Jet Lag

Some Helpful Jet-Lag Rules

Whether you’re a tourist or an expat frequent-flyer, jetting across multiple time zones can take its toll. Different people react differently, but no one can completely escape the physical and mental effects of jet lag.


Passengers board a United Airlines 747 aircraft for a flight from San Francisco (SFO) to Frankfurt (FRA).
PHOTO © Hyde Flippo

Note that the title of this article is not “Avoiding Jet Lag.” The only way to avoid jet lag is to stay at home and not fly across more than one time zone (or fly only in a north-south direction). When you fly across several time zones you will suffer to some degree from desynchronosis, more commonly known as jet lag. It’s a law of nature that humans avoided until the age of flight. Little did the Wright brothers know what they had wrought! But it was not until more speedy passenger jetliners became common that air travelers really began to experience what came to be known as jet lag.

When the body’s internal clock gets “out of sync” by being transported into a distant time zone, without adequate time to adjust its circadian rhythms, we suffer from jet lag. Flying across up to two time zones is usually not a problem for most people, but crossing the six to nine time zones between Europe and North America can be.

In research on circadian rhythms the German noun “Zeitgeber” (“time giver” or synchronizer) is used to refer to external factors that influence the body’s internal clock. The most important zeitgeber, for plants and animals, is light. The term zeitgeber came into English in the 1960s.

And what are the impacts of jet lag? They include the following: problems with sleeping, reduced mental acuity, difficulty communicating, fatigue, irritability, memory lapses, a diminished level of concentration and increased susceptibility to disease. Research has shown that the average person’s productivity and performance after a long flight can drop by as much as 20 percent, mostly due to a lack of sleep. Sleep disorder is jet lag’s number one symptom.

A jet lag rule of thumb says it normally takes one day per time zone to get back to “normal” (flying west to east). That means, after a nine-hour time change on a flight from the US west coast to Germany, you’ll need nine days before your body fully adjusts to Central European Time. Of course you’ll be able to function fairly normally before that, but a common indicator that your circadian rhythms aren’t quite back to normal is becoming sleepy in the early afternoon. One study claims it only takes two-thirds of a day per zone, or about six days to adjust to a nine-hour time difference (west to east).

For westward flights, it is somewhat easier to adjust to the time zone shift, only requiring about half a day per time zone. For most people that means only about four days to adjust to a nine-hour time difference after flying east to west. So your jet lag will be milder for a flight from Frankfurt to San Francisco than going the other way. For some reason the body has an easier time adjusting to gaining daylight (by flying westward) rather than losing it (by flying eastward).

What Doesn’t Work?
Contrary to folk wisdom, scientific studies have yet to establish with any certainty that common, supposed jet-lag remedies actually work. Claims that a high-carbohydrate or Argonne diet, aromatherapy or doses of melatonin will combat jet lag have never been substantiated scientifically. The only “drug” definitely known to help with jet lag is good old-fashioned caffeine (for alertness). Unfortunately, there is still no real cure or preventative for jet lag!

What’s Your Chronotype?
Another factor in jet lag is your “chronotype.” There seem to be three types of people with three different chronotypes. Type one is a person who has very few problems coping with jet lag. Type two has about average difficulty adjusting to a new time zone. The third type has great difficulty adjusting. Older people (60+) tend to have less regular circadian rhythms, and thus more trouble coping with jet lag. Young children usually have less difficulty with jet lag. No matter which chronotype you are, the rules below can help you better cope with jet lag.

SEVEN RULES for Alleviating Jet Lag

1. No Alcohol
The number one recommendation from most jet-lag experts is to avoid drinking any alcohol during your flight. Alcohol has at least two negative effects: (a) It dehydrates the body, which is something you don’t want, and (b) it is a sedative that can cause poor performance and sleep problems after your flight arrives. It may be tempting to drink a little wine or a cocktail to relax, but that temporary benefit is just that, temporary. In the long run you’ll be better off by avoiding anything alcoholic. Even after you arrive, it’s a good idea to be moderate in your consumption of alcohol, especially for the first few days.

2. Don’t Sleep During the Flight – or Do
Sleep on the plane only if it is the normal sleep time for your destination. Some people have difficulty sleeping on a plane at all, but it’s a good idea under certain conditions. If your flight will arrive during the day and you’ll have at least six to eight hours before it’s time to go to bed in the new time zone, then catching some shut-eye is a good idea. (To help you sleep, bring a sleep mask, earplugs and a blow-up pillow or neck rest. Movie time is a good bedtime on the plane.) But if your flight arrives at night, you should stay awake in the air. Some people like to work or otherwise stay active during the flight, so they’ll be ready to sleep at night after arriving in the new time zone.

3. Hydrate
The typical jetliner’s cabin environment is similar to being at the top of an 8,000 ft mountain with very dry air – for six hours or more. You need to drink water and other non-alcoholic beverages at regular intervals during your flight. That’s why the flight attendants serve drinks fairly often. Avoid coffee unless you plan to remain active.

4. Fly in Business or First Class
Yeah, right. But seriously, getting out of cramped coach accommodations will help you feel much better during your flight and after you arrive. It’s definitely better for getting some sleep (if you should). Get an upgrade if you can!

5. Walk Around During the Flight
Yes, no more gathering around the toilets, and all that. But you can and should get out of your seat from time to time on a long flight. You can also do simple stretching exercises in your seat. A little exercise goes a long way.

Air Travel
Flying to and from Germany/Europe, or within Europe

6. Exposure to Bright Light (or Avoiding It)
Exposure to sunlight or bright artificial light has been shown to influence circadian rhythms. However, the time and length of the exposure is important. Exposure to bright light at the wrong time of day or night can worsen the effects of jet lag, rather than alleviate them. Avoiding light exposure can be just as important as getting it. (Some travelers even wear sunglasses on the plane!) Based on trials, the timing for light exposure can be complicated, so we recommend it only in a general way. (A good time for light exposure is usually in the afternoon in the new time zone; avoid light in the morning. See the British Airways Jet Lag Calculator for details.) The idea is to realign your internal clock to daylight and darkness in the new time zone. Get outdoors in the afternoon.

7. Immediately Adjust to Your New Time Zone’s Day or Night
If your flight arrives in Frankfurt at 10:00 a.m. local time, don’t go to sleep! (See Rule 2 about sleeping or not sleeping on the plane!) You probably can’t check in at your hotel until after 2:00 p.m. anyway. Stay active and resist the temptation to take a nap! If you lay down, you may wake up in the middle of your new night. Get outside and be active!

On the other hand, if your flight arrives at night or near bedtime in your arrival city, you should try to get a good night’s sleep. The key here is to avoid fighting your new time zone. The sooner you adapt to your new daytime or nighttime, the better off you’ll be. Some people set their watch to the arrival time zone as soon as the flight takes off.

Tip: Try to arrive at least a day ahead of any important business meeting to avoid problems due to jet lag.

The many studies on melatonin as a treatment for jet lag have produced conflicting results. (Light exposure/avoidance seems to have a stronger effect on the body’s sleep cycle.) But if you want to use melatonin to alleviate jet lag, be aware of its limitations and side effects.

Next | Air Travel

Related Pages


  • “Jet lag: Trends and coping strategies” (PDF) –, Vol. 369 (March 31, 2007) – The Lancet now requires payment for downloading the PDF file
  • Overcoming Jet Lag from Brian’s Guide to Getting Around Germany
  • A Battle Plan for Jet Lag – The New York Times
  • Jet Lag – CDC – A guide to jet lag from the Centers for Disease Control and Prevention (CDC)

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