Biomarkers of aging: do we know what to look for?

The identification of specific biomarkers of aging would be an important milestone in gerontologic research. In this communication, the goals of identifying biomarkers of aging are summarized and some criteria for defining biomarkers are suggested. An age-related alteration in a biological parameter is not necessarily a biomarker of aging. None of the previously observed age-related changes satisfies all the criteria. Potential biomarkers that are applicable to human aging include in vitro proliferative capacity of fibroblasts, glycation of collagen, and DNA unwinding rate. Future research should focus on identifying age-related changes that are not merely expressions of aging, but also have some causal link to aging.