Biological and functional definition of the older patient: the role of biomarkers of aging.

The rate of aging is not uniform among all individuals. Thus, determination of the biological age of an individual and possibly the biological age of his or her organ systems poses a special challenge to the gerontologist. This could be accomplished if specific biomarkers of aging were available, which would allow standardization of studies, help us understand the various determinants of aging, monitor the impact of various interventions on the rate of aging, and possible allow estimates of life expectancy and predictions of future morbidity. Specific criteria need to be developed for accepting a parameter as a biomarker of aging, since an age-related alteration in a biological parameter does not necessarily qualify. Potential biomarkers of human aging include in vitro proliferative capacity of fibroblasts, glycation of collagen, and DNA unwinding rate.