Biological ageBio age

Biological age is an attempt to say how well or badly your body has weathered the years you have lived, using measurements rather than your birth date. Two people at 50 can be a decade apart in health, and calendar age cannot see that difference.

There are two broad families, and they are not equally trustworthy. Clinical marker scores are computed from ordinary blood results with published coefficients, so you can see exactly what drove the number. Epigenetic clocks read DNA methylation patterns from a saliva or blood sample and hand back a number whose workings are opaque to the person who paid for it.

The clinical family has a decent pedigree. An analysis of 9,389 adults from a US national survey, followed for 18 years, compared five biological age algorithms and found they predicted mortality better than chronological age did. The Phenotypic Age equation our calculator implements comes from that lineage, using nine standard blood markers plus your age.

Both families were built and validated at population level, and that is the fine print that matters. Predicting mortality across thousands of people is not the same skill as telling one person whether their last six months of habits worked, and the second claim is the one being sold.

For consumer epigenetic tests, reviews in the ageing literature are blunt: different clocks disagree on the same person, results move with sample handling, tissue, processing pipeline and even time of day, and the measurement noise is comparable in size to the effect people hope to detect. The field's own position is that they do not meet the standard for individual decisions.

Used sensibly, the number is a motivational summary of things you could have read individually anyway. A biological age above your calendar age is a prompt to look at the inputs behind it, blood pressure, glucose, lipids, inflammation, fitness, rather than a diagnosis, and the useful response is to change an input and re-measure in a year.

In practice, our phenotypic age calculator shows the working, and the pace of aging index scores the lifestyle inputs rather than the biology. Neither is a verdict, and any test that offers you one for a fee is overselling.

Sources

• Levine ME. Modeling the rate of senescence: can estimated biological age predict mortality more accurately than chronological age? J Gerontol A Biol Sci Med Sci 2013;68:667-674
• Levine ME, et al. An epigenetic biomarker of aging for lifespan and healthspan. Aging 2018;10:573-591
• From population science to the clinic? Limits of epigenetic clocks as personal biomarkers