Objectives: The combined effects of age, leisure-time physical activity, smoking, alcohol consumption, and different forms of shift work on the prevalence of sleep complaints and daytime sleepiness were studied among workers in industry, transport, and traffic.
Methods: Altogether 3020 subjects were studied using a psychosocial questionnaire. The participants were currently employed men, aged 45-60 years, from a postal and telecommunication agency, the railway company, and 5 industrial companies. On the basis of a factor analysis of an 11-item sleep questionnaire, the sleep complaints were grouped into the categories of insomnia, sleep deprivation, daytime sleepiness, and snoring. The importance of the shift schedule, age, and life-style factors as simultaneous predictors of the complaints was studied in a logistic regression analysis and an analysis of covariance.
Results: The prevalence of insomnia, sleep deprivation, and daytime sleepiness depended significantly on the shift system. All sleep complaints were more common in 2- and 3-shift work and in irregular shift work than in day work. The prevalence of daytime sleepiness was 20-37%, depending on the shift system. Leisure-time physical activity and alcohol consumption were the most important life-style factors predicting all sleep complaints, except snoring. The effects of physical activity and alcohol consumption differed for different shift schedules.
Conclusions: Different shift systems, also 2-shift work and permanent night work, seem to increase the frequency of sleep complaints. Especially 3-shift work seems to interact with life-style factors by increasing the adverse effects and decreasing the beneficial effects on sleep and sleepiness.