BACKGROUND

Insomnia is highly prevalent and impairing but also highly comorbid with other chronic physical/mental disorders. Population-based research has yet to differentiate the role impairments uniquely associated with insomnia per se from those due to comorbidity.

METHODS

A representative sample of 6791 adult subscribers to a large national US commercial health plan was surveyed by telephone about sleep and health. Twenty-one conditions previously found to be comorbid with insomnia were assessed with medical/pharmacy claims data and validated self-report scales. The Brief Insomnia Questionnaire, a fully structured, clinically validated scale, generated insomnia diagnoses according to inclusion criteria of DSM-IV-TR, ICD-10, and Research Diagnostic Criteria/International Classification of Sleep Disorders: Diagnostic and Coding Manual, Second Edition. The World Health Organization Disability Assessment Schedule-II assessed number of days in the past 30 when health problems prevented respondents from conducting their usual daily activities. Regression analyses estimated associations of insomnia with days-out-of-role controlling comorbidity.

RESULTS

Insomnia was significantly associated with days-out-of-role (.90 days/month) in a gross model. The association was reduced when controls were introduced for comorbidity (.42 days/month). This net association did not vary with number or type of comorbid conditions but was confined to respondents 35+ years of age. Insomnia was one of the most important conditions studied not only at the individual level, where it was associated with among the largest mean days-out-of-role, but also at the aggregate level, where it was associated with 13.6% of all days-out-of-role.

CONCLUSIONS

Insomnia has a strong net association with days-out-of-role that does not vary as a function of comorbidity.