Background: The relationship between depression and dementia is complex and appreciation of its true nature is evolving. Depression is an early symptom of dementia. Recent research suggests that mood disorders, in general, may be risk factors for the development of dementia.
Method: This was a cross-sectional study of the effect of aging on cognition in patients with mood disorders compared to normal controls. Patients and controls were tested with a comprehensive neurocognitive test battery, CNS Vital Signs. The question at issue was the rate of aging-related cognitive decline the same or different in mood disorder patients compared to normal controls.
Subjects: 455 patients with mood disorders, 336 with major depression and 119 with bipolar affective disorder, age 18-86, and 1003 normal controls, age 35-90. Normal controls were age 18 or older in the CNS Vital Signs normative database. The normal subjects were healthy, on no centrally-active medication, and free of psychiatric and neurological disorders.
Results: Cognitive performance in the two groups run in parallel from age 18 to 45; they begin to diverge during the next decade; after age 65, mood disorder patients, as a group, decline more sharply than normal controls. The differential rate of decline was seen in the domains of memory, attention, processing speed and executive function.
Conclusions: There seems to be an acceleration in age-related cognitive decline in patients with depression in particular, and mood disorders in general, compared to age-matched normal controls. It is likely, then, that as people age, the ones who develop depression, or who fail to recover from early episodes of depression, include a substantial number of patients at risk for developing dementia. This is consistent with the fact that late-life depression may be an early manifestation of dementia. The data are also consistent with the idea that mood disorders are a risk factor, albeit a weak one, for the development of dementia. From a slightly different perspective, one might imagine that some pathophysiological event is shared by the mood disorders and dementing conditions.