Is insomnia a perpetuating factor for late-life depression in the IMPACT cohort?

Abstract

Study objectives: Insomnia and depressive disorders are significant health problems in the elderly. Persistent insomnia is a risk factor for the development of new-onset and recurrent major depressive disorder (MDD). Less clear is whether persistent insomnia may perpetuate MDD andlor dysthymia. The present longitudinal study examines the relationship of insomnia to the continuation of depression in the context of an intervention study in elderly subjects.

Design: Data were drawn from Project IMPACT, a multisite intervention study, which enrolled 1801 elderly patients with MDD and/or dysthymia. In the current study, subjects were assigned to an insomnia-status group (Persistent, Intermediate, and No Insomnia) based on insomnia scores at both baseline and 3-month time points. Logistic regressions were conducted to determine whether Persistent Insomnia was prospectively associated with increased risk of remaining depressed and/or achieving a less than 50% clinical improvement at 6 and at 12 months compared with the No Insomnia reference group. The Intermediate Insomnia group was compared with the other 2 groups to determine whether a dose-response relationship existed between insomnia type and subsequent depression.

Setting: Eighteen primary clinics in 5 states.

Participants: Older adults (60+) with depression.

Measurements and results: Overall, patients with persistent insomnia were 1.8 to 3.5 times more likely to remain depressed, compared with patients with no insomnia. The findings were more robust in patients receiving usual care for depression than in patients receiving enhanced care. Findings were also more robust in subjects who had MDD as opposed to those with dysthymia alone.

Conclusions: These findings suggest that, in addition to being a risk factor for a depressive episode, persistent insomnia may serve to perpetuate the illness in some elderly patients and especially in those receiving standard care for depression in primary care settings. Enhanced depression care may partially mitigate the perpetuating effects of insomnia on depression.

Figure 1

Dose-Response Relationship of Insomnia Status Across Depression Outcomes. The Persistent Insomnia, Intermediate Insomnia and No Insomnia groups are represented by the black, grey, and white bars, respectively. The measures of depression are defined as: SCID MDD (Structured Clinical Interview for DSM-III-R diagnosis of major depressive disorder at 6 months); 6 Mo SCL (scoring above the depression cutoff on the 17-item version of the Hopkins Symptom Checklist [HSCL] at 6 months); < 50% at 6 Mo (a less than 50% improvement on the 17-item version of the HSCL from baseline to 6 months); 12 Mo SCL (scoring above the depression cutoff on the 17-item version of the HSCL at 12 months); and < 50% at 12 Mo (a less than 50% improvement on the 17-item version of the HSCL from baseline to 6 months). For each measure of depression, χ² analyses conducted where * denotes P < 0.05 and ** denotes P < 0.001.

Figure 2a

Mean Symptom Score at Baseline. Mean symptom cluster scores of the parent sample (n = 1801) at baseline with a possible range of 0 to 4.0.

Figure 2b

Prevalence of Persistent Symptom. Percentage of the parent sample that exhibited an elevated symptom score at both baseline and the 3-month time point.

Figure 2c

Co-occurring Persistent Symptoms. For each individual symptom, the bar represents the mean number of other persistent symptoms that are co-occurring. For example, subjects with persistent insomnia had a mean of 1.9 co-occurring persistent depressive symptoms.