Aging clocks may not measure the same thing
Dozens of tests claim to measure your biological age. But are they actually measuring the same thing? A comprehensive review raises serious questions about how interchangeably these clocks are presented.
Biological age is a compelling idea. It suggests that your body can age faster or slower than your calendar age implies. Aging clocks try to quantify this by analyzing patterns in blood markers, DNA methylation, or other measurable features. Machine learning plays a central role: algorithms learn from large datasets which combination of features best predicts chronological age or disease risk.
Three generations of clocks
The review, published in Radiologic Clinics, distinguishes three generations. The first generation was trained to predict calendar age. The second targets disease risk and mortality probability. The third attempts to measure the pace of aging by comparing repeated measurements over time. Each approach measures something different. The researchers emphasize that biological aging likely consists of multiple, partly independent processes, and that no single clock captures all those dimensions at once.
Among the processes clocks try to capture is immunosenescence: the gradual decline of the immune system with age. Another is chronic low-grade inflammation, sometimes called inflammaging, in which the body maintains a persistent mild inflammatory state without active infection. That both contribute to aging is reasonably well established. How they relate to what clocks actually measure is far less clear.
No gold standard yet
A recurring problem is causality. Does someone score higher on an aging clock because they are aging faster, or is it the other way around? The review also points to confounding: clocks are influenced by factors such as smoking, illness, or medication use, which are separate from the aging process itself. Reproducibility is another concern. Findings from one study do not always replicate in a different population.
That does not make aging clocks useless. From a longevity perspective, they are a useful instrument for comparing groups or tracking interventions at the population level. But the review makes clear that translating results to individual clinical practice is still a distant goal. The researchers call for longitudinal studies in diverse populations to improve interpretability.
Want to research this yourself? Try these search terms: DNA methylation aging clocks, immunosenescence biomarkers, inflammaging chronic low-grade inflammation