How Biological Age Tests Compare to Just Tracking Your Fitness Data

What Does a Biological Age Test Actually Measure?

It measures a pattern in your biology that statistically tracks with age and health, then reports that pattern as a number of years. Most consumer tests read DNA methylation, chemical tags on DNA at thousands of sites. The first widely used "epigenetic clocks" were built to predict chronological age (Horvath, 2013; Hannum et al., 2013). Later clocks were trained on health outcomes instead, such as PhenoAge, which was built from clinical blood markers and mortality (Levine et al., 2018), and DunedinPACE, which estimates the pace of aging from decades of follow-up on 19 organ-system measures (Belsky et al., 2022).

For the underlying biology, see what epigenetic age means and whether it can be reversed.

Does a Higher Biological Age Predict Anything Real?

Yes, on average across groups of people. In four cohorts of older adults, each 5-year increase in the gap between methylation age and chronological age was linked to a 21 percent higher mortality risk after adjusting for age and sex (Marioni et al., 2015). Young adults also differ in biological aging well before midlife: in the Dunedin birth cohort, people of the same calendar age varied in a composite of 18 biomarkers, and faster agers were less physically able and looked older to independent raters (Belsky et al., 2015).

How Reliable Is Your Number?

Less than the single clean figure suggests. When researchers ran replicate samples through six prominent epigenetic clocks, technical noise produced differences of up to 9 years between replicates. Retraining the clocks on principal components brought most replicates within about 1.5 years (Higgins-Chen et al., 2022). Which test a provider uses, and whether it uses this kind of fix, matters. Different clocks also give different answers for the same person because they were trained on different targets (Jylhävä et al., 2017).

What Does Fitness Data Tell You Instead?

Fitness measures are direct, repeatable, and have a long record in outcome research. In a meta-analysis, each 1 MET higher level of cardiorespiratory fitness (about 3.5 mL/kg/min of VO2) was associated with a 13 percent lower risk of all-cause mortality (Kodama et al., 2009). In 122,007 adults who underwent treadmill testing, the lowest fitness group had about five times the mortality risk of the elite group, with no upper limit of benefit observed (Mandsager et al., 2018). The American Heart Association has argued that cardiorespiratory fitness should be treated as a clinical vital sign (Ross et al., 2016). Grip strength has a similar association with mortality (Leong et al., 2015).

Fitness metrics are also observational evidence, so they show association rather than proof that raising them extends life. Wearable VO2 max numbers are estimates; lab test versus wearable estimate covers how far to trust them, and VO2 max and longevity goes deeper on the research.

What Is the Most Common Misconception?

That a younger biological age means you are aging well, or that an older one is a diagnosis.

What Should You Do Next?

Spend effort where you can act, and treat the test as optional.

Frequently Asked Questions