It doesn't take a transcontinental flight to end up out of sync with your body clock. It might just be that you stay up too late.
According to German researcher Till Roenneberg, the disconnect between our social calendars and our biological clocks is creating a kind of jet lag — he's dubbed it "social jet lag."
And the consequence? Expanding waistlines. "The larger the discrepancy between social time and what your biological clock tells you to do, the more likely it is you are [overweight or obese]," Roenneberg tells The Salt.
So who's in this category of the socially jet-lagged? If your weekday work schedule is significantly different from your weekend schedule, it could be you we're talking about here.
Say you wake up at the crack of dawn Monday through Friday, but during the weekend you shift your schedule to later wake-up times and later sleep times. Roenneberg says the effect is as if you are switching time zones on the weekend.
If you listen to my story, you'll hear how the theory jells with a bunch of 20-something professionals — who say they generally are up much later on the weekends. None of them were overweight — or sleepy — but perhaps social jet lag catches up with people eventually.
In his paper, published in Current Biology, Roenneberg estimates that for every hour of social jet lag, the risk of being overweight or obese rises about 33 percent.
Whether disrupting your body clock has an effect on your weight — over and above the fact that it reduces the amount of sleep you get — is unclear. But there's certainly a whole body of evidence linking too little sleep to weight problems.
"As sleep researchers, we do believe that there's an intimate relationship between insufficient sleep and the drive to store fat," Dr. Helene Emsellem of the Center for Sleep and Wake Disorders in Chevy Chase, Md., told us.
The connection between poor sleep and higher body weights has been documented in shift workers such as nurses, in mothers of infants, and even in toddlers and teens. In some cases, people do eat more when their schedules are wacky. But Emsellem says it's also possible that something more primitive is at play here.
"Unfortunately, we have caveman's hard-core wiring," Emsellem says, "and insufficient sleep in primitive times was read by the body: Danger, store fat," she says.
Experts say this may be just one of several complicated mechanisms linking sleep and weight, but the important take-home message is this: Get your ZZZZ's!
"We know if people sleep less, even starting in infants, that this leads to a greater risk of obesity," says Dr. Matthew Gillman, director of the Obesity Prevention Program at Harvard Medical School.
Gillman acknowledges that the "sleep longer, sleep better" message is easier said than done. "I guess I'm a big offender, because I got up this morning at 4 a.m. to make a 6 o'clock flight."
Dr. Clete Kushida, a sleep expert at Stanford Sleep Medicine Center, says more studies are needed to investigate the effects of sleep "timing" separately from sleep duration, though the two are inextricably linked. But he says this new study does offer "some evidence" that living "against the clock" is associated with higher BMI (body mass index).
So, in our crazy, go-go society, even the experts who have a hard time living it say it may be wise to start paying more attention to that internal clock.
STEVE INSKEEP, HOST:
On a Tuesday, it's MORNING EDITION from NPR News. I'm Steve Inskeep.
DAVID GREENE, HOST:
And I'm David Greene.
If you were feeling bleary eyed when your alarm went off or when you started our voices this morning, there's a good chance you're not finely attuned to your body's own sleep ques. A new study by German sleep researchers finds that in our 24/7 culture many of us are paying the price for ignoring our internal biological clocks. And as NPR's Allison Aubrey reports, the consequences can be measured in our expanding waistlines.
ALLISON AUBREY, BYLINE: We all know what jet lag is. You fly across time zones. Your internal clock gets confused and all you want to do is eat and sleep at all the wrong times. But think about this. What if the pace and schedule or our everyday lives is leading to the same sort of effect? This is the theory of German researcher Till Roenneberg.
TILL ROENNEBERG: The idea came from sleep logs. We've got hundreds of sleep logs or even thousands of sleep logs.
AUBREY: Roenneberg says when he analyzed people's sleep and wake times, some interesting patterns emerged. People's schedules during the work week were so different from their routines on the weekend that it was as if they had switched time zones. For example, waking up very early Monday to Thursday and more or less going to bed at a regular time. Then on Friday still waking up early but staying up or staying out with friends until the wee hours of Saturday morning.
ROENNEBERG: What these look like if the people would fly on a Friday evening many time zones to the West.
AUBREY: So Saturday morning you wake up three to four hours later than usual. You eat later, maybe brunch at noon instead of breakfast at 7. And you live by a different clock the whole weekend.
ROENNEBERG: We realized that this was a jet lag-like situation.
AUBREY: He's coined the phrase social jet lag, where sleep isn't governed by your biological clock but by your social calendar. I tried out the theory on a group of 20-something professionals who were hanging out together here in Washington, D.C.
KATIE GAMBALI: That definitely applies to my life.
AUBREY: Friends Katie Gambali(ph) and Amanda Zoytland say their weekend schedules are completely different.
GAMBALI: Well, we don't have to wake up as early because we don't have work. So we'll go out even later and then sleep really late.
AUBREY: Katie Gambali says it does seem a little crazy.
GAMBALI: We were actually just discussing this. A lot of the social norms right now involve like going out at a really late hour. And nobody actually goes out until 11 or 12 at night, which I think is bizarre. But if you don't do it you're not going to be out when your friends are out. So it's kind of the culture now to be a night owl.
AUBREY: For now, this schedule works. This gang of friends is fit and vivacious and say they feel they get enough sleep. But Roenneberg says in the long term, living against our biological clocks can catch up with us.
ROENNEBERG: People who suffer from social jet lag hardly ever sleep one night that is according to their sleep needs.
AUBREY: And Roenneberg's research finds this social jet lag is linked to higher body weight.
ROENNEBERG: The larger the discrepancy between the social time and what your biological clock tells you to do, the more likely it is that you are obese.
AUBREY: Whether disrupting your body clock has an effect on your weight over and above the fact it reduces the amount of sleep you get is unclear, but there's certainly a whole body of evidence linking too little sleep to weight problems.
DR. HELENE EMSELLEM: As sleep researchers we do believe that there's an intimate relationship between insufficient sleep and the drive to store fat.
AUBREY: Physician Helene Emsellem directs the Center for Sleep and Wake Disorders in Chevy Chase, Maryland. She says this connection has been documented in shift-workers such as nurses, in teenagers and in mothers of infants. In some cases, people do eat more when their schedules are wacky. But Emsellem says it's also possible that something more primitive is at play here.
EMSELLEM: Unfortunately, we have caveman hard-core wiring and insufficient sleep in primitive times was read by the body: danger, store fat.
AUBREY: Which was our ancestors' best chance of surviving whatever calamity was keeping them awake. And when this happens it seems a hormonal shift takes place, so that instead of burning calories quickly the body tries to store them. Experts say this may be just one of several complicated mechanisms linking sleep and weight. But Dr. Matthew Gillman of Harvard Medical School, who directs an obesity prevention program, says the important take-home message is this:
DR. MATTHEW GILLMAN: We know if people sleep less, even starting in infants, that that leads to a greater risk of obesity.
AUBREY: Gillman acknowledges that the sleep longer, sleep better message is easier to preach than to live by.
GILLMAN: And I guess I'm a big offender, because I got up this morning at 4 o'clock to make a 6 o'clock flight to Washington, D.C.
AUBREY: But in our crazy, go, go society it may be wise to start paying more attention to that internal clock. You definitely have one. And it does not sound like this:
(SOUNDBITE OF ALARM)
AUBREY: Allison Aubrey, NPR News. Transcript provided by NPR, Copyright NPR.