The Bi-directional Association Between Insomnia and Anxiety
Abstract
Both insomnia and anxiety are common complaints, but while insomnia is a diagnostic criterion for several mental disorders, anxiety is not a criterion for primary insomnia. Numerous studies have shown a high rate of co-morbidity between anxiety disorders and insomnia. The relationship is bi-directional since insomnia contributes to the development of anxiety disorders and anxiety results in insomnia. Four relevant models of co-morbidity are discussed: one disorder represents a predisposition or vulnerability; a common cause exists for insomnia and anxiety disorders; although not casually related, the presence of one disorder influences the presentation, course or outcome of the other; and residual effects of a remitted disorder influence the presentation and the course of the other. Worry seems to be a common affective factor in both anxiety disorders and insomnia. We could not identify any naturalistic outcome and only a few treatment studies that covered both disorders. Treatment studies of post-traumatic stress disorder (PTSD), panic disorder and generalised anxiety disorder (GAD) with both anxiety and insomnia as outcome measures showed variable improvement of both pharmacotherapy and cognitive–behavioural therapy. In treatment programmes for hypnotic discontinuation, the level of anxiety was a key factor for success or not. Researchers on insomnia and anxiety disorders should have more contact, since they have much in common.Insomnia, anxiety, anxiety disorders, co-morbidity
Insomnia is a subjective complaint of difficulty falling or staying asleep or not being restored by sleep. Insomnia is both a symptom of sleep disorders, somatic diseases and mental disorders and a disorder in its own right. Anxiety is an abnormal or overwhelming sense of apprehension and fear often marked by physiological signs (such as sweating, tension and increased pulse), by doubt concerning the reality and the nature of the threat and by self-doubt about one’s capacity to cope with it. Anxiety is also a symptom of mental disorders and somatic diseases, and various anxiety disorders are defined according to the type of anxiety symptoms. Several classifications of both insomnia and anxiety are used, but this review will mainly stick to the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV), where insomnia is divided into either primary or secondary to other disorders/diseases, and the sleep problems must have a duration of at least six months. In DSM-IV both post-traumatic stress disorder (PTSD) and generalised anxiety disorder (GAD) have sleep disturbance as a diagnostic criterion. By contrast, anxiety is not a diagnostic criterion of primary insomnia, but the reverse is true for some parasomnias.
Numerous studies have shown a high rate of co-morbidity between anxiety disorders and insomnia. The relationship is bi-directional since insomnia contributes to the development of anxiety disorders, and anxiety disorders result in insomnia. The character of this bi-directional relationship will be elucidated through a selective review of recent studies.
Epidemiology and Co-morbidity
DSM-IV-defined chronic insomnia has a 12-month prevalence of 6–12% in the population, while the prevalence of anxiety disorders is approximately 15–20%. In the National Comorbidity Survey Replication (NCS-R), insomnia was observed in 32.5% of those who had an anxiety disorder and the odds ratio was 4.0 compared with persons without these disorders.1 A similar odds ratio was reported in a Swedish community-based study.2
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