The prevalence and pattern of insomnia in Japanese industrial workers: relationship between psychosocial stress and type of insomnia.

We examined the prevalence of insomnia among Japanese male industrial workers and analyzed the effect of psychosocial stress on the prevalence of three types of insomnia: 'difficulty in falling asleep', 'frequent sleep interruption' and 'early morning arousal'. The study population consisted of male day workers (n = 319) in a manufacturing heavy industry company located in Nagasaki City, Japan. The subjects answered a questionnaire consisting of six sleep-related items and 24 questions related to occupational and private life conditions. A total of 271 men (average age 40.9 years) completed the questionnaire; a response rate of 85%. Insomnia within the month preceding the survey was present in 27.7% of the workers (75/271). Multiple logistic regression analysis demonstrated that different psychosocial stressors were associated with different types of insomnia. Visual display terminal (VDT) work overload was significantly associated with all types of insomnia, while 'over-involvement in the job' was associated with difficulty in falling asleep and early morning arousal. Our results demonstrated that the prevalence of insomnia in Japanese workers is similar to that reported among European and American general adult population. Our results also indicate that the use of VDT in the workfield is associated with insomnia.