Background: Depression may increase risk for Alzheimer disease (AD), but it is not clear whether this risk is mediated by structural brain changes. We determined whether history of depressive episodes and presence of depressive symptoms were associated with smaller hippocampal and amygdalar volumes and with increased risk for incident AD.
Methods: Within the Rotterdam Scan Study 503 persons, aged 60-90 years at baseline and without dementia, reported their history of depressive episodes. Depressive symptoms were assessed with the Center for Epidemiologic Studies Depression Scale. Volumetric assessment of the hippocampus and amygdala was performed using three-dimensional MRI. All subjects were followed for an average of 6 years for development of AD, diagnosed according to National Institute of Neurological and Communicative Disorders and Stroke-Alzheimer's Disease and Related Disorders Association criteria.
Results: A total of 134 subjects (26.6%) reported a history of depression (88 reported an onset <60 years and 46 a late onset). Multiple linear regression analyses did not reveal a significant association with hippocampal or amygdalar volume for any of the depression parameters. During follow-up, 33 persons developed AD. Cox regression analyses showed that subjects with early onset depression had an increased risk for AD (HR 3.76; 95% CI 1.41 to 10.06), independent of hippocampal and amygdalar volume, whereas this risk was 2.34 (95% CI 0.82 to 6.69) in subjects with a late-onset depression. Depressive symptoms at baseline were not associated with increased risk for AD.
Conclusion: History of depression, and particularly an early onset, but not presence of depressive symptoms increased the risk for Alzheimer disease. This risk was not mediated by smaller hippocampal or amygdalar volumes.