Jet lag: the main killer of productivity and enjoyment when travelling across time zones. Common folk remedies include pressure points, aromatherapy, and light exposure behind the knee. But is there evidence any of these actually work? Probably not. Fortunately, recent research on circadian rhythms has suggested a reliable method to reduce or even completely prevent jet lag.
Circadian rhythms are the roughly 24-hour biological rhythms that drive changes within humans and most other organisms. For example, humans have circadian rhythms of alertness and body temperature. Usually these rhythms align with the environment’s natural light and dark cycle: peak drowsiness occurs around 5:00 AM, when it is often dark out. Jet lag occurs when our rhythms no longer align with the environment. Flying from Vancouver to Moscow — 12 hours ahead — means that peak drowsiness occurs at 5:00 PM, when one would usually want to be alert. Although scientists have known about circadian rhythms for centuries, evidence has recently accumulated that we can apply this knowledge to minimise the negative effects of shift work and jet lag.
Whether circadian rhythms align with the environment is determined by factors such as exercise, melatonin, and light. Bright light exposure is the most powerful way to cause a phase shift — an advance or delay in circadian rhythms. Light in the early morning makes you wake up earlier (“phase advance”); light around bed time makes you wake up later (“phase delay”).
This simple insight can be used to minimise jet lag. For example, Helen Burgess and colleagues from the Rush University Medical Center in Chicago studied whether jet lag could be prevented by phase shifting before departing. After three days of light exposure in the morning, the participants’ circadian rhythms shifted by an average of 2.1 hours. This means they would feel less jet lagged, and would be fully adjusted to the new time zone around two days earlier. Several field studies have reached similar conclusions.
Thus, seeking and avoiding light at the right times can reduce jet lag. To seek light, expose yourself to bright and continuous light by going out in sunlight or using a commercially-available portable light box. To avoid light, stay indoors away from sunlight, or wear dark sunglasses.
Calculating when to seek and avoid light depends on the number of time zones crossed, direction of travel, and usual wake and sleep times. These calculations can be done automatically online, or manually by following some rough guidelines:
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.
Of course, most people try to adjust to the new time zone without controlling their exposure to light and dark. These people often end up jet lagged for longer than necessary. They can also experience antidromic re-entrainment, when the circadian rhythms shift in the opposite direction. For example, incidental light exposure can cause people to phase delay rather than phase advance, making jet lag worse. Besides gastrointestinal disturbances and reduced alertness, frequent jet lag is associated with cancer and digestive diseases in humans, and increases mortality in mice.
Given this knowledge of circadian rhythms, one can — as one article title claimed — “trick Mother Nature” into letting you fly around the world without jet lag. And you won’t even need a flashlight behind your knee.
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