The Zurich study

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Abstract
The association of three subtypes of insomnia with psychic and functional syndromes, and the course of insomnia over 7 years were examined in a Swiss cohort of young adults interviewed three times. Specific associations were found between repeated brief insomnia (RBI) and recurrent brief depression (RBD). Continued insomnia (CI) was associated with major depression. All three subtypes of insomnia were associated with anxiety disorders; 52% of insomniacs were free of concurrent anxiety and depression. Insomnia — especially RBI and CI — was also associated with a number of functional complaints, but not with the consumption of alcohol, medicine, or illegal drugs. Insomniacs with RBI and occasional insomnia (OI) experienced more life events and interpersonal conflicts than controls. These findings support the subdivision of insomnia into different subtypes. The longitudinal analysis showed that insomnia tends to reoccur. For subjects with insomnia either at age 21 or 23 years, there was a higher risk of further insomnia at follow-ups. The specific subtype of insomnia at the first occurrence was not predictive for the outcome: all subtypes of insomnia enhance the risk of relapses in a similar way. Insomnia at age 21 is no precursor of the first onset of a depressive or anxiety disorder within a 2-year follow-up. With respect to the course of insomnia over 7 years, the subtypes did not differentiate.

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