Objective: This study aims at assessing the relative impact of psychological factors on insomnia among daytime workers. Background: Insomnia affects 5-45% of non-shift workers, making it a serious public health concern. Methods: The study population was 3435 male civil servants aged 35 years and over. A self-administered questionnaire survey was conducted in 2002. Annual health examination data compiled in the same year were also obtained. Insomnia was assessed in three domains: difficulty initiating sleep (DIS), difficulty maintaining sleep (DMS), and poor quality of sleep (PQS). Association of each factor with insomnia was examined by age-adjusted logistic regression models. Factors significantly associated with insomnia in age-adjusted analyses were entered in the stepwise logistic regression models to test the relative impact of each factor. Results: Prevalence of insomnia was 12.3% (DIS), 20.4% (DMS), and 32% (PQS). In stepwise logistic models, high perceived stress was associated with all types of insomnia with odds ratios (95% confidence interval) of 2.27 (1.58-3.26), 2.15 (1.57-2.95), and 2.96 (2.19-3.99), for DIS, DMS, and PQS, respectively. Poor psychological well-being or not having confidants was also associated with insomnia. Somatic conditions such as illnesses or history of hospitalization were related to DIS and DMS. Conclusions: Psychological factors were strongly associated with DIS and PQS after controlling for possible confounders. In dealing with insomnia, such factors must not be neglected.
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