A biomarker of aging is a a way to measure biological age, the burden of cell and tissue damage and consequent dysfunction. A biomarker that permitted the robust, quick, and cheap assessment of biological age would greatly speed up development of rejuvenation therapies. It would allow for rapid and cost-effective tests of many interventions, and the best interventions would quickly rise to prominence. At present the rigorous assessment of ways to intervene in the aging process is slow and expensive, as there is little alternative but to run life span studies. Even in mice that is prohibitively costly in time and funds for most research and development programs.

One of the more severe consequences of this state of affairs is that it takes a long time and sizable expense to weed out the less effective approaches to treatment. That this is a problem is well recognized by the scientific community, and many varied biomarkers of aging are presently under development. Perhaps the best known are the various forms of epigenetic clock, weighted algorithmic combinations of the status of DNA methylation sites that correlate with age and mortality risk. There are other approaches, though, such as combining simple measures of decline such as grip strength or inflammatory markers in blood tests. That class of methodology is explored in today's open access paper, with the focus specifically on measures adopted by the clinical community to assess frailty.

One of the concerns with the epigenetic clock, and for similar efforts using levels of blood proteins, is that it is quite unclear as to what exactly is being measured. The relationship with age and mortality emerges from the data, and it is then up to the research community to establish mechanistic connections between specific epigenetic changes and underlying processes of aging. It is quite possible that these biomarkers do not reflect all of the mechanisms of aging, and thus any use of them to assess a specific approach to rejuvenation would have to be carefully validated in parallel with the development of that therapy. This somewhat defeats the point of the exercise. When building a biomarker based on frailty indices, as here, there is at least a greater degree of confidence that it comprehensively touches on all of the contributions to aging, and we would thus expect any viable rejuvenation therapy to make a difference to the measure of age.

Age and life expectancy clocks based on machine learning analysis of mouse frailty