A long-haul flight can take us to the other side of the world in just a few hours. However, our bodies don’t automatically adjust to this change. For example, someone flying from Europe to New York arrives about six hours “earlier” than their internal clock indicates. On a flight from Singapore to New York, the difference is as much as about eleven hours.
The problem isn’t just the time difference. The real issue is chronobiology.
What exactly is jet lag?
In short: Jet lag occurs when your internal biological clock is not (yet) synchronized with the sunrise and sunset times in your destination country.
Our bodies have a complex circadian system that regulates numerous processes over the course of approximately 24 hours: sleep and wakefulness, body temperature, hormone release, metabolism, physical performance, and much more.
This genetically encoded internal clock has a free-running rhythm of about 23.5 to 25 hours within the population and synchronizes, among other things, with the day-night cycle to our 24-hour cycle. During the flight, the body essentially carries the time zone of the departure location with it until we disembark at our destination. At that point, the body’s internal clock no longer matches the time at the destination. So we might be lying in bed at the hotel at 11 p.m. local time—while our body is possibly still set to 5 p.m. Or we might have to get up at 7 a.m., even though our internal clock is still in the middle of the biological night.
This discrepancy is exactly what jet lag is.
Typical symptoms include sleep problems, daytime sleepiness, difficulty concentrating, reduced performance, changes in appetite, and a general feeling of being “out of sync.”
There is an important chronobiological rule to keep in mind:
Jet lag isn’t equally difficult to cope with in every direction.
Traveling east is generally more difficult for the body’s internal clock than traveling west. The reason: The human circadian clock usually adapts more easily to a longer day than to a shorter one.
The Three Worst Routes for Jet Lag
A recent analysis by booking.com for Business, which was also reported on by BILD, reveals some remarkable findings regarding the most extreme long-haul routes.
1. Singapore → New York
Time difference: 11 hours
2. Hong Kong → Boston
Time difference: about 11 hours
3. Hong Kong → New York
There’s also a time difference of about 11 hours.
The analysis indicates a potential adjustment period of approximately 11 days for these connections. But… nature doesn’t operate on a schedule, so this figure shouldn’t be taken as an exact biological rule. How long it actually takes a person to adjust depends, among other things, on the direction of travel, light exposure, sleep patterns, chronotype, age, individual adaptability, and the specific travel situation. So jet lag isn’t just a matter of the number of time zones you’ve flown through.
The Five Most Important Steps to Combat Jet Lag
1. Adjust your body clock before your flight
When dealing with an extreme time difference, it’s a good idea not to wait until you arrive at your destination to start adjusting. You can gradually shift your bedtime and wake-up time to match the local time a few days before your trip. The goal isn’t to overcome the entire time difference while you’re still at home. The goal is to reduce the amount of adjustment needed after arrival.
Especially when it comes to vacations, you should take the length of your stay into account. If you spend two-thirds of your time just dealing with jet lag, the vacation has failed to serve its purpose of relaxation.
2. Use light strategically
When it comes to shifting our internal clock, light is the most important timing cue. But: A lot of light isn’t automatically good light. The timing is what matters.
Morning light can shift the body clock in a different direction than evening light. That’s why the same light source can have a completely different effect depending on your biological clock. If you want to reduce jet lag, you shouldn’t simply try to get as much daylight as possible; instead, you should ask yourself: When does my body clock need light, and when should I avoid it?
3. Take a Strategic Approach to Sleeping on a Plane
The biggest mistake is to plan your sleep during the flight based solely on the idea that “I have to sleep as much as possible.”
What matters much more is when this sleep occurs. For example, sleeping for several hours at a time when the body should already be preparing for the biological night at the destination can help with adjustment. Conversely, sleeping according to the local time at the departure location can make adjustment more difficult. Sleep is therefore not just a matter of the amount of sleep when it comes to jet lag.
Timing is everything.
After landing, consistently follow the local time
The body needs orientation.
Therefore, upon arrival, the most important timekeeping devices should be set to the new local time as soon as possible:
- Light
- Sleep
- Meals
- Exercise
- social activities
For example, if you arrive at 3:00 p.m. local time and immediately go to bed in a dark hotel room for several hours, you may end up achieving the exact opposite of what you actually want. That doesn’t mean you have to force yourself to stay awake after a 15-hour flight.
But a long “restful nap” at the wrong time can make falling asleep at night much more difficult. However, people who struggle with naps in particular should try to see how long they can stay awake. Knowing your own chronotype can also help here. Because on vacation, in particular, two things come together:
- Jet lag
- The genetic sleep-wake cycle, which suddenly no longer recognizes an alarm clock. If you know your biological chronotype, you can adjust to your new surroundings even faster once you arrive at your destination… provided the alarm clock doesn’t become a fixture there, too.
Don’t Overestimate the First Few Days
When there is an extreme time difference, you can’t simply reset your internal clock through willpower alone. While you can function according to local time, that doesn’t mean your entire body is already operating on local time.
That is why, on extremely long-distance trips, you should—if possible—avoid planning activities that require maximum cognitive or physical exertion during the first few days. The combination of jet lag, sleep deprivation, and activities where mistakes can have serious consequences is particularly problematic.
The body is already in the process of adapting. We shouldn’t make it any harder on itself.
What happens to the chronotype after arrival?
This is where it gets really interesting. Many people imagine their internal clock to be like a wristwatch: set it to the new local time—and you’re done.
That’s not how our circadian system works. Your chronotype doesn’t change just because you travel. A person who is a pronounced “night owl” doesn’t suddenly become a “morning person” just because they fly from Frankfurt to New York.
A figurative comparison: Anyone who boards a completely darkened airplane in Germany initially carries their German rhythm with them. If they were to arrive in New York and then spend an extended period of time in the darkened plane, their genetic rhythm would slowly stabilize … depending on their genetic predisposition, between 23.5 and 25 hours. Only when they step off the plane and come into contact with the sun’s path in New York does the internal clock receive the signal: “This isn’t what I just had,” and it tries to adapt to the local daily rhythm. This then manifests as “jet lag.” BUT… I bring my chronotype with me. So if I get tired at 10:00 p.m. in Germany, I’ll also get tired at that time in New York after the jet lag has worn off—as long as an alarm clock doesn’t interfere. Two other factors also influence this:
- The location of a place of stay within a time zone can vary by up to 60 minutes.
- Some countries also have artificial time zones, such as China with Beijing Time, or Spain, which has followed the German time zone since World War II instead of using its own.
Sleep, hormones, body temperature, metabolism, and other rhythms can adapt to the new time at different rates. This means that you may already feel “adjusted” even though your internal clock hasn’t fully adjusted yet. And that’s exactly why jet lag can still be present even when you seem to be sleeping normally again, which is why you should wait a little longer if you have a job that involves risks.
It also gets interesting when different chronotypes are involved.
A pronounced “night owl” generally has a different circadian rhythm than a “morning person.” That’s why the same trip with an identical time difference can be more or less taxing for two different people. However, a long “restful sleep” at the wrong time can make it much harder to fall asleep at night. However, especially those who struggle with “naps” should try to see how long they can stay awake. Knowing your own chronotype can also help here. Because, especially on vacation, two things come into play:
- Jet lag
- The genetic sleep-wake cycle, which suddenly no longer recognizes an alarm clock. If you know your biological chronotype, you can sync up even faster once you reach your destination… provided the alarm clock doesn’t become a regular part of your routine there, too.
That’s why jet lag is more than just a lack of sleep
A long-haul flight doesn’t just take us to a different place geographically. It throws our body clock off balance. And that’s exactly why it’s not enough to combat jet lag with sleep alone. If you want to adjust your internal clock to the new local time as quickly as possible, you need, above all, to make proper use of the most important external cues.
Light. Sleep. Exercise. Nutrition. Daily routine.
