More than 650 elderly people took part in the seven-year study which included annual neurological evaluations and testing of cognitive function. Baseline testing showed about half of the participants had no depressive symptoms and the remainder had from one to eight. Only 1 percent had symptoms severe enough to warrant a diagnosis of major depression.
During annual follow-ups, 108 of 651 participants developed Alzheimer's disease. Those with the greatest number of depressive symptoms at the start of the study were more likely to develop Alzheimer's disease and also showed more rapid cognitive decline.
"According to our results, the people with the largest number of depressive symptoms also had the greatest risk of developing AD," according to lead author Robert S. Wilson, PhD, of the Rush Alzheimer's Disease Center in Chicago, IL. "With each additional symptom, the risk of AD increased by about 20 percent."
Study participants are from the Religious Orders Study, an on-going look at aging and Alzheimer's disease in older Catholic nuns, priests, and brothers who have agreed to annual evaluations and brain donation at death. Participants were all over age 65, and did not have dementia at the time of enrollment. "We are grateful for the remarkable dedication and altruism of this unique group of people," said Wilson.
The National Institute on Aging supported the study.
The American Academy of Neurology, an association of 18,000 neurologists and neuroscience professionals, is dedicated to improving patient care through education and research. For more information about the American Academy of Neurology, visit its web site at www.aan.com. A related article on Alzheimer's disease for patients can be found on the Neurology web site at www.neurology.org.