We've long known about the master clock in our brains that helps us maintain a 24-hour sleep-wake cycle.
But in recent years, scientists have made a cool discovery: We have different clocks in virtually every organ of our bodies — from our pancreas to our stomach to our fat cells.
"Yes, there are clocks in all the cells of your body," explains Fred Turek, a circadian scientist at Northwestern University. "It was a discovery that surprised many of us."
We humans are time-keeping machines. And it seems we need regular sleeping and eating schedules to keep all of our clocks in sync.
Studies show that if we mess with the body's natural sleep-wake cycle — say, by working an overnight shift, taking a transatlantic flight or staying up all night with a new baby or puppy — we pay the price.
Our blood pressure goes up, hunger hormones get thrown off and blood sugar control goes south.
We can all recover from an occasional all-nighter, an episode of jet lag or short-term disruptions.
But over time, if living against the clock becomes a way of life, this may set the stage for weight gain and metabolic diseases such as Type 2 diabetes.
"What happens is that you get a total de-synchronization of the clocks within us," Turek says, "which may be underlying the chronic diseases we face in our society today."
So consider what happens, for instance, if we eat late or in the middle of the night. The master clock — which is set by the light-dark cycle — is cuing all other clocks in the body that it's night. Time to rest.
"The clock in the brain is sending signals saying: Do not eat, do not eat!" says Turek.
But when we override this signal and eat anyway, the clock in the pancreas, for instance, has to start releasing insulin to deal with the meal. And, research suggests, this late-night munching may start to reset the clock in the organ. The result? Competing time cues.
"The pancreas is listening to signals related to food intake. But that's out of sync with what the brain is telling it to do," says Turek. "So if we're sending signals to those organs at the wrong time of day — such as eating at the wrong time of day — [we're] upsetting the balance."
And there's accumulating evidence that we may be more sensitive to these timing cues than scientists ever imagined.
Consider, for instance, the results of a weight-loss study that we reported on, which was published in the International Journal of Obesity. Researchers found that the timing of meals can influence how much weight people lose.
"The finding that we had was that people who ate their main meal earlier in the day were much more successful at losing weight," says study author Frank Scheer, a Harvard neuroscientist who directs the Medical Chronobiology Program at Brigham and Women's Hospital.
In fact, early eaters lost 25 percent more weight than later eaters — "a surprisingly large difference," Scheer says. Another study found that eating a big breakfast was more conducive to weight loss, compared with a big dinner — adding to the evidence that the timing of meals is important.
Beyond weight management, there's evidence that the clocks in our bodies — and the timing of our sleeping, eating and activities — play multiple roles in helping us maintain good health. And different systems in the body are programmed to do different tasks at different times.
For instance, doctors have long known that the time of day you take a drug can influence its potency. "If you take a drug at one time of day, it might be much more toxic than another time of day," Turek says. Part of this effect could be that the liver is better at detoxifying at certain times of day.
Turek says his hope is that, down the road, circadian science will be integrated into the practice of medicine.
"We'd like to be in a position where we'd be able to monitor hundreds of different rhythms in your body and see if they're out of sync — and then try to normalize them," Turek says.
Whether — or how quickly — this may happen is hard to say. But what's clear is that the study of the biology of time is exploding.
"What we're doing now in medicine is what Einstein did for physics," says Turek. "He brought time to physics. We're bringing time to biology."
The irony, of course, is that this insight comes at a time when the demands of our 24/7 society mean more and more of us are overriding our internal clocks.
LINDA WERTHEIMER, HOST:
If you needed an alarm clock to wake up this morning, and you're still feeling bleary-eyed, you're in good company. Lots of us are forced to keep schedules that could be making our bodies' internal clocks go haywire. As part of our occasional series Tick-Tock, we are looking at the effects of time on our lives. NPR's Allison Aubrey reports on new evidence of how our 24-7 society may be taking its toll on our health.
ALLISON AUBREY, BYLINE: On a recent morning at about 7:30, when I'd normally be eating breakfast and starting my day, I meet up with the guy across town, Tom Washburn, who's doing just the opposite. He's finishing his workday as an overnight hospital nurse.
TOM WASHBURN: I'm at the end of my shift, and I'm tired (laughter). Yeah, I need to sleep. I'm dying.
AUBREY: The whole pattern of his life is upside down. And he's feeling it. He ate dinner sometime after midnight last night.
WASHBURN: Sometimes my body just doesn't, you know, cooperate, I suppose. And I get tired. I get hungry. I get bloated. Just things just - it feels off.
AUBREY: Now, it's not just shift workers and jetlagged globetrotters who override their natural circadian rhythms. To a lesser extent, it's also all those people who just can't turn off the iPad at night and have to drag themselves out of bed in the morning. Fred Turek is a circadian scientist at Northwestern University.
FRED TUREK: These people are totally out of synchrony. When their body clock is telling them to go to sleep, they have to be awake. And then when they try to go to sleep, their body clock is saying, hey, time to get up.
AUBREY: Now, Turek says we can certainly bounce back from a trans-Atlantic trip or an all-nighter. But when living against the clock becomes a way of life, lots of things go awry. Study show if you mess with the body's sleep-wake cycle, your blood pressure goes up, hunger hormones get thrown off and blood sugar regulation goes south. Over time, Turek says, this may set the stage for metabolic diseases such as diabetes.
TUREK: What happens is that you get a total de-synchronization of the clocks within us, which may be underlying many of the chronic diseases we face in our society today.
AUBREY: Now, notice that Turek says clocks - plural - within us. We've known for a long time about the master clock in our brains that synchronizes our body to the 24-hour light-dark cycle. But in recent years, scientists have made a pretty cool discovery. It turns out that we have different clocks in every organ.
TUREK: Yes. There are clocks in all the cells of your body.
AUBREY: Wow. It's kind of stunning.
TUREK: Yes. That is a discovery that's literally surprised us, I must say.
AUBREY: Turek says, think of all these clocks in our bodies as instruments or players in an orchestra.
TUREK: The idea that the heart has a clock.
AUBREY: Think of it as a drum.
(SOUNDBITE OF DRUM)
AUBREY: And the kidneys?
TUREK: The kidneys have a clock - two clocks, one in each kidney.
AUBREY: Maybe they're the horns.
(SOUNDBITE OF HORNS)
AUBREY: Then there's the pancreas.
TUREK: Oh, yes. The pancreas has a clock.
AUBREY: That's the flute.
(SOUNDBITE OF FLUTE)
AUBREY: Now, the master clock in our brains is like the symphony conductor, keeping all of the players in sync.
TUREK: Once the conductor comes on, everybody's in synchrony, and it sounds beautiful.
(SOUNDBITE OF ORCHESTRA)
TUREK: The idea that your body is functionally - normally when everybody's in synchrony with the master conductor in your brain.
AUBREY: You're sleeping well, eating regularly and feeling good. But what if the clocks get out of sync?
(SOUNDBITE OF DISJOINTED ORCHESTRA)
TUREK: (Laughter) You sound so bad, right?
AUBREY: And, Turek says, something like this may happen in our bodies. So think back to Tom, the overnight nurse. The master clock in his brain, which is set by the 24-hour light-dark cycle, is like the conductor, cueing all the other clocks in the body that it's night. So for example, his digestive organs are not expecting food.
TUREK: The clock in the brain - it is sending signals out. Do not eat. Do not eat.
AUBREY: And this is where things get out of whack.
(SOUNDBITE OF DISJOINTED ORCHESTRA)
AUBREY: Tom has to eat something on his overnight shift. And when he does, research suggests, this meal may reset the clock in his digestive organs. So instead of being in sync with the master clock, the clock in, say, the pancreas, which has to start releasing insulin to deal with the meal, is getting competing time cues.
TUREK: The pancreas is listening to the signals related to food intake, but that's out of synchrony what the brain is telling it to do. So if you are sending signals to those organs at the wrong time of day, such as eating at the wrong time of day, we're upsetting the balance.
AUBREY: Now, it's still early days for circadian science. But there's growing evidence that different organs and systems in the body are programmed to do different things at different times. For instance, doctors have long known that the time of day you take a drug can influence its potency. And Turek says part of this is that the liver may be better at detoxifying at certain times of day.
TUREK: If you take a drug at one time of day, it might be much more toxic than at another time of day.
AUBREY: And consider a recent weight loss study by a circadian scientist at Harvard named Frank Scheer. He found that the timing of meals may influence how much weight people can lose.
FRANK SCHEER: The finding was that people who ate their main meal earlier in the day were much more successful at losing weight
AUBREY: In fact, early eaters lost 25 percent more weight than later eaters.
SCHEER: So quite a surprisingly large difference.
AUBREY: Now, Northwestern's Fred Turek says his hope is that down the road, circadian science will make a big difference to the practice of medicine.
TUREK: We would like to be in a position where we'd be able to monitor hundreds of different rhythms in your body and determine if they're out of synchrony with each other. And then we would try to normalize them.
AUBREY: Now, whether or how quickly this may happen is hard to say. But what is clear is that the study of the biology of time is exploding.
TUREK: What we're doing now in medicine is what Einstein did for physics at the beginning of the last century. He brought time to physics. We are bringing time to biology. That's new.
AUBREY: The irony is this insight comes at a time when the demands of our society means more and more of us may be ignoring our internal clocks. Allison Aubrey, NPR news.
(SOUNDBITE OF ORCHESTRA)
WERTHEIMER: If you're having a hard time imagining all those clocks ticking away inside you, we have an animated explanation at NPR's food blog The Salt. And that is, of course, available at any time of the day or night. Transcript provided by NPR, Copyright NPR.