Dual Trajectories of Depression and Cognition: A Longitudinal Population-Based Study.

OBJECTIVE: To examine the relationships over time between dual trajectories of depressive symptoms and several cognitive domains.
METHODS: In a 5-year longitudinal study, 1,978 randomly selected individuals aged 65+ years at recruitment were assessed annually. Repeated measures were of depressive symptoms on the modified Center for Epidemiologic Studies Depression Scale and composite scores in the cognitive domains of attention, executive function, memory, language, and visuospatial function. Latent class trajectories were identified for depression and for each cognitive domain and their associations investigated using dual trajectory modeling. Cognitive trajectories with z scores below -1 were designated as persistently low.
RESULTS: Five depressive symptom trajectories were observed: rarely depressed (60.5%); low-grade, decreasing symptoms (18.5%); low-grade, increasing symptoms (9.6%); moderate-grade symptoms (7.4%); and consistent higher-grade symptoms (4.0%). For each cognitive domain six trajectories were observed. The rarely depressed and low-grade decreasing symptom groups were the least likely to have persistently low cognition. The symptom trajectory most strongly associated with persistently low functioning in each domain was not the higher-grade group but rather the low-grade increasing group in the case of attention and the moderate-grade trajectory in the other four domains.
CONCLUSION: Consistently higher-grade depressive symptoms are less strongly associated with poor cognitive functioning than with either moderate- or low-grade increasing depressive symptom trajectories, over time and across different domains. Examining both depression and cognition longitudinally allows heterogeneity of both to be addressed, revealing latent groups with potential diagnostic and prognostic implications.