Biomarkers of biological aging are measurable features researchers use to study age-associated biological change. They may include molecular patterns, physiological measurements or combinations of variables. They are attempts to capture aspects of aging beyond the number of birthdays a person has had.

There is no single universal biological-age meter

A DNA-methylation clock, a protein-based score and a physical-function assessment measure different things. Two tests can disagree without either being fraudulent: they may use different populations, tissues, algorithms or outcomes. Even a technically reliable test needs evidence that its result means what the user thinks it means.

The original multi-tissue epigenetic clock demonstrated that DNA-methylation patterns could estimate age-related information across tissues. Its predictive performance did not establish that changing the clock necessarily changes lifespan or disease risk. Horvath, 2013

Three questions help evaluate a biomarker

First, is it measured consistently? A useful result should not be dominated by sample handling or laboratory variation. Second, does it predict a meaningful outcome? Third, if an intervention changes the marker, does that reliably predict improved health? The third question is the hardest and is essential before treating a marker as a substitute for a clinical endpoint.

Blood measurements can also be influenced by temporary illness or changes in blood-cell composition. A test result should be interpreted in its measurement context, not as a precise count of years added or removed from life.

How to read “age reversal” headlines

A lower score after an intervention may be a finding worth investigating. It is not automatically evidence of rejuvenated organs, reduced mortality or longer life. Those require their own data.

Biological-aging biomarkers are promising research tools. Their value increases when claims remain specific about what was measured, how reproducible it was, and which outcomes have actually been validated.