Telomere attrition or telomere shortening is a hallmark of aging, and refers to the shortening of the telomeres each time the DNA is replicated during cell division. Telomeres are sequences of repetitive DNA that contain no useful genetic information, and can be likened to the plastic tips on shoelaces, protecting the ends of the chromosomes from damage.
After a enough cell divisions (40-60 in humans) telomeres will become too short to adequately protect the genetic code. At this point, cells will usually either stop dividing (this is called replicative senescence) or ‘commit suicide’ (apoptosis). This is essential to protect against damage to the genetic code and the development of cancer. However, telomere attrition contributes to tissue dysfunction in old age as cells are depleted through senescence or apoptosis. A more detailed explanation of telomere attrition can be found in this article.
Telomere shortening during cell division.
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