Jetlag from Work - in the Same Time Zone

Social jetlag and circadian clock discrepancies with real life are linked to obesity

(RxWiki News) "Living against the clock," forced into a schedule because of a job or other responsibilities that conflicts with your natural internal clock, may be contributing to weight gain.

Your circadian rhythm, or clock, determines when you naturally feel you need to sleep and when you would naturally wake up and stay awake.

"Social jetlag" is the "discrepancy between circadian and social clocks, which results in chronic sleep loss," according to a recent study showing that such a condition is linked to a higher body mass index, a measurement used to classify obesity.

"Choose activities that adhere to your natural sleep patterns."

Lead author Till Roenneberg, of the Institute for Medical Psychology at the University of Munich in Germany, and colleagues are in the process of creating a massive database of human sleep/wake behavior that they will turn into a world sleep map.

Because circadian clocks also regulate the body's energy levels, researchers are learning more about the ways disrupted circadian clocks can play a part in weight problems.

Sleep is also, however, strongly influenced by social pressures, such as school schedules and work schedules.

Roenneberg's team has been computing everything related to sleep from a large, long-term study of over 64,000 people.

For this particular study, looking at a possible connection between a person's weight and how well their work lives conformed to their own natural biological clock, they divided participants in the study into two groups.

One group, including 43,308 people, were those with a body mass index (BMI) below 25, which is normal. The other, with a total of 20,731 people, had a BMI at or above 25, which is overweight.

The researchers they ran a series of calculations to see whether a person belonged in one or the other group in terms of their age, gender and average amount of sleep, as well as their "chronotype," which refers to whether they tend to be an early bird or night owl.

A person's chronotype can play a role in how much social jetlag that person might experience: night owls generally have a tougher time conforming to standard 9am to 5pm work schedules, for example.

The researchers also calculated in whether a person experiences social jetlag, which they determined by calculating the difference between a person's midpoint of sleep on workdays to their midpoint of sleep on "free days," where they could sleep as they pleased and did not use an alarm clock. (Those who used alarm clocks on free days were excluded.)

Roenneberg and colleagues found the expected correlation between weight and age (people get heavier as they get older), and they saw that longer sleep times was slightly linked to a lower likelihood of being overweight.

However, even greater than the correlation with sleep length, they found that social jetlag more greatly increased the likelihood that a person was overweight.

In fact, people who were socially jetlagged, which means they were unable to go to sleep and wake up when their natural circadian rhythms would tell them to, were more than three times more likely to be overweight.

"Overall, our results indicated that sleep timing is an equally important predictor for BMI as is sleep duration," they wrote.

They state that sleep timing has shifted later in industrialized countries and therefore become "incompatible with traditional work times."

"It is as though the majority of the population is working the early shift," they write. "Here, we identify this discrepancy between biological and social timing as one of the many factors contributing to the epidemic of overweight and obesity."

According to William Kohler, MD, the director of the Florida Sleep Institute in Spring Hill, Florida, the work of Roenneberg's team provides more evidence for the link between sleeping problems and weight gain, a trend already well documented in research.

"This is another way of looking at why sleep deprivation in all its forms can contribute to obesity," Dr. Kohler said. "The misalignment of the social clock and the circadian clocks that causes insufficient sleep is another mechanism for obesity."

He said many people, if not most, fall into that category of having an internal clock misaligned with the clock they have to adhere to in society because of their work or other commitments.

"There's not a good solution," he said. "Getting the manufacturers and different businesses to adjust to a different time for work would be hard."

The best a person can do is try as much as possible to choose work and leisure activities that, as much as is possible, allow them to go to sleep when they are naturally tired and wake up when they are naturally ready to.

Sleeping aids such as melatonin, available over the counter, may aid some people in adjusting their schedules but should be used under the care of a doctor.

The study appeared online May 10 in the journal Current Biology. The research was funded by the European Commission, the Netherlands Organization for Scientific Research, the University of Groningen Rosalind Franklin Program, and the Hersenstichting Nederland. No conflicts of interest were noted.

Review Date: 
May 8, 2012