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Biological age is a ranking
Tests disagree
Different tests use different modalities, such as blood work or sleep and stress patterns from a wearable, and they can point in opposite directions. One may suggest a person is a little older while another says a little younger.
Use for consumers
For consumers, the risk is optimizing biomarkers that can be disconnected from actual health and from how a person feels. The value for them lies in the trends, which can encourage better sleep and better eating.
Use in drug development
For drug development, the same markers carry real weight. An objective marker that is not perfect can still help design a clinical trial protocol and support drug discovery.
Some companies have even checked the biological age of their employees to see whether they were overworked, since aging that rises a bit too fast might be a sign of heading toward burnout.
Why can biological age tests disagree?
Each clock is trained to predict something different. Steve Horvath's 2013 clock was trained to predict calendar age from methylation. PhenoAge, from Morgan Levine's group in 2018, was trained on blood markers linked to mortality. GrimAge, published in 2019, predicts time to death. DunedinPACE, from Daniel Belsky's team in 2022, estimates the pace of aging.
Why do drug trials want aging biomarkers?
The diseases of aging take decades to appear, so a trial that waits for them in healthy adults needs very long follow-up. A validated biomarker that moves sooner could shorten that. Mouse lifespan studies already run two to three years. Researchers use markers like methylation clocks as stand-ins until longer outcomes can be measured.
How could aging markers flag burnout?
Chronic stress changes the methylation pattern of some genes. A 2015 study by Anthony Zannas and colleagues in Genome Biology linked lifetime stress to faster epigenetic aging. Stress hormones act on cells through receptors that regulate gene activity. The study followed an urban cohort in the United States.
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