The researchers have found that the stress hormone cortisol suppresses immune cells' ability to activate their telomerase, enzymes that keep the cells young by preserving their ability to continue dividing.

They point out that every cell contains a tiny clock called a telomere, which shortens each time the cell divides.

According to them, short telomeres are linked to a range of human diseases, including HIV, osteoporosis, heart disease and aging.

Previous studies, says the research team, have shown that telomerase keeps immune cells young by preserving their telomere length.

The researchers insist that their latest study may help understand why the cells of persons under chronic stress have shorter telomeres.

The findings shed new light on how stress makes people more susceptible to illness, and also suggest a potential drug target for preventing damage to the immune systems of persons who are under long-term stress.

A research article describing the study says that this advancement offers new hope for caregivers to chronically ill family members, astronauts, soldiers, air traffic controllers, and people who drive long daily commutes.

"When the body is under stress, it boosts production of cortisol to support a "fight or flight" response," says Rita Effros, professor of pathology and laboratory medicine at the David Geffen School of Medicine at UCLA, and a member of the Jonsson Cancer Center, Molecular Biology Institute and UCLA AIDS Institute.