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Novel shift schedules reduce social jetlag

München, 03/12/2015

In the first field study of its kind, LMU chronobiologists found that adapting shift schedules to chronotype improve sleep and reduce social jetlag.

Foto: eyetronic / fotolia.web

We all know the feeling: After an uneasy night’s sleep, one wakes up bleary-eyed and the whole day seems shrouded in a fog. Our physiological rhythms are disrupted. Modern work and appointment schedules often clash with the internal times of our biological clock. “In many people, the discrepancies between our internal time and the temporal demands of the world around us lead to what we have called social jetlag, an environmentally induced perturbation of our natural sleep cycle,” says LMU chronobiologist Professor Till Roenneberg. Social jetlag is a particular problem among shift workers. But Roenneberg and his colleagues have now shown that social jetlag can be reduced by adjusting shift schedules to the worker‘s individual ‘chronotype’. This is the first field experiment where schedules were adjusted to chronotype in a normal working environment.

Both individual sleep duration and sleep timing are genetically predisposed and vary between individuals: Forcing a late chronotype to get up at dawn every day for years on end won’t turn it into an early bird. And a lifestyle that is permanently out of sync with the circadian clock has consequences for health, and can even lead to the development of serious conditions such as atherosclerosis or cancer. “Night work and shift work are particularly unhealthy,” says Roenneberg. “The resulting sleep deficit has detrimental effects on the whole organism, impairing physiological regeneration and repair processes.”

Fitting schedules to chronotypes
As Roenneberg and his team have now demonstrated, a reorganization of shift schedules can at least partially remedy this situation. “Thanks to a farsighted works director at ThyssenKrupp Steel Europe, we were given the opportunity to investigate the effects of a novel scheduling concept that took into account the chronotype of the individual shift worker,” Roenneberg explains.

The researchers began by determining the sleep patterns of those recruited for the study, and assigned them to different chronotype groups, early, late or intermediate. Their shift schedules were then reassigned so that early and late chronotypes did not have to work shifts that were clearly out of phase with their biological clock. In other words, the ‘larks’ were not assigned to the night shift, while the night owls did not have to work the early shift. Intermediate chronotypes served as controls.

Apposite work schedules improve sleep
At the beginning and the end of the 5-month experiment, the LMU researchers ascertained the sleep and activity patterns of their experimental subjects, as well as their general state of health. The analysis revealed that, after the reassignment of shifts, sleep duration on workdays was extended by one hour on average, with a corresponding reduction in social jetlag. In addition, the adjustments in the work schedule were correlated with mild improvements in perceived well-being. Overall, the degree of subjective improvement was greater for the larks than for the owls. This indicates that night shifts are difficult for all chronotypes, which is not surprising, given that even confirmed owls find it hard to remain active throughout the entire night.

The next step
“Taken together, our results demonstrate that, in principle, reorganization of shift schedules is both feasible and effective, can reduce social jetlag and increase sleep duration,” says Roenneberg. “However, our sample size was relatively small, so that further studies with larger numbers of participants should be performed to confirm the results. It would also be interesting to examine to what extent the findings apply to other trades and professions – and to teenagers in schools.” Roenneberg now plans to probe the relationship between shift work, sleep duration and overall health in controlled laboratory experiments. “We already know that sleep duration has broad implications for health. So we hope that our findings will ultimately lead to changes in work schedules and to a new approach to time management in general,” says Roenneberg.
(Current Biology 2015)   göd