The effects of the number of consecutive night shifts on sleep duration and quality.

Objectives The organization of night shift work affects sleep duration and quality. The aim of this study was to investigate the effects of the number of consecutive night shifts on sleep duration and quality among police officers with night shift work as part of their normal schedule. Methods This quasi-experimental, within-subject crossover study included 73 police officers. All participants performed three work schedules: two, four and seven consecutive night shifts followed by the same number of recovery days, ie, day work or days off (2+2, 4+4, and 7+7). Sleep assessed through sleep diaries and actigraphy after all night shifts and recovery days (totaling 26 days) was compared by use of repeated measures analysis. Results Participants experienced shorter sleep duration (with and without naps), more premature awakening, less difficulty falling asleep, and more non-refreshing sleep after night shifts compared with recovery days. Sleep duration and quality did not change with increasing number of consecutive night shifts. Sleep was shorter and of poorer quality after the last night shift in the 2+2 and 4+4 work schedule compared with the second and fourth night shift, respectively, in the 7+7 schedule. Conclusion Sleep duration was reduced after night shift work and did not increase with more consecutive night shifts, which leads to accumulated sleep debt. Sleep duration was shortest and sleep quality was poorest after the last night shift in a series of night shifts.