Telomeres and Aging
The observation is that young people have long telomeres and old people have short telomeres. As one might expect however, there can be a substantial difference among individuals. Some older persons have longer end caps than one might expect for their chronological age. This might explain variations in length of life (lifespan) and in quality of life (health span) in humans. Granted that nutrition and physical activity remain at the cornerstone of quantity and quality, but again the gene is a very powerful determinant in outcomes.
Leonard Hayflick, a cellular biologist who calculated the number of cell divisions possible in the ideal (50-70), estimated a maximum life expectancy in humans to be 120 years. In fact, the longest a human has ever been proven to live is 122 years, the case of Jeanne Calment who was born in 1875 and died in 1997. Although her telomeres were not studied, scientists have been able in the laboratory to keep cultured cells dividing beyond their normal years with the use of telomerase (the enzyme that repairs end caps keeping them long). Such experiments, along with the work of Blackburn and Greider who won the Nobel Prize in Medicine in 2009, have given rise to exciting possibilities for “treatment” of aging by the activation of the telomerase enzyme.
Geneticist Richard Cawthon, from the University of Utah, found that when people are divided into two groups based on telomere lengths, the half with longer telomeres lives five years longer than those with shorter telomeres. That suggests lifespan could be increased five years by increasing the length of telomeres in people with shorter ones. Once a person is older than 60, the risk of death doubles every eight years. People with longer telomeres still experience telomere shortening as they age. How many years might be added to our lifespan by completely stopping telomere shortening? Cawthon believes 10 years and perhaps even up to 30 years. Some long-lived species like humans have telomeres that are much shorter than species like mice, which live only a few years. Nobody yet knows why. But it’s evidence that telomeres alone do not dictate lifespan.
Once a person is older than 60, their risk of death doubles with every eight years of age. So a 68-year-old has twice the chance of dying within a year compared with a 60-year-old. Cawthon’s study found that differences in telomere length accounted for only 4 percent of that difference. And while intuition tells us older people have a higher risk of death, only another 6 percent is due purely to chronological age. When telomere length, chronological age and gender are combined (women live longer than men), those factors account for 37 percent of the variation in the risk of dying over age 60. So what causes the other 63 percent?