Aligning work and circadian time in shift workers improves sleep and reduces circadian disruption.

Sleep loss and circadian disruption-a state of misalignment between physiological functions and imposed sleep/wake behavior-supposedly play central roles in the etiology of shift work-related pathologies [1-4]. Circadian entrainment is, however, highly individual [5], resulting in different chronotypes [6, 7]. Chronotype in turn modulates the effects of working times: compared to late chronotypes, earlier ones sleep worse and shorter and show higher levels of circadian misalignment during night shifts, while late types experience more sleep and circadian disruption than early types when working morning shifts [8]. To promote sleep and reduce the mismatch between circadian and working time, we implemented a chronotype-adjusted (CTA) shift schedule in a factory. We abolished the most strenuous shifts for extreme chronotypes (i.e., mornings for late chronotypes, nights for early ones) and examined whether sleep duration and quality, social jetlag [9, 10], wellbeing, subjective stress perception, and satisfaction with leisure time improved in this schedule. Intermediate chronotypes (quartiles 2 and 3) served as a control group, still working morning (6:00-14:00), evening (14:00-22:00), and night (22:00-6:00) shifts, with two strenuous shifts (out of twelve per month) replaced by evening ones. We observed a significant increase of self-reported sleep duration and quality, along with increased wellbeing ratings on workdays among extreme chronotypes. The CTA schedule reduced overall social jetlag by 1 hr, did not alter stress levels, and increased satisfaction with leisure time (early types only). Chronotype-based schedules thus can reduce circadian disruption and improve sleep; potential long-term effects on health and economic indicators need to be elucidated in future studies.

Vetter C ，Fischer D ，Matera JL ，Roenneberg T ... -  《-》

Chronotype modulates sleep duration, sleep quality, and social jet lag in shift-workers.

Juda M ，Vetter C ，Roenneberg T 《-》

Day and night shift schedules are associated with lower sleep quality in Evening-types.

Martin JS ，Laberge L ，Sasseville A ，Bérubé M ，Alain S ，Houle J ，Hébert M ... -  《-》

A unique, fast-forwards rotating schedule with 12-h long shifts prevents chronic sleep debt.

Fischer D ，Vetter C ，Oberlinner C ，Wegener S ，Roenneberg T ... -  《-》

Sleep timing, chronotype and social jetlag: Impact on cognitive abilities and psychiatric disorders.

Sleep timing is controlled by the subtle interplay between circadian and homeostatic oscillators which, according to their endogenous properties, allow beings to feel spontaneously that it is time to go to bed or wake up in synchrony with the earth's light/dark cycle. In humans, however, social time and nocturnal artificial light modify sleep timing. Our modern lifestyle and artificial nocturnal light delay our bedtime, make us wake up, and lead to a greater intraindividual variability in sleep timing. Depending on the constraints that social time places on us, our sleep timing may be in or out of phase with the internal circadian timing determined by the circadian clock. When a person's social time is out of phase with their circadian time, they may be considered to suffer from circadian disruption or 'social jetlag'. There are interindividual differences in sleep timing that are known as morningness-eveningness preferences or chronotype, e.g. late chronotypes go to bed later. Chronotype may be assessed in terms of differences in kinetic homeostatic sleep pressure, intrinsic circadian period (ICP) and/or phase angle entrainment. In addition, chronotype depends on genetic and age-related factors, e.g. it gets earlier as people grow older. The social time of late chronotype individuals during week days is not adapted to their circadian time, unlike on free days. This results in social jetlag and circadian disruption, which in turn induces a chronic sleep debt due to a late bedtime and an early wake time, which is compensated on free days but only partially. Sleep and circadian clock disruption generally alter cognitive performance (alertness, attention, memory, higher-order executive functions such as response inhibition and decision-making) but their impact remains to be clarified. When subjects adopt their preferred sleep timing, a "synchrony effect" often appears with chronotypes performing better during daytime at optimal than at suboptimal timing (late chronotypes perform better in the evening, early chronotypes in the morning). Evening types appear to be cognitively more vulnerable to suboptimal times than morning types, probably because they have to deal with social jetlag and the "wake effort" period after awakening. Circadian disruption, but not chronotype, may impact attentional/inhibitory performance (more impulsivity and inattention). Strong associations have been found between mood disorders or attention deficit hyperactivity disorder (ADHD) and chronotype, with these psychiatric disorders typically being overrepresented in evening types. The association between social jetlag and these psychiatric disorders is less obvious. Social jetlag can be corrected by reducing exposure to evening light, although eveningness may be considered as a lifelong factor predisposing to depression or inattention.

Taillard J ，Sagaspe P ，Philip P ，Bioulac S ... -  《-》