Every time a cell divides, protective tips (telomeres) on the ends of its chromosomes shorten. This causes cell aging. Without these protective coverings, cell divisions are less accurate and are limited in number. In the 1980’s, Dr. Elizabeth H. Blackburn et al discovered telomerase, a protein which allows recovery in telomere lengths.
Now, Dr. Rita Effros and associates at UCLA have shown how stress with its concomitant production of cortisol can increase the rate of aging in immune cells. One of the multiple functions of cortisol is to reduce the production of telomerase and thus cause premature shortening of the telomeres.
A longer summary of this information can be found at http://www.eurekalert.org and the original article, UCLA Study Identifies Mechanism behind Mind-Body Connection, in the May 2008 issue of Brain, Behavior and Immunity.