Genetics and lifestyle are fundamental factors that affect telomere length and the rate at which they shorten. Certain life habits have been significantly associated with having longer or shorter telomeres.
Cells stop duplicating when telomeres become too short. Therefore telomere length is considered to be an excellent biomarker of tissue renewal capacity and, consequently, of organismal aging.
Telomerase is an enzyme which is able to elongate telomeres and repair short telomeres by re-elongating them. To this end, telomerase adds telomeric repeats to the chromosome ends. In non-pathological conditions telomerase is expressed in early stages of embryo development as well as in certain adult stem cell compartments.