Estimating biological age starts with deciding what to measure.
Researchers use biomarkers of aging — measurable biological characteristics that provide information about aging and can be combined to estimate biological age.
These biomarkers can come from very different parts of our biology.
Clinical and physiological measures may include blood pressure, lung function and measures of kidney function, together with blood biomarkers such as glucose, cholesterol, albumin and markers of inflammation.
At the molecular and cellular level, researchers can examine DNA methylation, gene activity, telomere length and other biological changes associated with aging.
Some biological-age models combine many different clinical and laboratory measurements. Others are built mainly around one type of biological information, such as DNA methylation.
But not every measurement that changes as we get older is necessarily a useful biomarker of aging.
Researchers have proposed several criteria for selecting aging biomarkers. Ideally, a biomarker should provide information about aging beyond chronological age alone, reflect underlying aging processes rather than simply the presence of disease, and be suitable for reliable and repeated measurement.
Which biomarkers are selected can directly influence the biological-age estimate.
A model based mainly on routine clinical measurements may capture different information from one based on DNA methylation or other molecular markers. The mathematical method used to combine those biomarkers can also affect the final result.
There is currently no single biomarker or standardized set of biomarkers accepted as the definitive way to estimate biological age.
Research continues to examine which biomarkers — and which combinations of biomarkers — provide the most useful information about biological aging and aging-related health outcomes.
