Social jet lag leads to obesity

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Less and less sleep: With social jetlag, overweight threatens

It is not just long-distance travel across multiple time zones that can trigger jet lag. Anyone who constantly works at different times due to shift work or has irregular leisure behavior also suffers from the consequences of disturbances in the internal clock. According to a study, up to 70 percent of people in western industrialized countries are affected by “social jetlag”. Researchers warn of the unpredictable consequences for health.

Working life causes jet lag
Anyone who has already traveled by plane from Germany to the United States will have felt the effects of jet lag. Difficulty falling asleep, fatigue, headaches and even migraines can be clearly noticeable symptoms here. However, according to a new scientific study, people suffer from jet lag not only after long flights over numerous time zones. Different working or school times as well as irregular leisure activities can also mess up the organism and thus the rhythm of the internal clock. At least that is what scientists from the University of Munich report to the study director Chronobiologist Till Roenneberg. According to the research team, up to two thirds of the people in the western industrialized countries are affected by the health consequences that this entails.

In the journal Current Biology, the researchers report on a long-term study that lasted over ten years. Around 65,000 test subjects filled out a questionnaire online at regular intervals. The subsequent data analysis showed that living against the internal clock increases the risk of being overweight and obese. The acquired obesity threatens “serious secondary diseases such as metabolic disorders such as diabetes”. In addition, "obesity has reached a scale of crisis in industrialized societies."

With overweight tendency to obesity
A closer look at the data showed, however, that the context turned out to be a correlation. Only study participants who already exceeded the body mass index (BMI) of 25 showed an increase in weight in the course. From a value of 25, people who are not overly trained already speak of being overweight. On the other hand, those who had a BMI value below 25 mostly did not show any significant weight gains. In addition, it could be seen that the effect only occurred when the jet lag exceeded a time threshold of two hours. With a "small jet lag" of less than an hour, the researchers even observed a statistically calculated decrease in body weight.

Scientists remain undisputed that sleep disorders or "poor sleep" endanger health. In essence, it is not just about the length of sleep, but also the time of sleep. Doctors suspect that sleep behavior is also genetically determined. There are various “chronotypes” that are divided into late or early risers. In this context, sleep researchers also speak of “owls” or “larks”. In addition, people's need for sleep differs. Some people need more sleep and others less. Those who get up late and are among the “owls” cannot do anything for their less socially recognized disposition. However, they are also more susceptible to "social jet lag".

Based on the data, around 70 percent of people in western countries are affected by chronic jet lag that lasts at least one hour. About 35 percent even showed jet lag for two hours or more. The researchers also observed a steady decrease in sleep duration over the past decade. People under the age of 20 are most affected. They are very often among the “owls”, although they usually have to go to school early on weekdays.

How much sleep is missing as a result can be seen from the school-free days. On average, teenagers sleep three hours more on a Sunday than during the school week. Only in the case of small children and the elderly do the times of getting up and going to bed remain the same over the week and on weekends.

Less and less time to sleep
"The decrease in sleep duration has been exacerbated on weekdays in the past decade," the authors write in the study report. This is worrying, because it also increases social jet lag. During the weeks, the duration of sleep decreases continuously, while more and more people tend to "chronotypes" (owls). People are also exposed more to natural, artificial light. The weak light in apartments and offices is "inadequate clock" compared to sunlight. This also adjusts the "inner clock".

"Our results show that life against the clock can be a factor in the obesity epidemic," the researchers write in their summary. The observations should also play a role in the discussion during the implementation of summer time, because the time change contributes to social jetlag. "Our data suggests that improving the correspondence between biological and social clocks can help treat obesity." (Sb)

Read on:
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Biorhythm suffers from time change

Image: Berwis /

Author and source information

Video: The clock in our genes and in every cell of your body. Joseph Takahashi. TEDxSMU 2013

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