Between-person and within-person effects in the temporal relationship between depressive symptoms and cognitive...

We aimed to disentangle within-person and between-person effects in the temporal relationship between depressive symptoms and cognitive function.

We performed a prospective population-based cohort study on participants of the Survey of Health, Ageing and Retirement in Europe. Cognitive function was assessed by tests on verbal fluency, immediate recall and delayed recall. Depressive symptoms were measured with EURO-D scale. To determine the temporal order of the association between cognitive function and depressive symptoms, we employed the fully saturated cross-lagged panel model (between-person effects), and random intercept cross-lagged panel model (within-person effects).

In 59,311 participants (mean age 65, ranging 46-100), between-person effects showed a bi-directional relationship that could be seen in three stages: First, the effect of cognitive function on depressive symptoms was initially slightly stronger than vice versa. Second, the effect of depressive symptoms on cognitive function became stronger during the follow-up. Third, all effects were small and no direction dominated. Within-person effects, however, revealed a dominant effect from depressive symptoms on cognitive function. Some effects from cognitive function on depressive symptoms were apparent only in older adults, in particular men. All effects were small and strongest for individuals aged 65 years and above.

The sample is healthier than general population and thus not fully representative. A comprehensive cognitive battery was not available.

Long-term relationship between depressive symptoms and cognitive function is bi-directional. However, to achieve improvement in an individual in the short-term, the focus should be on decreasing depressive symptoms to improve cognitive function.