DSM-IV psychiatric comorbidity according to symptoms of insomnia: a nationwide sample of Korean adults

The diagnosis of insomnia is based on the presence of four different symptoms: difficulty in initiating sleep (DIS), difficulty
in maintaining sleep (DMS), early morning awakening (EMA), and non-restorative sleep (NRS). This study investigated the differences
in sociodemographic correlates and psychiatric comorbidity between the four symptoms of insomnia in the general population
of South Korea.

A sample of the population aged 18–64 (N = 6,510) was questioned using a face-to-face interview. Insomnia was defined as having at least one of the four following
symptoms three or more times per week: DIS, DMS, EMA, and NRS. Psychiatric disorders were evaluated using the Korean version
of Composite International Diagnostic Interview. Logistic regression analysis was used to test each of the sleep outcomes
(DIS, DMS, EMA, or NRS) for an association with sociodemographic and clinical variables.

The prevalence of DIS, DMS, EMA, and NRS were 7.9 % (95 % CI 6.6–9.5 %), 7.9 % (95 % CI 6.5–9.6 %), 4.9 % (95 % CI 3.9–6.0 %),
and 14.8 % (95 % CI 12.6–17.4 %), respectively. The overall prevalence of insomnia was 19.0 % (95 % CI 16.1–22.2 %). Being
separated, divorced, or widowed, being single, having a part-time job, having a psychiatric illness, and having a physical
illness were all significantly related to insomnia. Older age also increased the risk of DMS and EMA, and younger age was
a risk factor for NRS. The presence of most psychiatric disorders was significantly related to insomnia. However, the relationship
between the psychiatric illness and each insomnia symptom varied and was dependent on the insomnia symptom.

Most psychiatric disorders were significantly associated with each insomnia symptom in different ways. Differences in sociodemographic
and clinical correlates between the four insomnia symptoms implied the heterogeneous characteristics of insomnia as defined
by the current diagnostic criteria.