Biological Age

Definition

Biological age is an estimate of an individual's physiological state relative to population norms for the same chronological age. It operationalizes ageing as accumulated functional decline across systems, rather than time since birth, and is typically expressed as an "age gap" between biological and chronological age.[1][2][3]

How It Is Estimated

Researchers estimate biological age using multivariate models built from clinical chemistry panels, functional tests, and molecular biomarkers such as DNA methylation. "Aging clocks" integrate these data to predict outcomes like mortality risk or functional decline, but they are model-dependent and may reflect different aspects of ageing biology.[4][5][6][7]

Interpretation

A biological age higher than chronological age is associated with elevated risk for age-related disease and mortality in cohort studies, whereas a lower estimate can reflect resilience or slower ageing trajectories. Individual interpretation requires context about measurement variability, population reference ranges, and the specific clock used.[2][8][9]

References

1. Hamczyk, M. R., et al. (2020). Biological versus chronological aging: A review. https://www.lidsen.com/journals/geriatrics/geriatrics-03-02-051
2. Rollandi, G. A., et al. (2019). Biological age versus chronological age in the prevention of age-related diseases. https://www.lidsen.com/journals/geriatrics/geriatrics-03-02-051
3. Salih, A., et al. (2023). Conceptual overview of biological age estimation. https://pmc.ncbi.nlm.nih.gov/articles/PMC10187689/
4. Johnson, A. A., & Shokhirev, M. N. (2024). Contextualizing aging clocks and properly describing biological age. https://pmc.ncbi.nlm.nih.gov/articles/PMC11634725/
5. Horvath, S. (2013). DNA methylation age of human tissues and cell types. https://doi.org/10.1186/gb-2013-14-10-r115
6. Levine, M. E. (2020). Assessment of epigenetic clocks as biomarkers of aging in basic and population research. https://pmc.ncbi.nlm.nih.gov/articles/PMC11634725/
7. Belsky, D. W., et al. (2022). Aging clocks & mortality timers: A window to measuring biological age. https://pubmed.ncbi.nlm.nih.gov/35783114/
8. Ferrucci, L., et al. (2022). Biological age predictors: The status quo and future trends. https://pmc.ncbi.nlm.nih.gov/articles/PMC11634725/
9. Belsky, D. W., et al. (2021). Clinical biomarkers and associations with healthspan and lifespan. https://pmc.ncbi.nlm.nih.gov/articles/PMC11634725/