Atypical work-times such as night shifts and very early shifts can affect the quality and quantity of sleep. Short sleep duration and disturbed sleep are associated with a hightened accident risk. Humans and animals are influenced by a biological clock which is genetically determined and synchronised by daylight. The study investigates the impact of the start of working time and chronotype on sleep duration and occupational accidents.Methods
In this cross-sectional study data were collected from about 550 employees in the woodworking and metalworking industry. Analyses were conducted for relationships between chronotype, start of working time, sleep duration and accidents.Result
The average chronotype moves by two hours towards an earlier type from the youngest to the oldest group of employees. Among the subjects without accidents 23% regard themselves as morning types, 69% as intermediate types and 9% as evening types. Among the subjects who had an accident 32% were morning types and 5% evening types. The late chronotypes get the least sleep on workdays and the early chronotypes get the least sleep on work-free days. Significant differences in the sleep duration were found for morning shift workers compared to day workers. A relevant proportion of the sleep deficit is due to the early start of working time.Discussion
The study shows significant chronotype-dependant differences in the sleep duration on work-days and free days. Early chronotypes seem to be unable to compensate their sleep deficit on free days, late types are unable to sleep early in the evening. Results will be useful to identify groups of workers at hightened risk for sleep deficit and sleepiness at work. In this way occupational accidents in shift workers and workers with an early starting time of work could be reduced.