Review of 435 studies: biological age measures often diverge

Review of 435 studies: biological age measures often diverge

On September 8, Frontiers in Aging published a review covering publications from January 2011 through June 2023. The authors catalogued signs of aging in the body and methods for converting them into age estimates. The resulting map shows that such estimates depend on the signals chosen and on the population in which they were validated.

Chronological age counts years lived. Biological age attempts to capture how aging manifests in the body: for example, through telomere length (the protective caps at chromosome ends), blood proteins, or gene activity. Some estimates rely on a single marker, while others are derived from models that combine multiple signals. As a result, the same term "biological age" can refer to quite different measurements.

The review includes 435 publications. Telomeres offer a clear example: in 123 of 162 studies, participants with higher chronological age tended to have shorter telomeres, while 25 studies found no such statistical association. The association appeared frequently but varied across studies, leaving telomere length as one of the signals of age-related change among several.

Beyond telomeres, the review examines blood proteins and other circulating molecules, gene activity, and composite models that integrate multiple markers. The authors note that different measures of biological age yield different answers and ask how these measurements relate to one another. A separate question concerns the markers themselves: which ones merely respond to aging and which ones actively participate in producing age-related changes in the body. This distinction matters for selecting markers suited to diagnosis and for evaluating the outcomes of interventions.

The population used for validation also matters. In one of the included studies, algorithms performed more accurately on data from the population on which they were trained. The authors also consider differences across sex, ethnic, and socioeconomic groups, as well as the influence of lifestyle and environmental conditions. An age estimate becomes more informative when accompanied by its explanation: what signals it combines, what those signals reflect in the body, and in which population the calculation was validated.