Studies on biomarkers of aging have looked for changes in cells, hormones, genes, and even behaviors to find a predictor of the rate of aging.

One target that has been looked at is the central nervous system (consisting of the brain and spinal cord). Computerized tomography (CT) scans can be used to look for changes in the brain that may serve as biomarkers of aging. For example, the brain shrinks with age. This does not mean that brain cells necessarily die, but rather they become smaller in size and volume. Some research has been done to find out if brain shrinkage in certain areas may underlie the changes in function that occur with age. So far, brain function and age have proved too complex to produce reliable biomarkers.

Age at menopause has been suggested as a possible biomarker of aging for women. One study showed that women who had early menopause (before age 44) had shorter life spans than women who experienced menopause at ages 50 to 54. This suggests that the ovaries play a role in directing the overall aging process. But this requires further study.

At the level of cells, a potential biomarker of aging is length of telomeres. Within each cell, there are chromosomes, and at the ends of each chromosome are telomeres. Each time a cell divides, telomeres become shorter. After a certain number of cell divisions, the telomeres become too short to allow the cell to continue to divide, at which point the cell dies. Therefore, cells have a limited life span. One proposed biomarker of aging would be a test to detect telomere length.

However, the telomere story is complicated. For example, an enzyme called telomerase helps to keep telomeres from becoming too short. And the effect of telomere length and aging differs in different parts of the body, so, like other possible biomarkers discusses, telomeres' exact relationship to the body or organism's life span bears further inquiry.