scorecardHow to reset your body clock for daylight-saving time and jet lag, according to science
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How to reset your body clock for daylight-saving time and jet lag, according to science

How to reset your body clock for daylight-saving time and jet lag, according to science
LifeScience5 min read

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Ah, daylight-saving time, that point in the year when - because of what almost seems like a joke by Ben Franklin - we shift our clocks forward an hour.

Not all states or countries observe the time change, but it is nice to suddenly be able to leave work before sunset. The first morning after you've lost an hour of sleep can be rough, though. (There are actually more auto accidents the week after the change.)

Fortunately, science can help.

We all have a natural internal clock of sorts, our circadian rhythm. It's what makes us feel tired when it's time to sleep and wakes us up in the morning, provided we're on some kind of regular schedule. As a species, our clocks have evolved to mostly match the 24-hour natural light/dark schedule (our internal clock is actually a little longer than 24 hours, but gets naturally re-synchronized by environmental cues). Artificial lighting can wreak some havoc on that system, but exposure to light or darkness generally causes our bodies to produce hormones, particularly melatonin, that tell us when we should be alert or asleep. Most of us are drowsiest around 5 a.m.

Our internal clock can be manipulated, however, to help us adjust to a new schedule. Exercise can help shift that clock, and internal melatonin production has an effect as well (though the effects of supplemental melatonin are less clear). But the most effective way to shift that clock is getting exposure to light - from the sun or certain lamps - at the right time.

How to shift your internal clock for daylight-saving time

According to one recent study, the most effective way to reset your schedule so you wake sometime around sunrise and go to sleep soon after sunset is to go camping. Even in the winter, there's enough natural light to shift your internal rhythm.

But if that sounds like too much hassle, there are less planning-intensive methods that work too.

Hiking Switzerland

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Nature will do the trick.

Try to take in some bright sunlight early in the morning for a few days at the time you want to be awake, and avoid light in the evening, making sure you are in a dark environment by bedtime.

"Full spectrum lighting is probably optimal in terms of the management of all these clockwork hormones that direct the complex physiology we have," Dr. Richard Rosen, director of retina services at New York Eye and Ear Infirmary of Mount Sinai and ophthalmology research director at the Icahn School of Medicine, told Business Insider. Even wearing sunglasses when you are trying to get your body into "ready for bed" mode has been shown to work.

Morning exercise may help too, according to some research, though the data on how effective it is at shifting circadian rhythms is not conclusive (late-evening exercise has been shown to push our natural bedtime cues a bit later).

Taking supplemental melatonin, a pill packed with a synthetic version of the natural hormone, for a short period may help instill "bedtime cues" for some people, though other research finds it doesn't have any effect. (Pregnant women and young people should avoid it either way.)

"The quality [of melatonin supplements] is mixed," says Rosen, since they aren't regulated by the FDA.

FILE PHOTO: An American Airlines airplane prepares to land at Jose Marti International Airport in Havana, Cuba September 19, 2015.   REUTERS/Carlos Garcia Rawlins/File Photo

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Dealing with jet lag or night shifts

For bigger schedule shifts (traveling to a new time zone or adjusting to an evening shift at work), more intervention is needed.

Some data shows that using flashing lights - like camera flashes - at carefully defined intervals can shift your schedule. A study published in the Journal of Clinical Investigation found that setting up flashes can establish a new "morning cue" that effectively shifts the body clock.

"If you are flying to New York tomorrow, tonight you use the light therapy. If you normally wake up at 8am, you set the flashing light to go off at 5am," Dr. Jamie Zeitzer, the lead researcher of that study, told The Guardian. "When you get to New York your biological system is already in the process of shifting to East Coast time."

Another effective strategy (that doesn't rely on flashing lights) is to strategically avoid exposing yourself to light, according to research published in the Cleveland Clinic Journal of Medicine.

The researchers created guidelines you can follow on your own, and there's also a website that will do the calculations the researchers recommend for you.

Here's a breakdown of their instructions, with help from an explanation by Scientific American:

  1. Figure out when your body temperature naturally hits a minimum, around when you are drowsiest. If you normally sleep for seven hours or fewer, that point should be around two hours before you wake up. If you sleep longer than that, figure it's around three hours before your alarm.
  2. Generally, if you are flying east, you'll want to advance your circadian rhythm; when you fly west (to an earlier time zone), you'll want to delay that rhythm.
  3. To advance your rhythm, avoid light for three hours before your core temperature hits its minimum and expose yourself to light for at least three hours after that time. To delay your rhythm, you'll do the opposite - expose yourself to light before hitting that core minimum, and staying in the dark for a few hours after.
  4. To shift your core temperature minimum time (when you are drowsiest), start from your home time zone time and change the periods in which you're avoiding and exposing yourself to light day by day. Make that time earlier by one hour each day if you are trying to advance your rhythm. Its easier to delay your circadian rhythm, so you can shift your core temperature time by two hours later each day if you're doing that.

Here's what a chart of that would look like for someone switching their sleep schedule seven hours earlier:


Cleveland Clinic Journal of Medicine

If you have to go eight hours or more forward, researchers say it's easier to simply delay your clock, as if you were flying west. Here's what a shift to a time zone nine hours east would look like:


Cleveland Clinic Journal of Medicine

It's an effective strategy, though the website calculation is perhaps a bit easier than figuring it out on your own.

The best way to adjust your internal clock, however, is simply to get outside as much as possible.

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