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Scientists have long known that people age at different rates biologically. Someone who is 70 years old on paper may have the health of a much younger person, while another 70-year-old may be much more frail than their same-age peers. A new study sheds light on the underlying biology behind epigenetic clocks biological aging measurements that have become popular tools for capturing exactly this variation.
What Epigenetic Clocks Biological Aging Tests Actually Measure
These lab tests have become popular tools for studying biological aging, or how the body’s cellular function changes at a faster or slower rate than expected. However, the underlying biology behind each of these measurements has remained largely unknown until now. A USC Leonard Davis School of Gerontology-led study published in npj Aging shows the variability in what five of the most widely used epigenetic clocks are actually measuring.
How Researchers Investigated These Clocks
The researchers examined combined epigenetic and transcriptomic measurements to compare gene expression and identify the biological pathways highlighted by each of five epigenetic clocks, an approach that let them look beyond the raw age predictions each clock generates to understand what’s actually driving those numbers.
Distinct Pathways Behind Each Epigenetic Clocks Biological Aging Measurement
They found that each aging clock was associated with different biological processes, from energy balance and cellular growth to immune cell activation and inflammatory signaling. Even though the clocks emphasized different biological pathways, they shared several common themes, including changes in the immune system, metabolism and cell communication, all well-known features of aging.
Why This Variability Matters for Research Applications
For example, one clock may be better for studying treatments that target the immune system, while another may be better for testing therapies that improve metabolism or slow the decline in physiological resilience. This distinction offers researchers a practical framework for selecting which specific clock best matches the biological process their intervention is designed to target.
New Prediction Tools Emerging From This Epigenetic Clocks Biological Aging Research
The researchers further used the analysis to create new tools called transcriptomic aging gene scores, or TAGS. The combined approach provided an even clearer picture of a person’s biological health; in several cases, TAGS predicted health outcomes such as frailty, walking speed, heart disease, diabetes, lung disease and death better than the epigenetic clocks alone.
What Stronger Predictive Power Means in Practice
TAGS outperforming the original epigenetic clocks on real-world health outcomes suggests that combining DNA methylation data with gene expression activity captures aging-related biological signal that methylation measurements alone may miss, potentially offering researchers and clinicians a more sensitive tool for identifying individuals at elevated risk before symptoms become apparent.
Illuminating the “Black Box” Behind Epigenetic Clocks Biological Aging
The research team also developed new gene-expression based clocks to complement existing epigenetic clocks, which show even stronger predictive power for age-related disease and mortality. By linking DNA methylation changes with gene expression activity, senior author Eileen Crimmins said the study has further illuminated the “black box” of biological aging that these popular clocks have represented until now.
Why This Matters for the Broader Aging Research Field
The work also helps explain the biology behind tools that are becoming increasingly common in aging research, giving scientists a clearer conceptual foundation for interpreting results generated by the five clocks examined and potentially informing how future epigenetic clocks are designed and validated going forward.
What This Epigenetic Clocks Biological Aging Research Means Going Forward
Given that each clock captures distinct biological pathways despite sharing common aging-related themes, researchers designing future aging intervention studies may need to select their measurement tool more deliberately based on the specific biological process, whether immune function, metabolism, or cellular growth, their treatment targets. Given TAGS’s demonstrated stronger predictive power for real-world outcomes like frailty and mortality, this new tool could eventually complement or even supersede some existing epigenetic clocks in both research and, potentially, future clinical applications.
What to Watch Going Forward
As researchers continue validating TAGS against larger and more diverse populations, the aging research field will likely watch for follow-up studies testing whether this gene-expression-based approach maintains its predictive advantage across different demographic groups and health conditions. Given the study’s success in explaining what previously functioned as a “black box,” this epigenetic clocks biological aging research may prompt renewed interest in developing next-generation biomarkers that combine multiple molecular data types rather than relying on DNA methylation measurements in isolation.
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