Extreme heat is making us age faster. Here's how

CNN

3 days ago

The soupy, smothering extreme heat that has scorched parts of the Northern Hemisphere this summer takes a hard toll on our bodies. It can make you feel nauseous, woozy and dehydrated. It can have pernicious health effects on multiple organs.
But there's another, less well-known, impact of extreme heat: It makes you age faster.
Prolonged exposure to soaring temperatures can cause a deterioration in our cells and tissues and speed up biological aging, according to a new and growing body of research.
Chronological age refers to how long a person has lived, but biological — or 'epigenetic' — age measures how well our tissues and cells function. The difference between the two explains why sometimes someone's age does not seem to match their health and vitality.
An accelerated biological age is the 'canary in the coal mine' for future risk of earlier onset of diseases such as cancer, dementia and diabetes, and early death, said Jennifer Ailshire, professor of gerontology and sociology at the University of Southern California Leonard Davis School of Gerontology.
As climate change forces people to endure increasingly severe and longer lasting heat waves, scientists say there is an urgency to better understand the ways heat is slowly and silently undermining human health at a cellular level.
Our DNA is set at birth; it is the blueprint for how the body functions and cannot be changed.
But the way DNA is expressed — the way this blueprint is carried out — can be affected by external factors that trigger chemical modifications that turn genes on or off like a light switch.
External factors affecting these switches include behaviors, such as smoking and lack of exercise, as well as environmental factors, like heat.
Heat stresses the body, making it work harder as it tries to cool down, which can damage cells. While a little bit of heat stress can be good for the body, helping increase resilience, prolonged exposure taxes the body over extended periods and can have long-term consequences.
Research on animals has pointed to strong associations between heat and accelerated aging but, until recently, there were very few studies that looked at humans.
Ailshire is one of the scientists trying to change that. She and another researcher, Eunyoung Choi, published the first population-scale research into this area in February.
They analyzed blood samples taken from a group of more than 3,600 people across the United States aged 56 and above. They used tools called 'epigenetic clocks,' which capture the way DNA is modified and provide an estimate of biological age. They then linked this to daily climate data in participants' locations in the years before the blood samples were taken.
Their results, published in February, found people who experienced at least 140 extreme heat days a year — when the heat index, a combination of temperature and humidity, was above 90 degrees Fahrenheit — aged up to 14 months faster than those in locations with less than 10 extreme heat days a year.
This link between heat and biological aging remained even when taking into account individual factors such as exercise levels and income, although the study did not look at access to air conditioning or time spent outside.
The strength of the association was significant, too. The results showed extreme heat had the same impact on aging as smoking or heavy alcohol use.
Their findings are supported by other recent research.
A 2023 study of more than 2,000 people in Germany found medium- and long-term exposure to heat was linked to accelerated biological aging. The impacts were particularly pronounced in women, who can be more vulnerable to heat as they tend to sweat less, meaning it's harder for them to cool down. People with diabetes or obesity were also more at risk, the study found.
The effects can even start before birth.
A 2024 study looked at accelerated biological aging in children in Kenya who were exposed to drought as fetuses. During pregnancy, their mothers endured heat, as well as dehydration and emotional distress.
These factors can cause stress at a cellular level that needs to be repaired, which means less energy is available for other vital functions, potentially leading to accelerated aging, the study found. Heat stress can also reduce blood flow to the uterus and placenta.
'So we see an impact on growth that includes lower birth weights and an overall harder start to life — all of which can be reflected in faster biological aging,' said Bilinda Straight, a study author and a professor at the School of Environment, Geography, and Sustainability at Western Michigan University.
Thiese findings do not mean that everyone living in hot places will experience accelerated aging, Ailshire said. Each person has their own risk factors and there are ways to adapt.
Access to cooling and avoiding exercise in the hottest parts of the day are important. Better nutrition, more exercise (in the cool parts of the day) and medication can also help, she added. Scientists have found drugs including metformin, prescribed for diabetes, and weight-loss medication Ozempic could slow aging.
If people can change or find ways to adapt to their heat exposure levels, it may be possible to slow or reverse the accelerated aging process, Ailshire said. 'Because that's not permanent damage; it's an indicator of the potential for permanent damage. It doesn't necessarily signify that this damage has been done.'
The area of study is very new. 'We are just at the start of understanding this process, particularly in humans,' Rongbin Xu, a research fellow at the School of Public Health and Preventive Medicine at Monash University in Australia.
But as places warm up, and heat records continue to be smashed, scientists are going to have a lot more data about the myriad ways heat affects our bodies — and who is most vulnerable.
'If we can't do anything about rising temperatures, then at a minimum, we need to be increasing awareness and finding strategies,' Ailshire said.
'There has to be a way that we can get through this.'