Your biological age test gives you a number.
But how much can you trust the result?
There are different ways to estimate biological age. Some methods combine clinical and physiological measurements. Others use molecular markers such as DNA methylation or telomere length, while newer computational approaches can analyze much larger sets of biological data.
These methods do not all measure the same biological information, and their reliability depends on several factors.
First, the measurements themselves need to be reliable.
The review by Bafei and Shen discusses telomere length as one example. Telomeres shorten with age and have been widely investigated as potential aging biomarkers. But different laboratory methods can produce different measurements, and measurement error can affect the result.
The same principle applies more broadly: a biological-age calculation can only be as reliable as the biological data used to produce it.
The type of biological-age test also matters.
An epigenetic aging clock, for example, estimates age from patterns of DNA methylation. Some epigenetic clocks were originally developed to predict chronological age, while later clocks were designed to provide information related to health outcomes or mortality.
A test that predicts chronological age very accurately is therefore not automatically the test that tells us most about biological aging or future health.
Validation is another important part of reliability.
Researchers can test biological-age models against outcomes such as morbidity, mortality and functional decline. Across the studies reviewed by Bafei and Shen, some biological-age measures provided information about these outcomes beyond chronological age alone.
But the results were not consistent across every method, population or outcome. A model that performs well in one study may not perform equally well in another.
This is why two tests both described as “biological age tests” can have very different scientific foundations.
When looking at a biological-age result, three questions are useful:
- Were the underlying measurements reliable?
- Has the method been validated in appropriate populations?
- What has the test actually been shown to predict?
There is currently no universally accepted biological-age test that provides a definitive measure of an individual’s overall biological age.
