There is a saying that the heat kills people. In fact, when the temperature rises to around 40 degrees Celsius, human activity becomes difficult, and when it reaches 50 degrees, it has a direct impact on mortality rates. High temperatures combined with high humidity are even more deadly.
Research has shown that prolonged exposure to extreme heat can accelerate aging. While there have been many studies indicating that continuous heat stress has negative effects on various organisms, such as Caenorhabditis elegans, fish, chickens, and mice, there are not many studies confirming its impact on the rate of biological aging in humans.
Researchers from the University of Southern California (USC) published a study in the international journal "Science Advances" on the 27th, analyzing the correlation between the duration of exposure to extreme heat and biological aging in 3,686 adults aged 56 and over. The results showed that longer exposure to extreme heat correlates with an increase in biological age by more than 2 years.
The researchers compared the exposure duration and level of extreme heat for study subjects based on the number of extreme heat days observed in the continental U.S. from 2010 to 2016. Extreme heat levels were categorized into caution (26.7–32.2 degrees), high risk (32.2–39.4 degrees), and danger (39.4–51.1 degrees). Exposure duration was divided into short term (same day as blood sampling, 7 days), medium term (30, 60 days), and long term (1, 6 years).
Biological aging was analyzed by tracking changes in DNA methylation. Methylation refers to a chemical modification where methyl groups (CH₃) attach to DNA in response to changes in the surrounding environment. As time goes on, methylation increases. By analyzing the level of DNA methylation, one can estimate biological age.
The research found that prolonged exposure to extreme heat accelerates biological aging. Across all levels of extreme heat, an increased number of days exposed to extreme heat led to faster progression of biological aging. Particularly, those exposed to extreme heat for long periods were found to be, on average, 2.48 years older than others.
The researchers noted that this study confirmed that continuous heat stress negatively affects human DNA methylation. If heat stress is short-lived, its impact on aging may be limited, but if it continues for an extended period, physiological anomalies accumulate and influence DNA.
The researchers also examined the impact of socioeconomic inequality on exposure to extreme heat. People with fewer assets or insufficient physical activity tended to reside in areas with more extreme heat days. Black individuals, Hispanics, and those with lower education levels were also found to have more days of exposure to extreme heat. The researchers remarked, "We confirmed significant differences in the exposure patterns to extreme heat among demographic groups," adding that "the findings from this study will serve as crucial evidence for establishing policies to respond to climate change."
References
Science Advances (2025), DOI: https://doi.org/10.1126/sciadv.adr0616