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"Social jetlag"

School and work times ignore the biological clock

Munich, 03/28/2006

If you want to make an owl happy as a lark - throw away the alarm clock. Individual genes that make up our biological, circadian clock predispose a person's so-called chronotype, with early-rising 'larks' and late-working 'owls' marking the extremes. Most people are mild to moderate owls – when free to choose, i.e., when obeying their circadian clock, they sleep and wake later than on work days which are predominantly scheduled for larks. The result is a misalignment of biological and social timing which leads to a special form of jetlag, as Munich researchers report in Chronobiology International. Till Roenneberg at the Ludwig-Maximilians-Universität (LMU) München and his team coined the term 'social jetlag' for this phenomenon after analyzing more than 500 questionnaires probing people's sleep habits and sleep quality, their well-being as well as their use of stimulants like caffeine, nicotine and alcohol. “During the work week, owls suffer from ‘social jetlag’,” says Roenneberg. “The symptoms are quite similar to those we experience when crossing time zones, but the potential consequences resulting from ‘social jetlag’ may last for as long as their working life.”

Nowadays, the majority of people are mild to extreme owls predominantly because they do not get enough light. Outdoor light is 50 to 1000 times brighter than indoor lighting, and bright light – especially in the first half of the day - is essential to advance the circadian clock. Individual chronotypes not only depend on genes and light conditions but also on age. Teenagers usually are extreme owls which makes it especially hard to follow the usually early school times. “Their circadian clock commonly allows teenagers to fall asleep sometime between midnight and 4 a.m.,” says Roenneberg. “Getting up at 6 a.m. corresponds to their biological midnight. Teenagers can be compared to shift workers suffering from similar problems and symptoms as older people who permanently work an early shift starting at 4 a.m..” The results of this study show that owls not only accumulate a severe sleep deficit during the work week but also suffer from reduced sleep quality and day-time fatigue. Owls, however, sometimes take revenge on weekend nights by making their lark friends stay up beyond their usual bedtime. Yet, larks tend to wake up at the same early hours regardless how late they went to bed and, thus, also show symptoms of 'social jetlag'.

Sufferers from chronic 'social jetlag' are more likely to use stimulants like caffeine, nicotine and alcohol. Smoking increases with the amount of 'social jetlag', similar to its higher prevalence among shift workers. “Nicotine abuse is often a sign of mal-adaptation to social requirements,” says Roenneberg. “Sleep problems, depression, and smoking predominantly occur when the biological and the social time schedules don't match.” This is of great importance because smokers tend to start smoking as teenagers when their 'social jetlag' is most severe. It is known that owls tend to be less successful in school compared to larks which could easily be explained with their chronic sleep deficit and having to perform at the wrong time of day. “Schedules should consider the circadian timing of both teenagers and individual adults,” says Roenneberg, “which would take a major change in society.”

"Social Jetlag: Mis-alignment of Biological and Social Time",
Marc Wittman, Jenny Dinich, Martha Merrow, Till Roenneberg,
Chronobiology International, 2006

Prof. Dr. Till Roenneberg
Center for Chronobiology at the LMU Munich
Tel.: +49 89 218075-239
Fax: +49 89 218075-615

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