Scientists are increasingly finding that depression and other psychological disorders can be as much diseases of the body as of the mind.

People with long-term psychological stress, depression and post-traumatic stress disorder tend to develop earlier and more serious forms of physical illnesses that usually hit people in older age, such as stroke, dementia, heart disease and diabetes. Recent research points to what might be happening on the cellular level that could account for this.

Scientists are finding that the same changes to chromosomes that happen as people age can also be found in people experiencing major stress and depression.

The phenomenon, known as "accelerated aging," is beginning to reshape the field's understanding of stress and depression not merely as psychological conditions but as body-wide illnesses in which mood may be just the most obvious symptom.

"As we learn more…we will begin to think less of depression as a 'mental illness' or even a 'brain disease,' but as a systemic illness," says Owen Wolkowitz, a psychiatry professor at the University of California, San Francisco, who along with colleagues has conducted research in the field.