THE BLOG

Unlocking the Science of Social Jet Lag and Sleep: An Interview With Till Roenneberg

Professor Till Roenneberg is a leading researcher of chronobiology, or biological rhythms, in the rapidly expanding field of sleep science. As the Head of Human Chronobiology at the Institute of Medical Psychology at Ludwig-Maximilian University (LMU) of Munich, Roenneberg has unlocked the secret to how our unique internal clocks affect how and when we sleep -- and why some of us are burdened with the disadvantage of living in a time zone which is not our own.

Roenneberg has incorporated his extensive knowledge of chronobiology and sleep habits into his own life, and he no longer uses an alarm clock in the morning (unless he's catching a flight).

I spoke with Roenneberg about the effects of "social jet lag" on our behavior and performance, the changes schools and companies can make to accommodate our biological needs, and the aggressive campaign required to take away the "coolness" of sleep deprivation.

What is social jet lag?

A biological clock is ticking in every person, producing an individual daily timing. This defines a person's unique "chronotype," which can vary greatly between individuals. For some people, internal midday may coincide with external midday. Others can reach their internal midday several hours before or after external midday. Social jet lag measures this difference between our external social timing and that of our internal clock.

Why does this difference exist within the population?

We have changed our environment drastically. Internal clocks evolved in very bright days and dark nights. With decreasing exposure to daylight from working inside and increased exposure to artificial light after sunset, we have drastically weakened the signals used by our clocks to synchronize to the 24-hour day.

The light intensity we get inside buildings is up to 1,000-fold less light than outside. And with our electronics and artificial lighting, the only time we are in darkness is when we sleep. As a consequence, the biological clocks in most of us become very late. The difference between the earliest and the latest chronotypes in a population that works outside during the day and is exposed to darkness after sunset is about two hours. In urban societies, this difference is almost twelve hours.

Our clocks still work the same as they did for our ancestors. If you take urban dwellers with very different chronotypes on a camping trip, these differences will be reduced to less than two hours. The delay of our biological clocks due to our urban lifestyle has not translated into later work times. Eighty percent of us therefore need an alarm clock to wake up in time for commuting to work. This discrepancy gives rise to social jet lag.

What are the consequences of social jet lag?

Your sleep is reduced because your signal to fall asleep comes late in the evening. So it takes longer to fall asleep, and your alarm clock goes off early the next morning. We get much less sleep during the workweek, one to two hours less than if we weren't using alarm clocks -- and that sleep debt accumulates.

Your cognitive performance is reduced greatly. Memory capacity is reduced. Social competence is reduced. Your entire performance is going to suffer. The way you make decisions is changed. Simply, if we are sleep deprived, we behave quite differently than when we sleep enough.

The problem is that we are living in a time zone that is not our own. The fact that our biological timing is so different than our social timing also affects our metabolism and immune system. We're prone to becoming fatter -- even if we eat the same amount of food -- because we're forced to eat at the wrong internal times. The chances that you develop diabetes are higher, and the chances you develop an illness you would have otherwise been able to fight off is also higher.

Can we take steps to avoid social jet lag, like increasing our exposure to light in the morning and decreasing our exposure to light in the evening?

Yes, these steps can be taken -- but they must be kept to every day. If not, the circadian clock will revert to its original state. Exposing yourself to light in the morning is helpful, just not too early -- between 8 a.m. and 9 a.m. should be safe for most of the population. In the evening, you can wear dark glasses or go into a dark room without any artificial light -- which is challenging. The least you can do is change the settings on your electronics so that they don't give off blue light, which is the most effective wavelength for adjusting the circadian clock (there are free apps out there that do this for you).

How can our workplaces adapt to our unique sleep needs?

We need brighter light in our buildings, without necessarily using more power. Light from the roof could be funneled into the ceilings of each room. Any artificial light that we use should be dynamic -- after sunset, it should change its color composition to exclude the blue part of the light spectrum.

Our work times need to be much more flexible. We are aspiring in the industrialized world to be a 24/7 global player, and, therefore, it's much better to leave the work times up to the individual. Statistically, you will still have the majority of people at work at certain times -- and it will be a "double winning" situation. During the day, people will be better performers and producers, and their social competence will be higher, fostering better teamwork. During the nights on workdays, they will sleep better and longer, preventing the many known negative effects of sleep deprivation on health. They will also sleep less on their free days. It is an enormous waste of private quality time if you have to sleep for half of your free days during the weekend to catch up on the sleep you lost on workdays.

Why aren't more companies doing this already?

The American culture has very little respect for the inactivity of sleep. It's almost as if you are a second-class citizen if you need sleep. But if you lengthen your wake time, you may reduce your efficiency. If you reduce your efficiency, you don't get as much work done. The American worker then sleeps even less because they have more work to do. You get into this downward spiral that nobody thinks about it modern culture.

How does this apply to children and teenagers with strict school schedules?

Adolescents have naturally later internal clocks, and in Germany many schools start before 8 a.m. Studies have shown that late chronotypes achieve lower grades. The difference will disappear once students go to university, where they often have more control over their schedules. But since school grades determine university enrollment, late types are clearly discriminated in their life planning.

In those cases where schools cannot be pushed to a later start time, at least rules should be introduced excluding exam times before 11 a.m. Although not taking care of the discrimination in learning, it would at least take care of the exam-side of the discrimination.

You've discussed the stigma around politicians who smoke, and how that contrasts sharply with the way they tout their sleep deprivation. Tell me more about this:

No politician would smoke in front of a camera, but all politicians clearly declare -- and show it in their faces -- how little they have slept. We know how important sleep is, but they convey to the world that sleep deprivation is good.

The stigma against smoking did not come overnight. It was an enormous and extremely costly campaign of education and psychological warfare. We had to take away the "coolness" of smoking, which was so ingrained in our culture from the tobacco industry. People who portray sleep as unimportant are in a way the modern "tobacco industry." We desperately need a pro-sleep campaign of equal or greater budget as the anti-smoking campaign -- a campaign that takes the "uncoolness" out of sleep.