Treating depression in older adults may be a life-saving intervention, a new study suggests.

It has been known for some time that depressed people are more likely to die, but it has never been clear that treating their depression would help extend their lives.

Researchers studied 1,226 patients over 60 in the care of general practice doctors; of those, 599 met the diagnostic criteria for either major depression or clinically significant minor depression. The researchers randomly assigned about half the patients to a depression treatment program within the general practice that included psychotherapy and drugs. The study was published in the May 15 issue of The Annals of Internal Medicine.

The scientists found no difference in the survival of people with minor depression in the treated or untreated groups. But after controlling for age, sex, smoking status, education level and current physical illnesses, people with major depression who were treated were about half as likely to die during a five-year follow-up as those who were left untreated. For reasons that are unclear, the reduction in deaths seemed to come almost entirely in the group of patients who had cancer.

The authors acknowledge that they cannot rule out the possibility that the reduction in deaths was caused by some factor other than the treatment for depression, and they also recognize that errors in diagnosis could have affected their results.

Still, said Dr. Joseph J. Gallo, the lead author and an associate professor of family practice at the University of Pennsylvania, “This shows that for people who meet the criteria for major depression, it’s important to get treatment, whether it’s psychotherapy or medication, and a place to begin can be with one’s own doctor.”