Researchers found that anxiety may cause insomnia, but depression may not. Instead, insomnia turns out to be a cause for depression.
Anxiety Causes Insomnia but Depression Does Not
Insomnia frequently co-occurs with both anxiety disorders and depression. Many studies of insomnia, anxiety, and depressive symptoms among adolescents have documented statistically significant associations.
Then what is the directionality of this association? In other words, which causes which? To answer this question, in a 2006 study, researchers recruited 1,014 adolescents in the Detroit metropolitan area.
Of the adolescents in this study, 108 or 10.7% met DSM-IV criteria for insomnia during their lifetime, 17% of adolescents had a lifetime history of an anxiety disorder, and 3.6% had a lifetime history of major depression. Between 24% and 43% of those with an anxiety disorder or major depression also met criteria for insomnia.
Researchers conducted in-depth, face-to-face interviews with these adolescents and had some interesting findings:
The association between any prior anxiety disorder and onset of insomnia was significant and moderately strong. In other words, anxiety causes insomnia.
The association between prior insomnia and subsequent anxiety disorders was nonsignificant. In other words, insomnia does not cause anxiety.
Prior depression was not associated with onset of insomnia. In other words, depression does not cause insomnia.
Depression was 3.8 times more likely among those with prior insomnia compared to those without it. In other words, insomnia causes depression.
To sum up, the predominant patterns in the directionality of associations between insomnia and anxiety is from anxiety to insomnia, while that for insomnia and depression is from insomnia to depression.
Anxiety Treatment Improves Insomnia Symptoms
The association between anxiety and insomnia raises the hypothesis that reducing symptoms of anxiety would also reduce symptoms of insomnia.
In a 2014 research study, researchers recruited 102 of patients and treated them with internet-based cognitive behavioral therapy (iCBT) for anxiety and/or depression. 61 patients completed the treatment, and pre- to post-treatment symptom changes were examined.
Insomnia was evident in 40% of the patients in this study. Individuals with insomnia reported more severe symptoms of anxiety and depression than individuals without insomnia.
The results showed that iCBT treatment, which focused on anxiety and/or depression, was associated with reductions in symptoms of insomnia, anxiety and depression. In other words, treatment for anxiety and/or depression appears to improve comorbid insomnia symptoms.
Further, when looking at residual symptoms of insomnia, researchers found that among treatment completers who had remitted from their disorder, only 10% had insomnia post-treatment (compared to 25% at pre-treatment).
Johnson, Eric O., et al. “The association of insomnia with anxiety disorders and depression: Exploration of the direction of risk.” Journal of Psychiatric Research, vol. 40, 2006, pp. 700–708.
Mason, Elizabeth C., and Allison G. Harvey. “Insomnia before and after treatment for anxiety and depression.” Journal of Affective Disorders, vol. 168, 2014, pp. 415–421.