Another day, another clock…

We have seen several new biological age clocks published in the last couple of years and this latest from the Buck Institute for Research on Aging is an excellent addition (https://www.nature.com/articles/s43587-025-00883-5?trk=public_post_comment-text#author-information). But despite the hype and celebrity endorsements, are these clocks actually clinically useful?

The measurement problem…

Researching aging in humans is difficult because it is hard to measure. If we were to truly assess whether an intervention actually prolonged lifespan we would need to run trials lasting decades and with a sample size big enough to control for the rates of preventable disease and misadventures. This would not only be prohibitively expensive but unethical. What we need is a way to measure the rate of aging, which is the hope for biological age clocks.

The definition problem…

To measure something you need to define it and with aging this is surprisingly difficult. The concept of biological age describes the fact that people of the same chronological age can appear to be physiologically different ages. How can we systematically compare biological ages?

One approach used by many clocks is to predict an individual's risk of all-cause mortality from a set of parameters (like blood tests). This is based on the concept of “Gompertz age” which essentially describes the fact that our risk of dying increases as we get older. Theoretically, people with a higher biological age have a higher mortality risk.

The new clock presented by the Buck institute uses a different definition of aging called “Intrinsic Capacity” which is a composite of various physiological and cognitive measures which are known to decline with age. Where Gompertz age clocks predict lifespan, this clock aims to predict healthspan.

Are they useful?

Despite their popularity, biological age clocks are not particularly useful on an individual basis. Not only do results vary significantly between clocks, but the information they give us isn’t particularly actionable. A panel of well understood biomarkers like body composition, VO2 max, and blood lipid levels will give much more useful insights into how you can live healthier. Currently biological age clocks are at best interesting conversation starters.

So what is the future?

Biological age clocks are an exciting innovation for medical science. Being able to directly measure the rate of aging could greatly speed up the pace at which we can test new treatments. However, science doesn’t always move as fast as we want it to and there is a lot of work left to do before we have a standardised test for biological age. In the meantime we will follow the story while using the best available clinical information to support our clients in their health journeys.

By Dr Robin Brown