Jet lag

DEFINITION

Jet lag, also called jet lag disorder, is a temporary sleep disorder that can affect anyone who quickly travels across multiple time zones. Jet lag is caused when your body’s internal clock or circadian rhythms, which tell your body when to stay awake and when to sleep in the old time zone, are out of sync with cues from the new time zone, such as light exposure and dining times. The more time zones crossed, the more likely you are to experience jet lag.

Jet lag can cause daytime fatigue, an unwell feeling, difficulty staying alert and gastrointestinal problems. Jet lag is temporary, but it can significantly reduce your vacation or business travel comfort. Fortunately, there are steps you can take to help prevent or minimize jet lag.

CAUSES

A disruption to your circadian rhythms

Jet lag can occur anytime you cross two or more time zones. Jet lag occurs because crossing multiple time zones puts your internal clock or circadian rhythms, which regulate your sleep-wake cycle, out of sync with the time in your new locale.

For example, you lose six hours on a usual New York to Paris flight. That means that if you leave New York at 4:00 p.m. on Tuesday, you arrive in Paris at 7:00 a.m. Wednesday. According to your internal clock, it’s 1:00 a.m., and you’re ready for bed, just as Parisians are waking up.

And because it takes a few days for your body to adjust, your sleep-wake cycle, along with most other body functions, such as hunger and bowel habits, remains out of step with the rest of Paris.

The influence of sunlight

A key influence on your internal clock is sunlight. That’s because light influences the regulation of melatonin, which in turn is a synchronizing signal to cells throughout the body.

Certain cells in the tissue at the back of your eye (retina) transmit the signal of light to an area of your brain called the hypothalamus. At night, when this signal is low, the hypothalamus tells the pineal gland, a small organ situated in the brain, to release the hormone melatonin. During the day, the light signals to the hypothalamus result in the opposite, such that the pineal gland produces very little melatonin.

You may be able to ease your adjustment to your new time zone by exposing yourself to daylight in the new time zone so long as the timing of light is 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.

Not drinking enough water during your flight can dehydrate you. In addition, drinking too many beverages with caffeine or alcohol during your flight can affect your sleep and cause some symptoms of jet lag.

SYMPTOMS

Symptoms of jet lag can vary. You may experience only one symptom or multiple symptoms. Jet lag symptoms may include:

• Disturbed sleep — such as insomnia, early waking or excessive sleepiness
• Daytime fatigue
• Difficulty concentrating or functioning at your usual level
• Stomach problems, constipation or diarrhea
• A general feeling of not being well
• Muscle soreness
• Menstrual symptoms in women

Symptoms worse the farther you travel

Jet lag symptoms usually occur within a day or two of travel if you’ve traveled across at least two time zones. Symptoms are likely to be worse or last longer the more time zones that you’ve crossed, especially if you travel in an easterly direction. It’s estimated to take about a day to recover for each time zone crossed.

When to see a doctor

Jet lag is temporary. But if you are a frequent traveler and continually struggle with jet lag, you may benefit from seeing a sleep specialist.