Conference Discusses the Social Jet Lag Syndrome

Video - Till Roenneberg

The modern lifestyle has led many individuals to develop what chronobiologist Till Roenneberg, professor and vice-president of the Medical Psychology Institute at Ludwig-Maximilians University (Germany), defined as “social jet lag” syndrome – the physical and mental impairment caused by a mismatch between the biological clock that regulates an organism’s physiological activities and the social clock that determines one’s daily personal and work commitments.

Roenneberg spoke of the causes and effects of this syndrome at the conference Circadian Behavior and Sleep in the Real World, held on April 21 as part of the program of the Intercontinental Academia (ICA) on the issue of “Time.”

According to the professor, social jet lag can be defined as a discrepancy between internal body rhythms and external environmental rhythms. It is very similar to what happens when a traveler crosses several time zones in succession: the sudden changes lead the body clock (which is adjusted to the time of the place of departure) to conflict with the local clock.

Unlike ordinary jet lag, however, the effects of which are transient, social jet lag is chronic, forcing individuals to fight systematically against their own biological clock in order to cope with the demands of everyday life – and this include ever-longer working hours and greater difficulties to reconcile professional and personal life.

“Everything in our body is controlled and organized by the circadian system. The circadian system, in turn, is not organized by the social clock, but rather by the clock of the Sun, by the clock of light & dark. So there will always be a discrepancy between what society wants us to do and what, under the conditions of modern life, our body wants us to do,” noted Roenneberg.

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Some people compensate this discrepancy between biological and social rhythms by extending their period of activity and reducing their period of repose. According to Roenneberg, those who suffer from social jet lag are generally early risers who remain active until late at night to cope with their daily commitments. In the end, however, things don’t add up for them: they sleep less than eight hours a day and are therefore chronically sleep-deprived.

One can measure this “negative sleep balance” by comparing the pattern of their circadian behavior during weekdays, governed by the social clock, and during their free days, governed by their biological clock. “If we measure the difference between both patterns, we will obtain a quantifiable measure of what we call ‘social jet lag’,” said the professor.

The afflictions of modernity

The negative sleep balance is at the root of many afflictions of modern society, especially those related to metabolic problems. “The greater the social jet lag, the greater the likelihood of becoming obese, developing diabetes, using drugs, smoking to relieve stress, and drinking alcohol to slumber off when one is not yet ready to sleep,” warned Roenneberg .

The implications of social jet lag also extend to the realm of behaviors. According to the chronobiologist, one of the first qualities that disappear when someone sleeps too little is social competence: “You become a true psychopath if you don’t sleep enough.”

For him, the social jet lag syndrome is associated with the idea that sleep keeps us from becoming more productive: “People tend to sleep one hour less in order to remain active for one hour more. Yet, sleeping does not mean ceasing to be active, but rather preparing the body and the mind for activity.”

He explained that simple math underlies this statement: “If someone sleeps one hour less, depriving himself of 1/8 of his sleep period, he only gains 1/16 in terms of activity. On the other hand, his efficiency is reduced by about 1/20.”

The result, he said, is a vicious cycle – one that has become endemic in the United States. “You lose efficiency, so you have to work more and more; to work more, you have to sleep less; and by sleeping less, you lose efficiency.”

In his assessment, the widespread use of alarm clocks is evidence that overall people sleep less than they should. “What is the fundamental issue underlying the use of an alarm clock? That we have not completed our biological sleep period! Otherwise, we would need no help to wake up,” he warned. “We must change our attitude toward sleep,” he added.


In addition to propelling social jet lag, the modern lifestyle also contributes to an extreme expression of the so-called chronotypes – the classification of individuals according to the preferences of their body regarding the time they perform daily activities such as sleeping, waking up, working out and exercising the mind.

There are two main chronotypes: the “morning people,” who sleep and rise early, and reserve the night period to sleep; and the “evening people,” who prefer to sleep and wake up late, even if that means dedicating part of the day to sleep.

Roenneberg said that, in terms of their circadian behavior, these two chronotypes are growing farther and farther apart because of how the patterns of exposure to natural light are changing in the modern age.

According to him, throughout the course of evolution, our biological clock was synchronized with a light/dark cycle regulated by exposure to sunlight: “The environment in which we were synchronized during the last thousands of years was one of much light during the day and no light at all at night. The morning and evening chronotypes existed, but the distance between them was not significant.”

However, the dissemination of electric lighting and the habits of modern life have imposed different levels of exposure to solar and artificial light. Indeed, the luminous signals that help synchronize internal body rhythms and external environment rhythms are being minimized.

Roenneberg used the ICA’s own dynamics as an example: in daytime, when people should normally be exposed to the Sun, participants were confined indoors, with little natural light; at night, on the other hand, when the body should be in the dark, they were exposed to a prolonged period of artificial light. “We are darkening the day and illuminating the night. And this light is increasingly turning us into evening people,” he said.

According to him, exposure to artificial light at night would hardly make a farmer become an evening person, because, when working outdoors, under the Sun, he would signal to the biological clock that sunlight, stronger and natural, was the real light. “It is the contrast between light and dark that synchronizes our biological clock, making us sleep from 10 pm to 6 am,” he said.

In Roenneberg’s view, unlike what is commonly thought, being an evening person does not imply any type of pathology. “There is no innate timing of the circadian clock,” he explained, pondering that sleeping and waking up later is “a natural reaction to the environment where one lives, a normal way for the circadian clock to synchronize a body that is not being sufficiently exposed to light.”