Biological age

An estimate of how old your body appears to be based on measured markers rather than your birth date, useful as a summary and often oversold as a verdict.

What the term covers

Biological age is not one measurement. It is a family of estimates built by finding which markers predict mortality or disease, then expressing the result on a scale of years because years are intuitive.

The best validated blood based version is PhenoAge, published by Levine in 2018. It uses nine standard markers, including albumin, creatinine, glucose, CRP, lymphocyte percentage, mean cell volume, red cell distribution width, alkaline phosphatase and white cell count, plus chronological age.

What it predicts

PhenoAge predicts all-cause mortality, cardiovascular death and cancer mortality better than chronological age alone, and it does so across multiple independent cohorts. That is a real result, not marketing.

It works because it is a weighted summary of organ function, inflammation and metabolic state. Nothing mysterious is happening, which is a point in its favor.

Where the concept gets abused

Three places. First, precision: an estimate derived from population statistics is not accurate to the year for an individual. Second, reversibility: improving a marker changes the estimate, but the estimate is a summary rather than the thing itself, so the change is not automatically a change in outcome. Third, causation, since the equation was fitted to predict, not to explain.

Used properly it is a good conversation starter. An estimate several years above chronological age usually points at something specific: inflammation, glucose handling, kidney function or a blood count worth investigating.

Baseline's phenotypic age calculator implements the published PhenoAge equation with correct unit conversion, and shows the coefficients so the number is auditable rather than magic.

References

  1. Levine ME, et al. An epigenetic biomarker of aging for lifespan and healthspan. Aging (Albany NY). 2018.
  2. Liu Z, et al. A new aging measure captures morbidity and mortality risk across diverse subpopulations. PLoS Med. 2018.
  3. Jylhava J, Pedersen NL, Hagg S. Biological age predictors. EBioMedicine. 2017.