Larger exposure to extreme heat can accelerate biological aging in older adults

A new USC Leonard Davis School of Gerontology study suggests that further exposure to extreme heat may promote biological aging in older adults, raising new concerns about how climate change and heat waves affect long-term health and aging at the molecular level.

Jennifer Ailshire, professor of gerontology and sociology at USC Leonard Davis School, said that neighbors experiencing more high fevers exhibit greater biological aging on average.

Biological age is a measure of how well the body functions at the molecular, cellular and system levels, as opposed to age based on birth date. Larger biological age than age is associated with higher risk of illness and death. Extreme heat exposure itself has long been associated with negative health outcomes, including increased risk of death, but the link of heat to biological aging is unknown.

Measurement of epigenetic changes

Ileshire and her co-author, Yunyoung Choi, gerontology graduate and postdoctoral scholar USC Leonard Davis, examined how biological age changed in analyses of Age Agency at various times, employed at various times, where over 3,600 Health and Retirement Study (HRS) participants (HRS) were photographed at US blood samples taken at age 6 and above. “Off” or “On” by a process called DNA methylation.

Researchers analyzed methylation patterns using a mathematical tool called epigenetic clocks and estimated biological age at each time point. The changes in the biological age of participants were then compared with the history of the Heat Index reported by the National Weather Service from 2010 to 2016, and the number of days of fever.

The National Weather Service Heat Index Chart classifies the values ​​of the heat index into three levels based on the potential risk of adverse health effects. The “caution” level includes thermal index values ​​ranging from 80°F to 90°F, the “extreme attention” level includes values ​​between 90°F and 103°F, and the “hazard” level includes values ​​between 103°F and 124°F. All three levels were included as hot days of study.

The analysis shows a significant correlation between neighborhoods with more extreme heat days and those experiencing greater biological age increases, Choi said. 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.

“Participants living in areas such as Phoenix, Arizona where hot days occur in six months, defined as extreme attention or higher levels (≥90°F), experienced up to 14 months of additional biological aging compared to areas living in hot areas with less than 10 days a year,” she said. “We've found this connection even after controlling for a few factors. Just because you live in an area with more hot days, you're aging biologically faster.”

All three epigenetic clocks employed in this study (pcphenoage, pcgrimage, and dunedinpace) revealed this association when analyzing epigenetic aging over a period of 1-6 years. Pcphenoage also shows association after short (7 days) and medium (30-60 days) periods, indicating that heat-related epigenetic changes can occur relatively quickly, some of which may accumulate over time.

Climate impact on communities

Elderly people are particularly vulnerable to the effects of high fever, Ayrscher said. She noted that in this study, using a heat index rather than just temperature, taking into account relative humidity when analysing the results.

“As older people don't sweat the same way, it's especially about the combination of heat and humidity in older people. They start to lose their ability to have the skin cooling effect that comes from sweat evaporation,” she explained. “If you're in a humid location, it doesn't have much of a cooling effect. You have to look at the temperature and humidity in your area to really understand what your risk is.”

The next step for researchers is to determine other factors that could make them more vulnerable to heat-related biological aging and how they lead to clinical outcomes. In the meantime, the findings could encourage policymakers, architects and others to keep heat reduction and age-friendly features in mind when updating urban infrastructure, with bus stops in mind, with more trees in mind and with more urban green space in mind, Ailshire said.

“If it's getting warm everywhere, if the population is getting older and these people are vulnerable, then you need to be really smart about these mitigation strategies,” she said.