How quickly is your body aging, and what factors beyond your own genetics make the most difference in the result?
Recent studies from the USC Leonard Davis School of Gerontology highlight how environmental and social factors, such as heat exposure and education, play a major role in shaping biological aging. At the same time, new advances in measuring biological age, including the development of a novel tool known as Physiological health Age (PhysAge), are giving scientists better ways to understand these effects.
Biological aging refers to how the body is changing over time, including how well organs and systems are working. For example, two people who are both 65 may look very different inside: One may have the biological profile of someone younger, while another may show signs of aging earlier.
“Biological age gives us a clearer picture of health than chronological age. It helps us understand who is likely to stay healthy longer and who may be at higher risk for disease and disability,” says USC University Professor Eileen Crimmins.
Crimmins is a pioneer in the field of biodemography, or the linking of biological measurements to large amounts of population data. Recent research led by Crimmins, her USC Leonard Davis School colleagues and their trainees has shed light on how social factors may be more deeply entwined with human biology and health outcomes than previously thought.
Heat Exposure May Accelerate Aging
A February 2025 study led by USC researchers found that extreme heat may speed up the biological aging process for older adults. The study examined data from more than 3,600 participants in the national Health and Retirement Study. Blood samples taken at various time points during a six-year period were analyzed for epigenetic changes, or changes in the way individual genes are turned “off” or “on” by a process called DNA methylation.
Researchers discovered that older adults living in U.S. counties with more days of extreme heat had higher biological ages than peers of the same chronological age in cooler areas. 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, says first author Eunyoung Choi, a USC Leonard Davis PhD in Gerontology alumna and postdoctoral scholar.
Choi notes that participants living in high-heat areas like Phoenix, where “Extreme Caution” heat days (with temperatures of 90 degrees or above) occur half the year, experienced up to 14 months of additional biological aging compared with those living in areas with fewer than 10 heat days per year.
“Even after controlling for several factors, we found this association,” she says. “Just because you live in an area with more heat days, you’re aging faster biologically.”
The study adds to evidence that climate change could have long-term health consequences beyond immediate risks such as heatstroke. The next steps for the researchers will be to determine what other factors might make someone more vulnerable to heat-related biological aging and how it might connect to clinical outcomes.
In the meantime, the study results could also prompt policymakers, architects and others to keep heat mitigation and age-friendly features in mind as they update cities’ infrastructure, from placing sidewalks and bus stops in shaded areas to planting more trees and increasing urban green space, says Jennifer Ailshire, senior author of the study and professor of gerontology and sociology at the USC Leonard Davis School.
“If everywhere is getting warmer and the population is aging, and these people are vulnerable, then we need to get a lot smarter about these mitigation strategies,” Ailshire says.
Education Linked to Slower Biological Aging
Another USC-led study, published in August 2025, showed that higher levels of education are associated with slower biological aging. Using data from the U.S. Health and Retirement Study, researchers examined how years of schooling were related to DNA methylation-based measures of biological age.
They found that individuals with more education tended to have lower biological ages than peers with less education, even when they were the same chronological age. Importantly, the relationship held even after accounting for differences in income, suggesting that education and its associated life circumstances have a lasting impact on health.
“Education shapes opportunities and risks throughout life,” says Crimmins, who authored the study with former USC Leonard Davis postdoctoral researcher Mateo Farina, now an assistant professor at the University of Texas at Austin, and Jung Ki Kim, a USC Leonard Davis research associate professor. “It’s a powerful social determinant of health, and it is leaving a mark on how fast or slow our bodies age.”
This finding highlights how social and behavioral factors leave marks that can be detected in the biology of aging. Access to education not only affects career and economic outcomes but also appears to extend into the cellular processes that determine longevity and healthspan.
A New Tool to Measure Biological Aging
Understanding the links between environmental exposures and biological aging requires complex tools. A September 2025 study led by USC Leonard Davis Research Associate Professor Thalida Em Arpawong and colleagues introduces one such tool: Physiological health Age (PhysAge).
PhysAge is a DNA methylation–based measure that combines information from eight biological systems, including immune, cardiovascular, respiratory, renal, metabolic and endocrine functions. Unlike earlier epigenetic clocks, which were trained primarily on mortality data, PhysAge was designed around established clinical biomarkers such as glycated hemoglobin, cholesterol, inflammation and lung function.
In testing, PhysAge was as effective as or better than widely used epigenetic clocks like GrimAge and DunedinPACE in predicting frailty, disability, cognitive decline and mortality. Because it reflects specific systems, it can also indicate which areas of health are most affected.
“Our goal was to create an interpretable clock that not only represents the overall physiological health state but also provides insight into which of its constituent systems may be driving accelerated aging,” Arpawong says. “PhysAge allows us to connect environmental and behavioral exposures to the specific biological systems and inform us about which ones may be at greater risk and require closer clinical monitoring and earlier intervention.”
Together, these studies illustrate how biological aging is shaped by more than just genetics or the passage of time. Environmental stressors such as heat exposure and social factors such as education leave measurable effects on the body’s molecular aging processes.
Tools like PhysAge make it possible to detect these effects and provide more information on health impact. For example, heat stress may accelerate cardiovascular and kidney aging, while education may help preserve metabolic or immune health. By identifying these physiological pathways, researchers can better understand why certain groups are more vulnerable and how interventions might slow biological decline.
Implications for Public Health
The ability to measure biological aging has practical implications for both health care and policy.
If heat exposure is shown to consistently accelerate biological aging, then urban planning measures to address heat risks could become recognized as interventions that not only improve comfort but also protect long-term health, Ailshire notes.
Similarly, education policy can be understood as health policy. Investments in early and lifelong education may contribute to healthier aging across the population. With measures like PhysAge, researchers and policymakers could eventually quantify the benefits in terms of years of biological life preserved.
As climate change accelerates and populations age, the intersection of environment, inequality and biology will become an increasingly urgent area of study. The hope is that with better measurement tools and clearer understanding of risk factors, scientists, clinicians and policymakers can take steps not only to extend lifespan but also to improve healthspan — the years of life lived in good health.
“We’re experiencing increased life expectancy, but this additional time is largely time spent living with disease,” Crimmins says. “To increase healthspan, we have to intervene much earlier in the process of health change. Knowing more about how social factors interact with biology can tell us how to best intervene.”
