The Problem with Biomarkers of Aging
Today's research materials illustrate the primary challenge faced by those who want to develop and use biomarkers of aging, ways to measure biological age rather than chronological age. All reasonable biomarkers of aging are actually useful and informative when it comes to unmodified aging. This is true of everything from combinations of simple tests, such as walking speed and grip strength, through to more modern contrivances based on machine learning techniques applied to epigenetic, transcriptomic, proteomic, or other voluminous data on the state of our biology that can be easily produced these days. One can see clear correlations between these biomarkers and mortality, and between these biomarkers and state of health in later life.
The problem arises once we start considering the effective treatment of aging as a medical condition. Not aging as a whole, of course, because aging is a set of diverse processes and their consequences that are very different from one another, and require very different strategies in order to build meaningful therapies. When testing a rejuvenation therapy that repairs one form of damage, or reverses one process of the many processes of aging, how will that treatment affect measures of aging? The answer probably differs on a case by case basis, and at present, despite the existence of at least one approach to rejuvenation that has actual, working therapies, meaning the clearance of senescent cells via senolytic treatments, there is no map to connect treatment to effect on biomarkers.
In practice, this means that biomarkers can't be trusted as tools to evaluate whether or not potential rejuvenation therapies are actually any good, at least until after researchers have run many life span studies using both those therapies and those biomarkers in order to produce a calibration. That will take a good deal of time and effort, and makes biomarkers for aging a very much less useful than hoped at the present time.
Biomarkers used to track benefits of anti-ageing therapies can be misleading