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Published on January 6, 2014 at 5:15 PM
By Lucy Piper, Senior medwireNews Reporter

Short and long sleep duration, but not insomnia, predict a chronic course of depressive and anxiety disorders independent of symptom severity, research indicates.

Patients with persistent depression or anxiety were more likely to have insomnia than those without persistent disorders. However, insomnia was not independently associated with persistence after accounting for symptom severity.

“Our results also show that it is important to differentiate between insomnia and sleep duration, since there was no interaction effect between insomnia and sleep duration,” the researchers note in the Journal of Clinical Psychiatry.

They studied 1069 individuals aged an average of 42.7 years with DSM-IV-diagnosed depression or anxiety, 59% of whom had insomnia, diagnosed as a Women’s Health Initiative Insomnia Rating

Scale score of 9 or above. At 2-year follow-up, persistent depressive and/or anxiety disorder, according to the Composite International Diagnostic Interview, was seen in 61.1% of patients.

Patients who reported sleeping an average of 10 hours or more per night were a significant 2.52 times more likely to have persistent (6-month diagnosis) depression and/or anxiety over 2 years of follow-up than patients who reported sleeping for a normal 7 to 9 hours per night. This was after adjusting for sociodemographic characteristics, chronic medical disorders, psychotropic medication, and symptom severity.

Those who reported short sleep durations of 6 hours or less per night were a significant 1.64 times more likely to have persistent depression and/or anxiety, but, as with insomnia, significance was lost after adjustment for symptom severity.

Both long and short sleep duration were also independently associated with a chronic course (no remission, and at least mild symptoms for 2 years of follow-up) of depression and/or anxiety, increasing the risk a significant 2.91-fold and 1.50-fold, respectively.

When the researchers looked at the effects of sleep duration on the course of depression and anxiety separately, they found that both long and short sleep duration predicted a chronic course of anxiety symptoms, with significant odds ratios of 7.73 and 1.62, respectively. The same was true for chronic depressive symptoms, with corresponding odds of 4.34 and 2.03.

Long and short sleep duration also predicted persistent depressive disorder, at significant odds ratios of 2.52 and 1.49, respectively, but neither predicted persistent anxiety disorder.

“[O]ur study adds significant information on the impact of sleep disturbances on the course of psychopathology,” say lead researcher Josine van Mill (EMGO Institute for Health and Care Research, Amsterdam, the Netherlands)and colleagues.

They add: “In clinical practice, routinely asking for sleep duration might identify subjects at risk for a chronic course.”

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