It’s common knowledge being depressed takes a toll on your mind and body. But a new study finds depression can cause premature aging.

Telomeres, the protective caps on the ends of chromosomes, naturally shorten over time as we get older, but they’re also vulnerable to outside sources of stress and depression — both of which have been repeatedly linked with the premature shortening of telomeres.

The stress response in humans is regulated by the hypothalamic-pituitary-adrenal axis, or HPA axis. It controls the body’s levels of the stress hormone cortisol, and doesn’t function normally in people with depression and stress-related illnesses.

To study the relationships between telomere length, stress, and depression, scientists measured telomere length in healthy patients and in those with a major depressive disorder. In addition, stress was measured by taking cortisol levels and by administering a questionnaire to study participants.

In work published this week in Biological Psychiatry, researchers not only found that telomere length was shorter in the depressed patients, but that shorter telomere length was associated with low cortisol levels in both the healthy and the depressed individuals.

Study author Dr. Mikael Wikgren said in a press release, “Our findings suggest that stress plays an important role in depression, as telomere length was especially shortened in patients exhibiting an overly sensitive HPA axis. This HPA axis response is something which has been linked to chronic stress and with poor ability to cope with stress.”