Jet lag is a temporary sleep disorder that occurs when we rapidly cross multiple time zones. The body’s circadian rhythm — our “body clock” that controls biological functions such as when we eat and sleep — gets disrupted when we experience daylight and darkness at the “wrong” times in a new destination.

Anyone who has traveled across several time zones will recognize the symptoms: disturbed sleep, daytime fatigue, difficulty concentrating, headaches and irritability. Gastrointestinal disturbances include indigestion, constipation or diarrhea and a decreased interest in eating. Some travelers experience increased reactions to alcohol, a general unwell feeling, muscle soreness and, for women, menstrual symptoms.

Many factors exacerbate the effects of jet lag, including long periods of sitting, oxygen deficiency and aircraft cabin conditions such as decreased pressure, warm temperature and low humidity. According to a July 2007 study published in the New England Journal of Medicine, simulated air travel at cabin pressures equal to 7,000 to 8,000 feet of altitude produced symptoms of malaise, muscular discomfort and fatigue. Most airline cabins circulate very dry air which can be dehydrating; mild dehydration is associated with feelings of illness, headache and eye and nasal discomfort.

Jet lag effects can vary based on the direction of travel: poor sleep or delayed onset of sleep after eastward travel, early awakening after westward flight and disturbed sleep after flights in either direction. Flying east is more difficult due to the loss of time; flying west allows you to gain time back.

Symptoms can last from one to several days depending on the number of time zones crossed and your ability to adapt. They usually do not require medical treatment. If you are a frequent traveler who is bothered by jet lag, you may need a prescription medication to help you sleep during the flight or for a few nights at your destination, though there may be side effects such as nausea, vomiting, sleepwalking, confusion and morning sleepiness. Medications may aid you in sleep but cannot reduce daytime symptoms of jet lag.

While we cannot eliminate jet lag, we can learn to lessen its effects. Individuals respond differently to long-distance travel and in their ability to adapt to new time zones. The intensity and duration of jet lag are related to the number of time zones crossed, the direction of travel, the ability to sleep while traveling and the availability and intensity of local circadian stimuli such as light and darkness at the destination. Your exposure to local natural light-dark cycles usually accelerates adaptation after jet travel over two to 10 time zones.

Natural sunlight is the most powerful tool for regulating the sleep-wake cycle. The pineal gland in the brain influences circadian rhythms by responding to light and dark. The retina transmits light signals to the hypothalamus, which sends them to the pineal gland. At night, the pineal gland releases the sleep-producing hormone melatonin. During the day, melatonin production is very low.

Light therapy using natural sunlight or artificial light can ease the transition to a new time zone. Some travelers alter their diets, eating protein to stay awake and carbohydrates to sleep. Supplemental melatonin has been studied as a sleep aid and jet lag remedy but remains controversial; ask your doctor if it is right for you. Anyone taking melatonin should avoid alcohol. Melatonin’s side effects include dizziness, headache, loss of appetite, nausea and disorientation.

There are things you can do before your departure that will greatly influence your jet lag experience. When scheduling a trip, opt for layovers rather than non-stop flights when crossing four or more time zones. Try to arrive several days early so you can adjust to the new tIf you’ll be traveling east to west, go to bed later and wake up later several days before your departure. If traveling west to east, go to bed earlier and wake up earlier. Gradually adjust meals to the new time zone and drink plenty of fluids. Avoid or minimize alcohol and caffeine use. Try to avoid tension or stress before departure.

During your flight, breathe deeply and walk about the cabin whenever possible. Also exercise at your seat: Roll your feet, raise your knees, turn your head, raise your arms overhead and contract and relax your leg muscles. Use eye drops to counteract dry cabin air. If it is nighttime at your destination while you are traveling, sleep on the plane with the aid of ear plugs, eye shades and headphones. If it is daytime at your destination, avoid sleeping on the plane. Avoid heavy meals, alcohol and caffeine in flight.

At your destination, adjust immediately to the activities of the time zone. Get sunlight as soon as possible, sleep at the normal time for that zone and avoid naps. Maintain a regular sleep and exercise schedule. Eat only food that you are used to at first and drink plenty of clear bottled water.

Time Travel Tools

Jet Lag Relief: It’s About Time by Daryal Mark

Jet lag calculators for trip-specific advice:
British Airways
Fleet Street Clinic
Lumie Light Therapy

The content of this article is for informational purposes only. It is not intended to be a substitute for professional medical advice, diagnosis or treatment. Always seek the advice of your physician or other qualified health care provider with any questions you may have regarding a medical condition.ime zone before a major event.