Elsevier

Sleep Medicine Reviews

Volume 43, February 2019, Pages 96-105
Sleep Medicine Reviews

Clinical Review
Insomnia as a predictor of mental disorders: A systematic review and meta-analysis

https://doi.org/10.1016/j.smrv.2018.10.006Get rights and content

Summary

Previous research has identified insomnia as a predictor for the onset of depression. The aim of this meta-analysis is to investigate whether insomnia also predicts the onset of other mental disorders. Longitudinal studies were eligible for inclusion if they investigated insomnia at baseline (including nighttime- and daytime-symptoms) as a predictor of the later onset of psychopathology within a follow-up time-frame of at least 12 mo. Thirteen primary studies were included. The results suggest that insomnia is a significant predictor for the onset of depression (10 studies, OR 2.83, CI 1.55–5.17), anxiety (six studies, OR 3.23, CI 1.52–6.85), alcohol abuse (two studies, OR 1.35, CI 1.08–1.67, and psychosis (one study, OR 1.28, CI 1.03–1.59). The overall risk of bias in the primary studies was moderate. This meta-analysis provides evidence that insomnia increases the risk for psychopathology. A future research agenda should include more prospective studies using established diagnostic criteria, assessing insomnia at baseline and including long-term follow-up intervals evaluating a wider range of mental disorders. In addition, prospective long-term interventional studies investigating the efficacy of insomnia treatment for the prevention of mental disorders are called for.

Introduction

With a lifetime prevalence of around 25% of the overall population, mental disorders are highly prevalent [1]. Patients with mental disorders suffer from substantial impairments of quality of life and reduced ability to participate in professional and social life [2]. Around 35–50% of patients with serious mental illness do not receive treatment in developed countries [3]. After onset of a mental disorder, there is often a delay of several years until first treatment is initiated [4]. In addition, among those who receive treatment, rates of nonresponse and relapse are relatively high: for major depression, for example, relapse rates after cognitive behavior therapy or antidepressant medication are around 50% [5], [6].

For economic and practical reasons, it seems reasonable to implement preventive strategies predominantly in those at elevated risk for the onset of a mental disorder. Insomnia, a syndrome characterized by chronic sleep onset and/or sleep continuity problems associated with impairment of daytime functioning, has the potential to serve as an indicator for an elevated risk. Pathophysiologically, insomnia is associated with cognitive and physiological hyperarousal ∗[7], [8] increased pre-occupation with sleep [9] and maladaptive sleep-related behavior [10]. Insomnia has been identified as a predictor for the de-novo onset of major depression in two meta-analyses ∗[11], [12]. The effect sizes (odds ratios) found in these two meta analyses were 2.60 (95% CI: 1.98–3.42) and 2.27 (95% CI: 1.89–2.71). However, in these previous meta-analyses, some primary studies included participants with only nighttime symptoms without daytime symptoms, though daytime symptoms are a necessary requirement for the diagnosis of insomnia disorder. This is a limitation since in clinical practice, nighttime symptoms such as difficulties initiating and maintaining sleep are commonly reported, but do not require medical or psychological interventions in the absence of any daytime impairment. Clinical insomnia with daytime impairment, in contrast, is treated with either pharmacotherapy or psychotherapy [13]. Insomnia is also a frequent symptom of almost all mental disorders [14]. Several studies indicate that insomnia may also be a risk factor for other psychiatric symptoms beyond depression, including anxiety and suicide [15].

This opens up the possibility to use treatment of insomnia for the prevention of mental disorders. Insomnia is well treatable, the first-line treatment being cognitive behavioral treatment for insomnia [16], ∗[17], [18]. CBT-I is a treatment package including behavioral techniques, relaxation, and cognitive therapy. With CBT-I, insomnia symptoms can be significantly reduced in the short- and long-term [19]. As first step into prevention, the question whether insomnia predicts the later onset of different mental disorders has to be answered.

To the best of our knowledge, no meta-analysis investigating insomnia, including daytime symptoms, as a potential risk factor for different psychiatric symptoms or disorders has yet been performed. The objective of the present study was to quantitatively summarize longitudinal studies investigating whether insomnia at baseline constitutes a risk factor for the later onset of a mental disorder.

Section snippets

Methods

The meta-analysis was performed in accordance with the recommendations of reporting for meta-analyses of observational studies in epidemiology [MOOSE, [20]] and the PRISMA statement for reporting systematic reviews and meta-analyses of studies that evaluate health care interventions [21]. Two authors (TG and CK) independently performed the literature search, screened all titles and, where applicable, the abstracts and full texts of potentially eligible studies, and extracted relevant data for

Results

The process of study identification, screening for eligibility, and inclusion is shown in Fig. 1.

Description of the sample

Thirteen primary studies were included into the meta-analysis (Table 1). The total sample (participants with and without insomnia) included 181,798 participants at baseline and 133,967 at the last follow-up time points. Time between baseline and last follow-up was 61 mo on average, whereby five studies had their last follow-up after 12 mo, three studies after 18 mo, and the remaining studies had longer follow-up periods of up to 20 y.

Main results

The results of the meta-analysis are shown in Fig. 2. The main result is that insomnia is a significant predictor for onset of depression (10 studies, OR 2.83, CI 1.55–5.17), anxiety (six studies, OR 3.23, CI 1.52–6.85), alcohol abuse (two studies, OR 1.35, CI 1.08–1.67, and psychosis (one study, OR 1.28, CI 1.03–1.59). In the exploratory analysis across all mental disorders, the model found an OR of 2.60 (CI: 1.70–3.97), indicating that primary insomnia is a significant predictor for later

Risk of bias

Results of the risk of bias assessment, based on the QUIPS risk of bias assessment tool, are shown in Table 2. The ratings are illustrated in three different colors, where green (happy smiley) indicates a low risk, orange (indifferent smiley) indicates a medium risk, and red (sad smiley) indicates a high risk. Interrater agreement (Cronbach's alpha) was between 0.8 and 1.0 for the six assessment dimensions. The risk of bias arising from the study samples (sample description, recruitment,

Publication bias

Due to the small number of studies for the outcomes alcohol abuse (n = 2) and psychotic disorders (n = 1), funnel plots and Egger's tests were only created/computed for the outcomes depression and anxiety. The funnel plots are shown in Fig. 4. Egger's tests were insignificant, indicating that funnel plots were not asymmetric, for both outcomes (depression: t = −1.192, p = 0.268; anxiety: t = −1.268, p = 0.274). However, visual inspection of the funnel plots indicated a certain degree of

Discussion

The present meta-analysis including 13 primary studies evaluated the predictive power of insomnia at baseline for the onset of a mental disorder within the follow-up period. We found that insomnia is a significant predictor for depression, anxiety, and alcohol abuse. One study suggested that insomnia is also a predictor of psychosis. This result remained significant when the analysis was limited to the 11 studies that only included participants without any mental comorbidity at baseline.

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