Recurrent depressive symptoms and the incidence of dementia and mild cognitive impairment

Abstract

Objective: A history of depression has been linked to an increased dementia risk. This risk may be particularly high in recurrent depression due to repeated brain insult. We investigated whether there is a dose-dependent relationship between the number of episodes of elevated depressive symptoms (EDS) and the risk for mild cognitive impairment (MCI) and dementia.

Methods: A total of 1,239 older adults from the Baltimore Longitudinal Study of Aging were followed for a median of 24.7 years. Diagnoses of MCI and dementia were made based on prospective data. Participants completed the Center for Epidemiologic Studies Depression Scale at 1- to 2-year intervals and were considered to have an EDS if their score was > or = 16. Kaplan-Meier survival curves, log-rank test for trend for survivor functions, and Cox proportional hazards models were conducted to examine the risk of MCI and dementia by number of EDS.

Results: We observed a monotonic increase in risk for all-cause dementia and Alzheimer disease as a function of the number of EDS. Each episode was associated with a 14% increase in risk for all-cause dementia. Having 1 EDS conferred an 87%-92% increase in dementia risk, while having 2 or more episodes nearly doubled the risk. Recurrence of EDS did not increase the risk of incident MCI.

Conclusions: Our findings support the hypothesis that depression is a risk factor for dementia and suggest that recurrent depression is particularly pernicious. Preventing the recurrence of depression in older adults may prevent or delay the onset of dementia.

Figure 1 Kaplan-Meier survival curve of time to incidence of dementia by recurrence of depressive symptoms (DS) Results are based on Cox proportional hazards model and log-rank test for trend. Recurrence of DS was based on the number of visits in which the Center for Epidemiologic Studies Depression Scale (CES-D) score was ≥16. The variable was time-dependent so that a person can be without a history of elevated DS in 1 period of time, screening positive once in another, and twice or more in a subsequent period of time, in a cumulative fashion. However, visits with missing CES-D scores were considered as missing for the time-dependent variable. This analysis was based on 142 failures.

Figure 2 Kaplan-Meier survival curve of time to incidence of mild cognitive impairment (MCI) by recurrence of depressive symptoms (DS) Results are based on Cox proportional hazards model and log-rank test for trend. Recurrence of DS was based on the number of visits in which the Center for Epidemiologic Studies Depression Scale (CES-D) score was ≥16. The variable was time-dependent so that a person can be without a history of elevated DS in 1 period of time, screening positive once in another, and twice or more in a subsequent period of time, in a cumulative fashion. However, visits with missing CES-D scores were considered as missing for the time-dependent variable. This analysis was based on 86 failures.