Heat doesn’t just leave us exhausted — it could be ageing us faster. A new study from the University of Southern California suggests that prolonged exposure to extreme heat speeds up biological ageing, with effects, particularly pronounced in older adults.
The research, which involved nearly 3,700 participants with an average age of 68, examined how long-term heat exposure influences the body’s ageing process at a genetic level. The findings were striking: individuals who endured more days of intense heat showed accelerated ageing, with some experiencing the equivalent of up to 2.48 extra years of biological ageing over a six-year period.
How heat accelerates ageing?
Ageing is a natural process, but the rate at which it occurs varies. Environmental factors like sleep deprivation and stress can influence how quickly our bodies deteriorate over time. Heat is now emerging as another critical factor.
Sustained exposure to high temperatures doesn’t just cause immediate health issues—it alters how our genes function. While DNA remains unchanged throughout life, gene expression — how genes are switched on or off — can be influenced by environmental stress. This process, known as epigenetics, plays a crucial role in ageing.
The most well-documented form of epigenetic regulation is DNA methylation (DNAm) — a mechanism by which chemical compounds attach to DNA and modify gene activity without changing the genetic code itself. Heat stress can alter DNAm patterns, affecting the body’s ability to repair itself and regulate vital functions, ultimately leading to faster biological decline.
What the study found?
To measure the impact of heat exposure, researchers tracked participants' geographical locations from 2010 to 2016 and analysed the intensity of heatwaves they experienced. They used the U.S. heat index to classify heat levels into three categories: Caution (temperatures up to 32°C), Extreme caution (32–39°C), and Danger (39–51°C). This classification helped researchers assess the extent of heat exposure and its correlation with biological ageing.
Blood samples were analysed for epigenetic changes across thousands of genome sites. Researchers then applied three widely recognised biological ageing clocks — PcPhenoAge, PCGrimAge, and DunedinPACE — to determine how much faster individuals were ageing compared to the normal rate.
The study revealed a clear connection between prolonged heat exposure and accelerated ageing. Using three established biological ageing clocks, researchers found that participants exposed to higher temperatures experienced faster ageing rates. The PcPhenoAge clock indicated an additional 2.48 years of ageing over the six-year study period, while the PCGrimAge clock showed 1.09 years of extra ageing.
The DunedinPACE clock, which measures shorter-term ageing effects, recorded a smaller but still notable increase of 0.05 years. These findings suggest that rather than ageing the expected six years over the study period, some participants effectively aged up to 8.48 years due to prolonged heat exposure.
What this means for the future?
As global temperatures continue to rise, heatwaves are becoming more frequent and severe. Countries like Australia, where extreme heat events are already intensifying, may face an increased burden of heat-related ageing and health risks. Although past research has linked heat to epigenetic changes in animals such as fish, chickens, and mice, human studies have been limited. This study helps fill that gap, reinforcing the need for further investigation into how prolonged heat exposure affects the human body at a molecular level.
The study's methodology strengthens confidence in its results, given its large and diverse sample size and use of the heat index rather than simple air temperature readings. However, researchers acknowledge some limitations—they did not account for whether participants had air conditioning or spent extended periods outdoors. Despite these findings, much remains unknown about how humans can adapt to heat-induced biological changes. A 2020 review of environmental epigenetics found only seven studies on the subject, with most focusing on cold exposure rather than heat.
(With inputs from PTI)