A groundbreaking new study published in Science Advances has discovered that exposure to high temperatures can speed up biological aging processes in older adults. This could potentially explain the long-established link between extreme heat and increased health risks.
Connecting Climate Change to Cellular Aging
Researchers from the University of Southern California’s Leonard Davis School of Gerontology analyzed data from a nationally representative sample of 3,686 U.S. adults aged 56 and older. They examined how ambient outdoor heat affects “epigenetic aging,” a molecular marker of biological aging based on DNA methylation patterns throughout the genome.
“While we’ve known that extreme heat contributes to hospitalization, cardiovascular disease, and death, especially among older adults, we didn’t fully understand the biological mechanisms behind these effects,” explains lead author Eun Young Choi. “Our study bridges this gap by examining how heat exposure alters the pace of aging at the cellular level.”
How Researchers Defined “Hot”
The study didn’t rely on temperature alone to measure heat exposure. Instead, researchers used the Heat Index (HI), which combines temperature and humidity to reflect how hot it actually feels to the human body. This is an important consideration since humidity impairs the body’s ability to cool itself through sweating.
Following National Weather Service guidelines, they categorized heat into specific thresholds:
- Caution level: Heat Index from 80°F to 90°F (26.7°C to 32.2°C)
- Extreme caution level: Heat Index between 90°F and 103°F (32.2°C and 39.4°C)
- Danger level: Heat Index between 103°F and 124°F (39.4°C and 51.1°C)
The researchers measured “heat days”—days when the heat index reached or exceeded these thresholds—over different periods. They noted that none of the participants lived in areas that experienced the most severe “extreme danger” level (above 124°F/51.1°C) during the study period.
Short-Term and Long-Term Heat Exposure Effects
The study measured heat exposure over various time windows, from the day of blood collection to periods spanning up to six years prior.
What they discovered was striking:
- Short-term heat exposure (7-30 days) was associated with accelerated PCPhenoAge, one measure of biological aging
- Long-term heat exposure (1-6 years) was linked to accelerated aging across all epigenetic clocks measured
- For PCPhenoAge specifically, heat at the “caution” level over 7 days was associated with aging 1.15 years faster
- Heat at the “extreme caution” level over 6 years was associated with a 2.88-year increase in biological age
Everyone is Vulnerable
Interestingly, the researchers found these effects consistent across different sociodemographic groups. Despite analyzing subgroups by age, gender, race/ethnicity, education, and wealth, they found no strong evidence that any particular group was more vulnerable to heat-related epigenetic aging than others.
“This is somewhat surprising,” notes co-author Jennifer Ailshire. “It suggests that extreme heat may be a universal risk factor for accelerated aging regardless of one’s social or economic position.”
Why It Matters
This research provides new insights into how climate change might impact public health beyond the immediate dangers of heat waves. The epigenetic changes observed represent subtle biological deterioration that precedes the development of diseases and disabilities.
As extreme heat events’ frequency, intensity, and duration are projected to increase with global warming—potentially affecting more than 100 million Americans by 2050—understanding these biological mechanisms becomes increasingly important for public health planning.
The study is particularly notable for using a nationally representative sample, high-resolution climate data covering the entire contiguous United States, and accounting for participants’ relocations. This approach provides a comprehensive picture of how heat affects aging across diverse populations and geographic regions.
Protecting Vulnerable Populations
While the study doesn’t directly address prevention strategies, the findings underscore the importance of heat mitigation efforts, particularly for older adults whose thermoregulatory functions naturally decline with age.
Public health experts recommend several approaches during extreme heat events:
- Staying in air-conditioned environments when possible
- Maintaining proper hydration
- Limiting outdoor activities during the hottest parts of the day
- Checking regularly on elderly neighbors and relatives
As our planet continues to warm, understanding the biological underpinnings of heat-related health risks will be crucial for developing targeted interventions to protect vulnerable populations.
