Psychiatrists and researchers at the University of Rochester Medical Centre said that this was the first study to assess simultaneously the roles of depression and intellectual dysfunction over time in a large group of older people.
"We can't conclude that treatment or prevention of depression would reduce or prevent cognitive decline but these findings certainly raise the possibility and that would be our hope," Jeffrey M. Lyness, M.D., professor of psychiatry, associate chair for education in the Department of Psychiatry and senior author of an article on the research said.
In the study, more than 700 patients were examined for two years. The researchers analysed executive functions that involved high-level mental processes, such a making decisions, organizing, planning and doing a series of things in sequence.
"You can have a good memory and good language skills but if you lose executive function, you can't do very well in daily life," Lyness said.
The patients were questioned by trained interviewers, who reviewed each patient's primary care medical chart, recording information about mood and cognitive symptoms, disorders, or treatments as well as active and past medical problems and current medications.
Interviews included assessments of cognition, functional status, and depression. Additional interviews and chart reviews were conducted a year later after the initial interview and then again two years later.
"Not every elderly person who is depressed becomes intellectually impaired, but depression raises the risk of executive dysfunction. We began to see it at the one-year mark and it was clear after two years," Lyness said.
The researchers concluded that physicians treating older patients should be aware of the increased risk of loss of mental functions for depressed patients.
The study is published in The American Journal of Psychiatry.