Biological age is now considered a better reflection of your real health than the number of candles on your birthday cake. Two people born in the same year can age at very different rates. Longevity science is trying to measure that difference precisely.
Biological age and chronological age: what is the difference?
Chronological age is counted in years since birth. It moves forward at the same pace for everyone. Biological age, on the other hand, measures the actual state of your cells and tissues.
According to the reference definition (Moqri et al., Cell 2023), biological age corresponds to the level of age-related biological changes, summarised as a single number. That number indicates the age at which an average person in the reference population would show the same level of molecular and cellular damage.
In other words, your biological age can be lower or higher than your chronological age. It is precisely this gap that interests preventive medicine.
Biomarkers of ageing, the basis of measurement
To objectify biological age, researchers rely on biomarkers of ageing. The Biomarkers of Aging Consortium (Cell 2023; Nature Medicine 2024) defines them as a quantitative parameter that, alone or in combination, predicts biological age and ideally its changes in response to interventions.
These markers are numerous and cover several organs. Metabolic tests (fasting glucose, HbA1c, insulin, lipid profile) are among the measurements considered mandatory in longevity clinics. They are complemented by inflammation (CRP, ESR), cardiopulmonary function (VO2max on an exercise test) and body composition.
This multi-tissue approach is essential. Work on "organ clocks" (Yi Tian, Nature Medicine 2023), carried out on 143,423 individuals aged 39 to 73, shows that an organ never ages alone: organs interact, from healthy to diseased profiles.
The biological clock, an increasingly precise tool
The idea of a biological clock took a major step forward with epigenetic clocks, based on DNA methylation. The first generation (Horvath, Genome Biology 2013; Hannum, Molecular Cell 2013) directly estimated chronological age.
Later generations focused on health and mortality. PhenoAge (Levine, Aging 2018) and GrimAge (Lu, Aging 2019) predict the risk of death. DunedinPACE (Belsky, eLife 2022) measures the very pace of ageing.
These clocks produce an "age" that is compared with actual age. A positive gap, called epigenetic age acceleration, signals faster-than-average ageing.
From biological age to healthspan
Measuring biological age is not a cosmetic exercise. The goal is to act on healthspan, meaning the number of years lived in good health, and not only on lifespan.
The data support this approach. A dose-response meta-analysis (Ding, Lancet Public Health 2025) shows that reaching 7,000 steps a day rather than 2,000 is associated with a marked reduction in all-cause mortality (HR 0.53) and in dementia risk (HR 0.62). Physical activity is also linked to a slower epigenetic clock (Shan, submitted data: N = 156,474).
Sleep matters too. Compared with 8 hours, short sleep (< 7 h) is associated with higher mortality (HR 1.14; Ungvari, Geroscience 2025).
Supporting the biological terrain
These findings fit into a global preventive vision. Improving movement, sleep and circulation helps maintain the "biological terrain" on which biological age rests. Manual approaches, such as lymphatic drainage, are part of this lifestyle approach that supports tissue function.
Ultimately, biological age offers a more faithful reading of how we age than the calendar. Measuring it gives you a concrete starting point for preserving your health over the long term.