If you’ve ever traveled across time zones, you’ve likely experienced what chronobiologists call circadian disruption.
Jet lag leaves you more than just tired. You’re hungry for a turkey dinner with all the trimmings in the middle of the morning, you can’t keep from nodding off at 4 in the afternoon, and you find yourself wide awake in the middle of the night with no hope of sleep. Your brain grasps what the clock on the wall says, but your body’s peripheral clocks (organs with their own circadian rhythms) are completely confused as a result of the flight. Your pancreas thinks it’s still in London, your liver is stalled over Greenland, while your kidneys know you’re back home in Akron.
Jet lag is an example of acute circadian disruption. Your body can’t tell if it’s night or day, so it doesn’t know whether to wind down for sleep or wake up for breakfast.
Still, you don’t need to fly around the world to experience out-of-sync body clocks. Many of us are in a state of chronic circadian disruption.
A disruption occurs anytime we get too little or poor-quality sleep. It’s even provoked by slight day-to-day shifts in bedtimes and wake times — like hanging out with friends late on the weekend, then sleeping in the next day (a phenomenon dubbed “social jet lag”).
The effects of circadian rhythms on our health are critical, and not just because of their role in helping us fall asleep and wake up. When our internal clocks get out of sync, our health and well-being do, too.
Chronic circadian disruption is linked to poor concentration and memory, diminished performance, increased risk-taking behavior, and problematic detoxification. Circadian misalignment is also associated with mood and anxiety disorders, as well as a range of other acute and chronic health concerns. (See “Circadian Rhythms and Gene Expression,” below.)
“Circadian health is important because it is closely linked to both physical and mental health,” says Phyllis C. Zee, MD, PhD, a professor of neurology at Northwestern University who specializes in sleep and circadian medicine. “There’s a preponderance of evidence that when your circadian rhythms are misaligned, it can be a risk factor for chronic conditions like diabetes, heart disease, obesity, and cancer.”
A 2012 Danish study, for example, found that women who work the night shift are up to four times more likely to develop breast cancer. The landmark Nurses’ Health Study II (1989–2007) found that women who worked rotating night shifts for 20 years or more had a 44 percent increased risk for type 2 diabetes.
Not surprisingly, the key to circadian alignment is adequate sleep — but getting more of it is only part of the equation. Sleep quality also matters, as do sleep timing, food timing, and light exposure.
Which is why, instead of just another pill, many sleep experts now prescribe a whole host of lifestyle strategies to help restore good sleep habits and align your body’s rhythms.
Your Internal Clocks
The body’s master clock is a group of cells in the brain’s hypothalamus called the suprachiasmatic nucleus, or SCN. Zee describes the SCN as the “circadian pacemaker” in the brain. It’s located right above the optic nerve and responds to 24-hour cycles of light and dark, which it uses to help orchestrate the body’s many rhythmic functions. This is the same part of the brain that regulates certain hormones (cortisol, insulin, and melatonin) and energy (glucose).
The body is also home to several individual peripheral clocks that live in such organs as the pancreas, liver, kidneys, heart, gastrointestinal (GI) tract, muscle tissue, adipose tissue, and breast tissue. These clocks respond to instructions from the SCN for a range of functions, including hormone production and digestion. The entire body operates according to rhythmic schedules, not just our sleep and wake cycles.
“These rhythms are generated at a cellular level in single cells,” Zee explains. “Every cell in your body contains the molecular machinery to generate these 24-hour rhythms.”
The system works like an orchestra, with the SCN as the conductor and the peripheral clocks as the musicians. Each instrument can be played at its own tempo, but if musicians did this during a performance, the orchestra would sound cacophonous. To make music, each follows the conductor and stays on beat.
When our circadian rhythms are aligned, the body acts like a well-tuned orchestra — a state of circadian alignment known as entrainment. When we’re entrained, Zee says, we’re better able to predict our best times for eating, activity, and performance. Our sleep and wake times naturally become more regular, and we feel better overall. (To gauge how well you’re sleeping, see “How to Measure Your Sleep Satisfaction,” below.)
When the peripheral clocks are out of sync with the SCN, however, disruption takes the form of different physiological messages that compete for your attention. For example, if it’s 11 p.m. and your SCN sends out signals to prep for bed, but your GI tract believes it’s noon and tells you it’s time for lunch, you’ll have a harder time falling asleep because you’re thinking about a sandwich.
“Ideally, your metabolic systems are ready to eat when you’re awake, whereas they’re turning all that down when you’re sleeping,” says Zee.
Any of the physiological rhythms can get off track, she explains. If the rhythmic secretion of melatonin or cortisol (triggered by signals from the hypothalamus, where the SCN is housed) gets out of whack, it can create physiological confusion about when to be active and when to rest.
A strong urge to nap during the day or sleeplessness at 2 a.m. are both signs of circadian disruption. (For more on cortisol’s effects, see “The Cortisol Curve“.)
The most common causes of circadian disharmony are inappropriate and insufficient light exposure, as well as irregular sleep: too much, too little, or at the wrong time. This soon becomes a self-perpetuating cycle, Zee says, because exposure to natural light and dark “are the strongest synchronizing agents” for the circadian system.
“The SCN is very sensitive to light as well as to melatonin,” she explains. This is why bright light at night is particularly disruptive to our circadian rhythms. The SCN requires stimulation from daylight to stay on track and signal the peripheral clocks at the appropriate times.
“The best entraining solution is exposure to light during the day and having the unopposed ability [through darkness] to elevate your melatonin at night,” Zee says.
Darkness allows the pineal gland to produce this soothing hormone. Exposure to bright light at night -disrupts this process and makes it harder to fall asleep.
Likewise, bright light stimulates the SCN through the optic nerve, which prompts your body’s clocks to assume their daytime roles. Zee notes that even people who are blind may not be “circadian blind”; their SCN is still able to respond to bright light.
“The core message here is that you need to have enough, appropriately timed, and sufficient sleep, as well as light exposure,” she adds.
How to Get the Best Rest
To align your internal clocks and ensure deep, restorative sleep, Pay attention to these three key factors.
1. Sleep Timing
Keeping a consistent sleep and wake time is one of the best ways to synchronize your body clocks, says Aviva Romm, MD, a functional physician and herbalist with a practice in New York City. “A lot of people are very disregulated in both, and having them tightly controlled is really important.”
This means sticking to the same sleep hours every day of the week — even weekends. Deviating about half an hour on either side is fine. But that’s it, no matter how tempting it is to stay up until 3 a.m. on Sunday and sleep until brunch.
A consistent wake-up time is the most critical element for circadian health, says Ft. Myers, Fla.–based functional-medicine practitioner José Colón, MD, MPH, author of The Sleep Diet: A Novel Approach to Insomnia. And he believes it should be on the early side.
“I see it all the time with my patients,” he says. “I ask about when in their lives they got the best sleep and they will say ‘when I was in the military’ or ‘when I was at summer camp.’ It’s that early wake-up time.”
Colón advises not sleeping past 7 a.m. An early-rising routine helps ensure that melatonin will naturally start to rise around 8 or 9 p.m., which helps you grow sleepier in time to knock off by 11 p.m.
If you’re not able to maintain consistent sleep and wake times, and feel tired during the day, Colón suggests avoiding lengthy midday naps — anything more than 40 minutes is probably too long. This is because the brain uses glucose for energy and creates a waste product called adenosine, which builds up during the day and causes us to start feeling drowsy. Long naps purge adenosine too early in the day, so come evening, the sleepy feeling never arrives.
Napping for less than 40 minutes, however, will boost your daytime vitality without disrupting your nighttime sleep, says Colón. So cat naps — or a little longer — are still OK.
2. Food Timing
Zee recommends finishing your evening meal at least two to three hours before bedtime. Because late hours and low light trigger the SCN to signal the peripheral clock in the GI tract to shut down metabolic activity, the body is less equipped to break down food at night. This is one of the reasons night-shift work can lead to health complications.
“In night-shift work, people are eating at night, which makes sense, but their bodies never completely adjust,” says Daniel Buysse, MD, a University of Pittsburgh professor of sleep medicine. Even if someone is accustomed to being awake at night, the digestive and metabolic systems perceive this as an “adverse circadian time,” so night-shift meals are harder for the body to process. “That in itself may contribute to the weight gain and obesity that is often associated with night-shift work,” he explains.
And when we eat late at night, we tend to make more indulgent food choices. Many researchers in social psychology have posited that willpower is a limited resource that gets depleted during the course of a day. This may be why a cupcake seems to have a more mystical power over us after dark.
“No one craves a salad at 11 p.m.,” says Zee. “We know that if you’re sleep deprived you’re more likely to want to eat carbs and make unhealthy food choices.” Sweet carbs are a source of quick energy — just the kind of thing you crave when deciding to stay up late and finish that expense report.
Sleep experts also recommend avoiding alcohol right before bed. Drinking may reduce the time it takes to fall asleep, but it tends to delay the onset of REM sleep, which studies have shown can translate into less restful sleep overall. If you’re going to imbibe, limit it to one drink with dinner, at least three hours before bed. That gives your body time to process the alcohol well before lights-out.
If you notice that even a little alcohol with dinner disrupts your sleep, pour a bit of tart cherry juice in your wineglass instead of wine, advises Colón. It contains a small amount of melatonin.
3. Light Exposure
Exposure to light and dark is a critical — and often-overlooked — component of circadian health.
Bright natural or natural-mimicking light during the day helps regulate melatonin production. You don’t need to be exposed for long periods of time, says Zee: A morning stroll with your dog, a bike or car commute to work, eating lunch outside, even making sure your office space is brightly lit all help.
Sunglasses protect your eyes, but wearing them constantly can reduce melatonin production, Colón warns. (If your eyes are never exposed to bright light, the onset of darkness won’t trigger the pineal gland to produce the hormone.) Take off your shades in the morning light to reset your sleep–wake cycle.
Receiving bright light in the morning is another reason an early wake-up time is so important, he adds. Stimulating blue-wavelength light, which is strongest in the morning, has the most powerful effect on the circadian cycle because the receptors in our retinas are most sensitive to it, and they transmit these stronger signals to the SCN. (In the late afternoon, we see more red- and orange-wavelength light, which is less stimulating.)
Blue light after dark can be a surprisingly powerful sleep disrupter. “One of the biggest things we know that affects sleep is using any kind of electronics before bedtime,” says Romm. Blue light is produced by computer, phone, and tablet screens, as well as energy-efficient light bulbs — and most of us read screens by lamplight well after the sun sets.
Direct eye-to-screen exposure up to the very moment we go to bed, such as checking email on smartphones and reading on tablets as we nod off, puts us at odds with our natural rhythms.
“The circadian system evolved expecting that our days would be more or less filled with light and activity, and our nights would be filled with darkness and much less activity,” says Buysse. “We need to be careful of all the temptations of the modern world that lead us away from a regular 24-hour cycle.”
Romm recommends powering down all screens in the evenings at least an hour before bed. If that’s not feasible, try an app that dims blue light on smartphones, tablets, and computers, such as f.lux for Apple or Twilight for Android.
Either way, keep lamps on their lowest setting after dinner, and consider getting a red light bulb for the bedroom. Not only does it look romantic, but the brain associates red-spectrum light with the end of the day and the waning of sunlight.
Sleep Like a Baby
Creating a better environment for sleep isn’t difficult: Remove electronics from the bedroom, get some light-blocking curtains, and develop relaxing prebedtime habits, like a warm bath and a cup of herbal tea. Restorative rituals send a signal to your body clocks about what’s coming next — sleep — so they can all align.
Think of a baby. You wouldn’t just plop her in front of a tablet until bedtime and then put her straight into the crib. She gets a bath, a lullaby, a bottle, some cuddles. Find the things that calm you as an adult and treat yourself in the same loving way.
Your well-rested body will thank you.
How to Measure Your Sleep Satisfaction
The most common measure of quality sleep is duration, or, colloquially, how many hours you get each night. Restoring the circadian cycle, however, requires a broader definition of a good night’s rest, so a team of researchers at the University of Pittsburgh created one: the acronym RU-SATED.
“The acronym lets us look at the individual dimensions of sleep, and also allows us to consider them in the aggregate,” says professor of sleep medicine Daniel Buysse, MD. Each letter stands for a critical component of healthy sleep.
RU is for regularity, or going to bed and waking up at about the same times every day.
S is for sleep quality. Do you make it into deep sleep or toss and turn all night?
A is for alertness, or how rested and alert you feel after a night’s sleep.
T is for timing. “Most studies of adults find that the midpoint of their sleep should be somewhere between 2 and 4 a.m., so if your timing is different than that, that may lead to increased health risks,” says Buysse.
E is for efficiency, the ability to fall asleep and stay asleep for a consolidated period, and not waking up multiple times in the middle of the night. Many experts now believe that even waking up to go to the bathroom might have nothing to do with our bladders: It can happen when our cortisol spikes at the wrong time, or because our circadian clocks are out of sync.
D is for duration, or how many consecutive hours of sleep you get during the night.
Buysse says we can measure our sleep-related health risks by how much success or trouble we have with each of the above. How hard is it for you to keep a regular sleep-and-wake time? Do you sleep deeply or restlessly? Are you alert or groggy when you first get up? Buysse suggests you add up the categories in which you have issues. The greater the number of problem areas, the greater the risks for sleep-related health problems compared with someone who has issues in only one or two.