Impacts of shift work on sleep and circadian rhythms

Shift work comprises work schedules that extend beyond the typical “nine-to-five” workday, wherein schedules often comprise early work start, compressed work weeks with 12-hour shifts, and night work. According to recent American and European surveys, between 15 and 30% of adult workers are engaged in some type of shift work, with 19% of the European population reportedly working at least 2hours between 22:00 and 05:00. The 2005 International Classification of Sleep Disorders estimates that a shift work sleep disorder can be found in 2–5% of workers. This disorder is characterized by excessive sleepiness and/or sleep disruption for at least one month in relation with the atypical work schedule. Individual tolerance to shift work remains a complex problem that is affected by the number of consecutive work hours and shifts, the rest periods, and the predictability of work schedules. Sleepiness usually occurs during night shifts and is maximal at the end of the night. Impaired vigilance and performance occur around times of increased sleepiness and can seriously compromise workers’ health and safety. Indeed, workers suffering from a shift work sleep-wake disorder can fall asleep involuntarily at work or while driving back home after a night shift. Working on atypical shifts has important socioeconomic impacts as it leads to an increased risk of accidents, workers’ impairment and danger to public safety, especially at night. The aim of the present review is to review the circadian and sleep-wake disturbances associated with shift work as well as their medical impacts. Le travail posté exige des périodes de travail qui sortent du cadre conventionnel des journées “de neuf à cinq”. Les horaires de travail comportent souvent un début de travail précoce, des horaires comprimés avec quarts de 12heures ainsi que des périodes de travail de nuit. Des enquêtes récentes américaine et européenne rapportent qu’entre 15 et 30 % des travailleurs adultes travaillent sur un horaire non conventionnel, incluant 19 % de la population européenne qui rapporte travailler au moins 2heures entre 22:00 et 05:00. La classification internationale des troubles de sommeil de 2005 estime qu’un désordre de sommeil lié au travail posté peut être observé chez 2–5 % des travailleurs. Ce désordre se caractérise par de la somnolence excessive et/ou des perturbations du sommeil pendant au moins un mois en relation avec l’horaire atypique de travail. La tolérance d’un individu au travail posté deme