Biological age: why a single number settles nothing
There are many estimates of biological age and they disagree with each other. What to do about it, and what to watch instead.
Biological age is an attempt to describe, in one number, how far a body has travelled along ageing. The idea is easy to follow: the calendar is the same for everyone, bodies are not. The trouble starts when that number is read as a verdict or as a prize.
Why the estimates disagree
Biological age is not measured — it is estimated, by a model. There are many models, built on different inputs: some on blood chemistry, some on physical measures, some on epigenetic marks. Each carries its own assumptions and its own training population, so two calculators can legitimately return different numbers from the same lab panel. That is not one of them being broken; they are answering slightly different questions.
What to do about it
Watch the direction, not the absolute value — and only inside a single model. "Three years younger" between two different methods means nothing. The same estimate, computed twice six months apart by the same method, does say something.
And remember the model computes from what you gave it. A missing marker does not make the result more honest; it makes it more confident than it deserves to be.
A longer explanation of how these estimates are built is in Biological age: what it is and how it is measured.
Articles in this section are educational and are not medical advice, a diagnosis, or a prescription. Consult a qualified professional before acting on anything you read here.
Read next
- ResearchMedicine and treatment
Rasonque (daraxonrasib): the FDA has approved the first broad RAS(ON) inhibitor — what it changes and what it does not
On 26 August the FDA approved the first drug in the class of broad RAS(ON) inhibitors, for metastatic pancreatic cancer. Median overall survival rose from 6.7 to 13.2 months. We go through the figures from primary sources, name the toxicity alongside the effect, and include the criticism — including the criticism the investigators raised themselves.
7 min read 
ExplainerMedicine and treatmentAmblyopia after ten: what the trials of treatments beyond patching found
Parents of a child older than seven are told two opposite things: that it is too late, and that a new method changes everything. What the trials in this age group actually found — glasses alone, patching and atropine, binocular games, levodopa — which age ranges regulators authorised and on what data, and what these studies do not say.
16 min read
ExplainerBiomarkersVitamin D after sixty: what the large trials in older adults found, and why the guidelines disagree
"Vitamin D for the elderly", "how long can you take it", "all year round?" — these are questions about regimen, not deficiency. What changes in the body after sixty, what VITAL, D-Health, DO-HEALTH and STURDY found on fractures, falls and mortality, why large infrequent doses produced more falls in several trials — and how two guidelines read the same blood test differently.
22 min read