater [in the future].” Fossil fuel burning, the main cause of the climate crisis, reached record levels in 2024.
Prof Paul Beggs, at Macquarie University in Sydney, Australia, and not part of the research team, said: “Many of us have experienced heatwaves and survived unscathed – or so we thought. [This research] now shows that exposure to heatwaves affects the rate at which we age.”
He added: “In 2024, [scientists] discovered that early life heat exposure negatively impacts brain white matter development in children. Coupled with the new finding that heatwave exposure accelerates ageing in adults, we have a paradigm shift in our comprehension of the extent and gravity of heat’s impact on our health. The impact can occur at any age and can be lifelong.”
The new research, published in the journal Nature Climate Change, used the results of a series of medical tests, including blood pressure, inflammation, cholesterol, and lung, liver and kidney function, to determine the biological age of each person in the study. The researchers compared this with the actual age of each person to see if their exposure to heatwaves was linked to faster ageing.
They found the total number of heatwave days experienced had the biggest impact on accelerated ageing. Why prolonged high temperatures cause faster ageing is not known, but damage to DNA is likely to be part of the reason.
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Analysis showed that the harmful effect of heatwaves lessened over time, but remained significant. This suggests people were increasingly taking steps to cope with the heat, such as spending more time in the shade and using air conditioning where available.
The 25,000 adults in the study were all part of a paid-for health management plan and were on average younger, healthier and more educated than the general population. Older and sicker people are more vulnerable to heat, so the impact on ageing is likely to be larger than found in the study.
The study took into account people’s weight, smoking and exercise habits, and any pre-existing conditions such as diabetes and cancer, as well as the overall use of air conditioning in their neighbourhood. But data on potentially relevant factors such as time spent outdoors, coolness of housing and individual air conditioner use was not available, with the researchers saying further investigation was needed.
Beggs said the results of the study were broadly consistent with those from a recent US study that showed outdoor heat accelerated ageing among older adults. Another US analysis, from 2023, found that “high exposure to extreme heat was associated with faster cognitive decline for [Black people] and residents of poor neighbourhoods”.
