For over 15 years, the National Institute on Aging has supported research on biomarkers of aging. While many important findings have developed, no biomarker has yet been identified. This is at least partly because of some of the difficulties inherent in the concept of biomarkers.

One difficulty has to do with the overlap between aging and disease. Both the aging process and diseases can cause changes in the body, which affect life span. The idea of biomarkers is to measure the aging process, but it has been difficult to separate this out from the effects of a disease if one is present.

Another obstacle is the fact that some age-related changes cause no harm, while others does. It isn't entirely known which changes are harmful and which are benign. This makes it more difficult to pinpoint exactly what to look for.