Long periods of extreme heat can accelerate biological age, scientists say
Longer periods of extreme heat has been found to accelerate biological age in older adults by up to two years, according to new research.
More heat days over time correlated with deterioration at the molecular and cellular level in adults 56 years or older, likely because the biological deterioration accumulates over time and eventually leads to disease and disability, Eunyoung Choi, a postdoctoral associate at the University of California's Leonard Davis School of Gerontology, told ABC News.
Researchers at the University of Southern California studied blood samples from 3,686 adults starting at an average chronological age of 68 years with varying socioeconomic backgrounds across the U.S. and compared epigenetic aging trends to the number of extreme heat days in the participants’ places of residence, according to a study published Wednesday in Science Advances.
"Epigenetic age is one way we measure biological aging, which tells us how well our body is functioning at the physical, molecular and the cellular levels," Choi said. "...We know that some people seem to age faster than others, and that's because biological aging doesn't always match chronological age."
Regression modeling showed that more heat days, or longer-term heat, over one and six years increased biological age by 2.48 years. Short and mid-term heat also increased biological age by 1.07 years, according to the paper.
Extreme heat was defined as the daily maximum heat index -- derived from both temperature and humidity -- with a "caution" range of between 80 degrees to 90 degrees Fahrenheit and an "extreme caution" range of between 90 degrees and 103 degrees Fahrenheit, in accordance with the National Weather Service, according to the paper. "Extreme danger" was defined as any heat index level over 124 degrees Fahrenheit.
The researchers compared the epigenetic age of participants from regions with long periods of extreme heat to those living in cooler climates. There was a 14-month difference in epigenetic age between residents living in places like Phoenix, Arizona, than milder places like Seattle, even after accounting other individual and community-level differences, like income, education, physical activity and smoking, Choi said.
"Two people that had identical sociodemographic characteristics and similar lifestyles, just because one is living in a hotter environment, they experience additional biological aging," she said.
The 14-month differences is comparable to effects seen with smoking and heavy alcohol consumption -- two well-established risk factors of accelerated biological aging, the researchers found.
DNA methylation -- the process of chemical modification to DNA that tends to change as people age -- is "highly responsive" to environmental exposures like social stress, pollution and, in this case, extreme heat, Choi said.
Previous research has linked extreme heat to serious health risks like cardiovascular disease, kidney dysfunction, hospitalization and even death, Choi said. But prior to this research, scientists did not fully understand what is occurring at the biological level before those health issues appear, Choi added.
"The physical toll of the heat might not show up right away as a diagnosable health condition, but it could be taking a silent toll at the cellular and the molecular level," Choi said.
It's important to uncover potential hidden effects of heat on the body because it can serve as an "important precursor" before they turn into more serious health conditions, Choi said.
"We can intervene at the earlier stage," she added.
Humidity also plays a big role in how the body responds to heat, especially for older adults, Choi said.
"As we age, our bodies don't cool down as rapidly," she said.
The new research provides a foundation for the development of targeted public health interventions, the researchers said.
"This provides strong evidence critical for guiding public policy and advocacy initiatives aimed at developing mitigation strategies against climate change," Choi said.
ABC News Medical Unit's Dr. Jessica Yang contributed to this report.
