Depression can kill old people, just like heart disease and other illnesses that receive a lot more attention in that regard.

An analysis by researchers at the University of Pittsburgh, University of Pennsylvania and Cornell University found a group of individuals 60 and over diagnosed with depression were nearly twice as likely to die as people lacking that diagnosis.

They had no ready explanation for the difference, just knew it existed among 1,226 randomly selected visitors to doctor's offices they studied over a two-year period. Few of the deaths among them could be directly connected to the depression by acts of suicide.

It appeared to play a factor, however, in their deaths from physical problems such as cardiovascular ailments, the researchers wrote in an article just published in the September issue of the American Journal of Geriatric Psychiatry.

"How depression increases death rates is not clear," said Dr. Joseph Gallo, the lead researcher, from the University of Pennsylvania's School of Medicine. "Possibly depression makes people less likely to take care of themselves, or acts directly on the immune system in ways we do not completely understand."

One third of those studied were from the Pittsburgh area. They were part of an original collaboration among the three universities that found reduced depression in patients if they were closely monitored by a case manager, as opposed to being left to the care of their general practitioner. These primary care physicians tend to be more focused on physical ailments than on exploring mental health issues such as depression, the researchers say.

The look at mortality rates analyzed the same individuals, especially the 64 who died during the two-year study period. The research took into account the fact that people with other health issues, such as diabetes or heart disease, might be more likely to be depressed than the average person.

Those suffering from depression were still nearly twice as likely to die as others with the same illnesses who were fine mentally.

"We estimated that about one in 10 deaths would be prevented if the influence of depression could be eliminated from the population from which our sample was drawn," the researchers wrote.

Dr. Edward Post, a Pitt assistant professor of medicine and psychiatry who was part of the team, said the findings will be examined further to look for any difference in death rates among those who received special treatment for depression, and those who did not.

"In terms of thinking about threats to your life, we found depression on a similar par to diabetes and coronary heart disease," Post said. "Clearly, depression can make people less able to function, less likely to be compliant with medication, to have functional impairments. ... This should really help people focus on the seriousness of depression, to put it on a par with these other illnesses that are clearly seen to cause a lot of other problems and functional mortality."