Long-term exposure to extreme heat can make you biologically old, a new study says.
the study, Published in Advances in sciencefound that older people living in hotter regions of the United States showed signs of accelerated aging at the cellular level.
Scientists at the University of Southern California analyzed blood samples from almost 3,700 people over the age of 56 and measured biological age using an epigenetic clock, a tool for analyzing changes in DNA over time. Biological age is determined by a set of DNA markers.
Biological aging is different from chronological aging. Your actual age is determined by the year you lived, but your biological age reflects how quickly your cells and tissues deteriorate.
The researchers compared the biological aging rates of participants with local fever index data from 2010 to 2016. The heat index accounts for both temperature and humidity, which together determines how heat feels in the human body.
The results showed a clear link between extreme heat exposure and faster aging.
Prolonged exposure to fever was associated with an increase of up to 2.48 years of age in biological age, but this was comparable to smoking, the study said.
People experiencing more extreme heat days defined as temperatures above 32.2C age faster at a molecular level and at a higher risk of age-related diseases and early death, the researchers said.
Study participants who live in areas that account for half of the year, such as Phoenix, Arizona, experienced up to 14 months of additional biological aging compared to people living in areas that are heated less than 10 days a year, said Eunyoung Cho, a postdoctoral scholar at USC and a co-author of the study.
“Just because you live in a more heated area, you’re aging biologically faster,” Dr. Choi said.
This link remained even after researchers explained factors such as socioeconomic status and lifestyle habits. “This correlation persisted even after controlling for socioeconomic and other demographic differences, as well as lifestyle factors such as physical activity, alcohol consumption, and smoking,” she added.
Extreme fever is known to increase the risk of immediate health problems, such as heat stroke, but the effects on long-term aging are less clear.
Studies have shown that older biological ages are more vulnerable to conditions such as heart disease, cognitive decline, and frailty.
A new study found that sustained heat exposure could speed up these processes and worsen health outcomes in older adults. Heat stress can cause inflammation and damage to cells, leading to accelerated aging.
“It’s particularly about the combination of heat and humidity in older people, as older people don’t sweat the same way,” said Jennifer Ayrshire, senior author of USC’s gerontology and sociology studies.
“If you’re in a humid location, it doesn’t have much cooling effect. You have to look at the temperature and humidity in your area to really understand what your risk is.”
The findings are because the climate crisis has made extreme fevers more frequent around the world. The number of extremely hot days has increased over the last few decades, with heat waves lasting longer and covering larger areas.
2024 was the hottest on record, with cities across the world shattering temperature records. Heat waves in Europe, North America and Asia have been linked to the deaths of tens of thousands of people in recent years.
Scientists warn that extreme heat will become an even greater public health threat without significantly reducing greenhouse gas emissions.
Elderly people are particularly vulnerable as their bodies struggle to regulate temperature efficiently. As more people age in the warmer world, scientists say they must rethink how cities protect their populations from exposure to chronic fever.
“If it’s warm everywhere, the population is aging and these people are vulnerable, then you need to be really smart about these mitigation strategies,” Dr. Ayrscher said.
Researchers suggest that policymakers and urban planners take extreme heat into consideration when designing cities. Strategies such as increasing green space, providing shaded bus stops and providing access to cooling centres for seniors can help reduce long-term health risks.
