In older adults, major depression might be a "treatable risk factor" for Alzheimer's disease, write the researchers. They included Michael Rapp, MD, PhD, of New York's Mount Sinai School of Medicine.
The study appears in the Archives of General Psychiatry.
Depression is common -- and often treatable -- in people of all ages.
"Some people have the mistaken idea that it is normal for the elderly to feel depressed," states the NIMH's web site. "On the contrary, most older people feel satisfied with their lives."
"Improved recognition and treatment of depression in late life will make those years more enjoyable and fulfilling for the depressed elderly person, the family, and caretakers," the NIMH states.
The seniors in Rapp's study had spent their last years in a nursing home in the Bronx section of New York City. They had all been diagnosed with probable or possible Alzheimer's disease.
Until they died -- up to eight years after diagnosis with probable or possible Alzheimer's -- the patients took yearly tests of their mental skills. Their medical records were also checked for any history of major depression.
The patients were about 80 years old, on average, when they died. Afterwards, Rapp's team studied the deceased patients' brains, with the consent of the patients' families.
Slightly less than half of the patients (44%) had a lifetime history of major depression. Other studies have shown as many as 30% to 50% of people with Alzheimer's disease have major depression, write Rapp and colleagues.
Faster Alzheimer's Decline
Compared with patients with no depression history, those with a lifetime history of major depression had:
- Faster cognitive decline
- More brain plaque and tangles associated with Alzheimer's disease
For instance, cognitive test scores dropped about 1.15 points annually for patients with no history of major depression, compared with a yearly drop of about 1.86 points for those with a history of major depression.
Patients who had a lifetime history of major depression and Alzheimer's had more plaque and tangles in their brains.
Other studies have also shown a greater risk of Alzheimer's for people with a recurrent history of geriatric depression, write Rapp and colleagues. Taming seniors' depression might help slow or prevent Alzheimer's disease, they note, cautioning that their study doesn't prove that.
Older adults with and without depression should be studied further to see if depression truly worsens Alzheimer's and how that process works, the researchers write.