Chronic stress seems to trigger the premature aging of immune system cells, a new study suggests. Although people who are under stress for long periods often look haggard, scientists don’t understand how chronic stress causes damage at the cellular level.

The new research focused on one sign of biological aging – caps of DNA and protein at the end of chromosomes called telomeres, which shorten as cells reproduce over time. Young people have an enzyme that regenerates the ends, but this process stops late in life.

• Dr. Elissa Epel, Assistant Professor, Department of Psychiatry at the University of California, San Francisco and Director of Research, Center for Obesity Assessment, Study & Treatment