Jet lag, also called jet lag disorder, is a temporary sleep problem that can affect anyone who quickly travels across several time zones.
Your body has its own internal clock, called circadian rhythms. They signal to your body when to stay awake and when to sleep.
Jet lag occurs because your body's internal clock is synced to your original time zone. It hasn't changed to the time zone of where you've traveled. The more time zones crossed, the more likely you are to experience jet lag.
Jet lag can cause daytime fatigue, an unwell feeling, trouble staying alert and stomach problems. Although symptoms are temporary, they can affect your comfort while on vacation or during a business trip. But you can take steps to help prevent or lessen the effects of jet lag.
Symptoms of jet lag can vary. You may experience only one symptom or you may have many. Jet lag symptoms may include:
- Sleep problems such as not being able to fall asleep or waking up early.
- Daytime fatigue.
- Not being able to focus or function at your usual level.
- Stomach problems such as constipation or diarrhea.
- A general feeling of not being well.
- Mood changes.
Symptoms are worse the farther you travel
Jet lag symptoms usually occur within a day or two after traveling across at least two time zones. Symptoms are likely to be worse or last longer the farther you travel. This is especially true if you fly east. It usually takes about a day to recover for each time zone crossed.
When to see a doctor
Jet lag is temporary. But if you travel often and experience jet lag, you may benefit from seeing a sleep specialist.
A disruption to your circadian rhythms
Jet lag can occur anytime you cross two or more time zones. Crossing multiple time zones puts your internal clock out of sync with the time in your new locale. Your internal clock, also called circadian rhythms, regulates your sleep-wake cycle.
For example, if you leave New York on a flight at 4 p.m. on Tuesday and arrive in Paris at 7 a.m. Wednesday, your internal clock still thinks it's 1 a.m. That means you're ready for bed just as Parisians are waking up.
It takes a few days for your body to adjust. In the meantime, your sleep-wake cycle and other body functions such as hunger and bowel habits remain out of step with the rest of Paris.
The effect of sunlight
A key influence on circadian rhythms is sunlight. Light affects the regulation of melatonin, a hormone that helps cells throughout the body work together.
Cells in the tissue at the back of the eye transmit light signals to an area of the brain called the hypothalamus. When the light is low at night, the hypothalamus signals to a small organ in the brain called the pineal gland to release melatonin. During daylight hours, the opposite occurs. The pineal gland releases very little melatonin.
Because light is so crucial to your internal clock, you may be able to ease your adjustment to a new time zone by exposing yourself to daylight. However, the timing of light needs to be done properly.
Airline cabin pressure and atmosphere
Some research shows that changes in cabin pressure and high altitudes associated with air travel may contribute to some symptoms of jet lag, regardless of travel across time zones.
In addition, humidity levels are low in planes. If you don't drink enough water during your flight, you can get slightly dehydrated. Dehydration also may contribute to some symptoms of jet lag.
Factors that increase the likelihood you'll experience jet lag include:
- Number of time zones crossed. The more time zones you cross, the more likely you are to feel jet lag.
- Flying east. You may find it harder to fly east, when you "lose" time, than to fly west, when you "gain" time.
- Being a frequent flyer. Pilots, flight attendants and business travelers are most likely to experience jet lag.
- Being an older adult. Older adults may need more time to recover from jet lag.
Auto accidents caused by drowsy driving may be more likely in people who are jet-lagged.
A few basic steps may help prevent jet lag or reduce its effects:
- Arrive early. If you have an important meeting or other event that requires you to be in top form, try to arrive a few days early to give your body a chance to adjust.
- Get plenty of rest before your trip. Starting out sleep deprived makes jet lag worse.
- Gradually adjust your schedule before you leave. If you're traveling east, try going to bed one hour earlier each night for a few days before your trip. If you're flying west, go to bed one hour later for several nights before you fly. If possible, eat meals closer to the time you'll be eating them during your trip.
Properly time bright light exposure. Light exposure is a prime influence on your body's circadian rhythms. After traveling west, expose yourself to light in the evening to help you adjust to a later than usual time zone. After traveling east, expose yourself to morning light to adapt to an earlier time zone.
The one exception is if you've traveled across more than eight time zones. Your body might mistake early-morning light for evening dusk. It also might mistake evening light for early-morning light.
So if you've traveled more than eight time zones to the east, wear sunglasses and avoid bright light in the morning. Then allow as much sunlight as possible in the late afternoon for the first few days in your new location.
If you've traveled west by more than eight time zones, avoid sunlight a few hours before dark for the first few days to adjust to the local time.
- Stay on your new schedule. Set your watch or phone to the new time before you leave. Once you reach your destination, try not to sleep until the local nighttime, no matter how tired you are. Try to time your meals with local mealtimes too.
- Stay hydrated. Drink plenty of water before, during and after your flight to counteract the effects of dry cabin air. Dehydration can make jet lag symptoms worse. Avoid alcohol and caffeine, as these can dehydrate you and affect your sleep.
- Try to sleep on the plane if it's nighttime at your destination. Earplugs, headphones and eye masks can help block noise and light. If it's daytime where you're going, resist the urge to sleep.