One Famous Technique That Doesn't Solve Jet-Lag, And One That Does

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Traveling this holiday season? Here's how to prepare your body for the crushing exhaustion that comes from switching time zones.

Photo Credit: Jeff Sheldon | CC0 1.0

Before we look at surefire ways to address travel fatigue, let's look at a myth that, while almost certainly ineffective, is actually kind of instructive about the whole business of jet lag and circadian clocks.

Folksy Flashlights And Circadian Clocks

There's no shortage of folk remedies for jet lag. Take the one about knees and flashlights: There are some who claim that shining light on the backs of your legs can help stave off the ill-effects of switching time zones. It sounds pretty kooky – but the origins of this advice are less folksy than you probably realize.


The roots of the flashlight/knee claim can be traced to a study out of Cornell University, conducted in the late nineties by researchers Scott Campbell and Patricia Murphy.

In their study, Campbell and Murphy reported that delivering carefully scheduled pulses of light to the backs of test subjects' knees – not with a flashlight, but fiber optic pads – could shift the circadian clock that regulates the body's sleep-wake cycle. Your body keeps time in a variety of ways, but perhaps the most basic involves your circadian clock, which tracks a standard Earth day's 24-hour cycle. It's why most of us fall asleep when it's dark, and wake up when it's light.


The backs of knees are rich in blood vessels that lie close to the skin's surface. By bathing them in light, the researchers reasoned, "it might be possible to transmit a timing signal through the blood."


Campbell and Murphy's findings challenged the belief that light can only reset humans' biological clocks via the eyes, and while their surprising observations appeared in the highly esteemed pages of the journal Science, the study was quick to attract criticism. Four years later, the study's findings were formally called into question – again, in the pages of Science:

...circadian clock researchers Kenneth Wright and Charles Czeisler of Harvard Medical School in Boston repeated the experiment, with a few improvements. For instance, Campbell and Murphy had used body temperature as the indicator of circadian phase for all their subjects. But a later study reported that body temperature can be off by as much as 5 hours from circadian phase, so Wright and Czeisler tracked levels of the nighttime hormone melatonin, thought to be a more precise measure. The result, published in the 26 July issue of Science [Ed. note – the study, "Absence of Circadian Phase Resetting in Response to Bright Light Behind the Knees," can be found here], will disappoint jet-setters: Light to the back of the knees did not shift the circadian clock.


Whether you accept the possibility of non-ocular circadian clock regulation or not, the carefully controlled methods that were needed to elicit a circadian benefit in Campbell and Murphy's study – and Wright and Czeisler's failure to replicate those benefits – make one thing abundantly clear: The war against jet lag should not be waged with flashlights.

So what's a traveler to do? The most simple and effective solution still involves light, but it requires some preparation.


Shifting Your Rhythms

If you take away one thing from the dubious flashlight technique, let it be this: Its intended purpose – namely, recalibrating the phase of your circadian rhythms with the day/night cycle of your destination – is grounded in sound science.

Currently, the most effective way to trigger such a "phase shift" is by exposing yourself to, or hiding yourself from, bright light. As far as light sources go, you can go with good old natural sunlight by way of outdoor exposure, or, if you're traveling somewhere more than a couple timezones away, a light box. (The effusively named but excellently rated Verilux HappyLight Delux Sunshine Simulator should do the trick.)


A man, with his light box, who is clearly feeling pretty chuffed about his decision to shift his circadian clock. Via Amazon.

Some of the best research on phase shifting has been conducted by Helen Burgess, director of the biological rhythms research lab at Rush University Medical Center in Chicago. Together with her colleagues, Burgess has demonstrated that exposing or depriving yourself to light in the days preceding a trip can prepare your body to wake up earlier ("phase advance") or later ("phase delay"), according to the day/night cycles of your destination. Supplementing these adjustments with timed doses of melatonin – an over-the-counter supplement shown in some studies to aid in sleep regulation – seemed to help ease these phase shifts. Burgess recently described a plan she used in anticipation of a trip to Egypt in an interview with the Wall Street Journal:

For several days before the trip, Dr. Burgess advanced her bedtime by one hour each night, and got up an hour earlier each morning. She took a low dose of melatonin in the early afternoon to help her reset her body clock. And she sought out bright light in the very early morning, avoiding wearing sunglasses to maximize her exposure, to wake up her body clock.

In Egypt, Dr. Burgess says she had just one morning when it was hard to get up. "Without the preflight shift [in schedule] I could have had jet lag for over a week, pretty much the duration of the trip," she says.


Not committed enough to adjust your bedtime in anticipation of your trip? There are online calculators that can help you determine the timing and duration of light exposure and light avoidance necessary to shift your circadian rhythms, based on things like your direction of travel and your typical sleep/wake times. Or, you can follow these guidelines, adapted by Scientific American from this 2011 publication on resetting circadian clocks:

1. Estimate when your body temperature reaches a minimum. If sleeping 7 or fewer hours per night, assume this is 2 hours before your usual wake time. If sleeping more, assume this is 3 hours before your usual wake time.

2. Determine whether you need to advance or delay your circadian rhythms. If you are flying east (to a later time zone), such as from Los Angeles to New York, you will need to phase advance. Otherwise, if you are flying west, you will need to phase delay.

3. If you need to phase advance, avoid light for 4 hours before your body temperature minimum, and seek light for 4 hours after it. Otherwise, do the opposite.

4. Shift your estimated body temperature minimum by one hour earlier per day if phase advancing, or one and a half hours later per day if phase delaying.


And if you want to get super technical about it, you can try out an app called Entrain. Designed by Olivia Walch and Daniel Forger, mathematicians at the University of Michigan and Yale, respectively, the app uses mathematical models to design custom schedules of light-exposure its creators claim can help you get over get lag in less than half the time you normally would. These claims were substantiated in a recent study, but Forger says that "what real people are doing outside of a sleep lab environment could be very different." To that end, Entrain's creators have made it available to the public free of charge. If you want to help them out, you can opt to send your data and feedback via the app.