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.
How does heat accelerate aging?
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.
