Editor's take: Long stretches of extreme heat may do more than make you miserable. A new study suggests they can accelerate the body's natural aging process. Researchers in Taiwan tracked nearly 25,000 adults over 15 years and found that just two years of repeated exposure to heat waves could push a person's biological age forward by the equivalent of eight to 12 extra days.
The findings, published in Nature Climate Change, add scientific weight to growing concerns about the health toll of steadily warming temperatures. "This small number actually matters," Cui Guo, an assistant professor at the University of Hong Kong who led the research, told The New York Times. "This was a study of a two-year exposure, but we know heat waves have actually been occurring for decades."
In the study, a heat wave was defined either as at least two consecutive days of abnormally high temperatures or as a period when Taiwanese officials issued heat warnings. The researchers examined each participant's exposure over time, pairing climate records with detailed health data.
To measure aging, scientists compared participants' chronological age with their biological age – a metric based on 12 biomarkers linked to organ function and cellular health. These markers, which include measures of liver, lung, and metabolic performance, provide a snapshot of how the body is aging beyond the calendar years.
By controlling for outside factors such as smoking, exercise, and preexisting conditions, the researchers were able to isolate heat exposure as a driver of accelerated aging.
The results showed that age itself can compound the risks. Older individuals were more susceptible to biological changes from heat than younger individuals, even under similar exposure conditions. Living without air-conditioning or working outdoors also increased vulnerability.
Guo emphasized that the study does not suggest individuals are losing literal days off their lifespan. Instead, the effect reflects subtle but measurable shifts in biological aging – shifts that could signal higher disease risks over time.
The findings come after years of intensifying heat. In 2024, recorded as the hottest year globally, human-driven climate change was responsible for 41 additional days of extreme heat worldwide, according to World Weather Attribution, a network of climate scientists.
This year, record-breaking heat has disrupted life across several regions. The US West has endured severe temperatures, while Iran experienced conditions that officials described as nearly unlivable. Europe, Japan and Korea all suffered widespread heat emergencies in recent weeks, and France is debating how the use of air-conditioning squares with its climate goals after experiencing two heat waves this summer.
The Taiwanese research is not alone. Earlier this year, a separate analysis of about 3,600 older Americans found that living in conditions of 90 degrees Fahrenheit for roughly 140 days each year could equate to as much as 14 months of extra biological aging. That study, however, did not adjust for health habits like smoking or exercise, which may affect results.
Kristie Ebi, a professor at the University of Washington who studies climate and health but was not involved in the research, said that capturing those details is important. "The results may have implications for public health interventions," she said, noting that aging is closely tied to both mortality and disease risk.
Ebi noted that governments are already experimenting with ways to reduce exposure risks. In Oregon, for example, Medicaid allows people with conditions made worse by heat to use program funding to purchase an air conditioner. But she cautioned that air-conditioning cannot be considered a perfect solution, since its energy demand contributes to warming.
Over the long run, some populations may adapt to higher temperatures. The Taiwan study found modest evidence that as more households gained air-conditioning units over the study period, the impact of heat on aging diminished slightly. But that adaptation may not be enough to offset the overall growth in extreme heat events.
Scientists also warn that high temperatures worsen other health risks, from air pollution to the ignition of wildfires and other climate-linked disasters. "People just have low awareness that heat kills or that, in this case, has adverse health consequences," Ebi said. "That's just been a persistent challenge."