One of the important markers to be considered the human body’s molecular clock, is the length of our telomeres. From the Greek, telos, meaning & “end,” and mere, meaning & “part,” telomeres are the caps on the ends of each of our chromosomes that protect them from being mistaken for damaged DNA. They are composed of thousands of repetitions of the same sequence of 6 base pairs (the letters of DNA). With each cell division, they shorten by about 50-100 base pairs. At young adulthood, the mean lymphocyte telomere length (MTL) is about 8 kb (8,000 kilo base pairs). Once it reaches 4 kb, the cell no longer is able to divide and enters what is called “replicative senescence,” in which it fails to perform its function and produces detrimental inflammatory molecules. The molecular clock stops ticking.

Lymphocytes, is the cell type whose telomere length has been most studied. This is mostly because of its easy access through a routine blood draw, in contrast to a biopsy of, for example, your lungs or arteries. Hundreds of studies have linked the shortening of lymphocyte MTL not only to the aging process, but also to cardiovascular disease, smoking, various cancers, and even psychological stress. (A few studies have measured the correlations between MTL and the telomere lengths of other tissues in the body and have found general agreement.)

The average person’s lymphocyte MTL decreases about 30-50 base pairs per year; you are more likely to be in the higher end of this range if you smoke, don’t exercise, have a lot of stress, or have a chronic disease. If you start out with a lymphocyte MTL of 8 kb and lose 0.04 kb/yr , you will get to the critical length of 4 kb in 66 years, again, very close to the average human lifespan.

Telomere testing is achieved with a simple blood test.