Depression and cognition: how do they interrelate in old age?

Objectives: To disentangle the reciprocal effects between depressive symptoms and cognitive functioning over time and to study the association between changes in their trajectories using 13 years of follow-up.

Design and participants: Data were used from five waves of the population-based Longitudinal Aging Study Amsterdam. Subjects were included if data was present on depressive symptoms and cognitive performance on at least two occasions, which resulted in a study sample of N = 2,299.

Measurements: Depressive symptoms were assessed with the Center for Epidemiologic Studies Depression Scale. Cognitive functioning was assessed using the Mini-Mental State Examination (general cognitive functioning) and timed coding task (speed of information processing).

Results: Cross-domain latent change analyses showed that depression at baseline predicted both decline of general cognitive functioning and information processing speed, independent of relevant covariates. Conversely, information processing speed at baseline, but not general cognitive functioning was related to the course of depressive symptoms. The course of cognitive functioning was not significantly associated with the course of depressive symptoms.

Conclusion: Depressive symptoms in older patients flag an increased likelihood of cognitive decline. This effect is considerable and may be due to several underlying mechanisms. The likelihood of the relationship reflecting either a causal effect of depression on cognitive decline, or a common cause, or both, should be estimated. Likewise, older persons with more limitations in information processing speed specifically are more vulnerable to increases in depression.