What does your ‘biological age’ actually mean? Scientists take a closer look

Published on 17/08/2026 - 7:00 GMT+2 Two people can be the same age on paper but very different health-wise. ADVERTISEMENT ADVERTISEMENT Scientists already use several established methods to estimate how quickly a person is ageing biologically. Now, a new study has looked at what is happening inside the body when five of the most widely used methods signal faster ageing. What is an epigenetic clock? The methods, known as epigenetic clocks, are mathematical models based on DNA methylation – chemical changes around DNA that can affect how genes behave without changing the genetic code itself. Epigenetic clocks are widely used in ageing research to study how biological ageing relates to disease, physical decline and the risk of death. “Aging isn’t just about the number of candles on your birthday cake — it’s also about what’s happening inside your cells,” T. Em Arpawong, a research associate professor of gerontology at the USC Leonard Davis School, said in a press release. But it wasn’t yet known what was happening inside the body when each clock indicated faster ageing. To investigate this, researchers in the United States analysed blood samples from 3,227 people in the US Health and Retirement Study. They compared five commonly used epigenetic clocks with gene activity in the blood samples to see what was happening in the body when each clock indicated faster ageing. The study found that the five clocks were associated with different signs of ageing in the body. Some were more closely linked to how the body uses energy and how cells grow, while others were associated with immune activity and inflammation. The clocks also shared some common features, particularly changes involving the immune system, metabolism and communication between cells. Opening the ‘black box’ of biological ageing clocks Researchers say the findings could help scientists choose which ageing clock is most useful for a particular study. One may, for example, be better suited to research on the immune system, while another may be more useful for studying metabolism. The team also developed new measurements called transcriptomic ageing gene scores (TAGS) based on the study findings. In several cases, TAGS were better than the clocks alone at predicting frailty, walking speed, heart disease, diabetes, lung disease and mortality, according to the study. Senior author Eileen Crimmins at the USC Leonard Davis said the work helps open up the “black box” behind biological ageing clocks by showing which molecular processes are associated with their readings. “By uncovering the molecular programs behind these biomarkers, our findings improve their interpretability and help guide their use in geroscience, epidemiology, and future clinical applications,” she said.