Among shift workers
The term shift work describes regular employment outside the normal daytime hours. Therefore, shift workers are likely to experience conflicting demands from work and internal body clock. Most shift workers have at least occasional sleep disturbances, and approximately one-third complain of fatigue .
A Finnish study looked at the combined effects of different forms of shift work, age, leisure-time physical activity, smoking, and alcohol consumption on the prevalence of sleep complaints and daytime sleepiness. 3020 participants 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. The researchers grouped the sleep complaints into the categories of insomnia, sleep deprivation, daytime sleepiness, and snoring. 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. The researchers concluded that different shift systems, also 2-shift work and permanent night work, 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.