The April 8 issue of Neurology carries the results of a study conducted on 486 people ranging in age from 60 to 90 with no symptoms of dementia. These same people were monitored for about six years each to see if anyone developed Alzheimer’s disease.

Earlier bouts of depression were logged, too, with 134 study participants reporting at least one depressive episode that required medical intervention. Some of the participants reported feelings of depression at the onset of the study but others did not.

During the follow-up period, 33 participants developed Alzheimer’s disease, with participants reporting earlier episodes of depression being 2.5 times more likely to develop the disease than participants who had never been clinically depressed. The risk increased, up to 4 times, for participants suffering depression before turning 60 years old. Participants reporting depressive symptoms at the beginning of the study were no more or less likely to develop Alzheimer’s than those not depressed.

Lead author for the study, Monique M. B. Breteler, MD, PhD, Erasmus University Medical Center, Rotterdam, the Netherlands, calls for more studies to determine the exact nature of the connection between depression and dementia. Yet to be determined is if depression causes Alzheimer’s to develop or if something entirely different causes both diseases.

One theory under review is a possible connection between the loss of cells in the hippocampus and the amygdala that occur with depression and the development of Alzheimer’s disease later in life. Scans of these two areas of the brains of the study participants, however, revealed no significant differences between the group reporting earlier depressive episodes and those who had never experienced depression.

The Netherlands Organization for Scientific Research and the Health Research and Development Council funded this study.