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jet lag==倒时差 方面的具体信息  

2013-06-25 03:00:25|  分类: 医学进展新干线 |  标签: |举报 |字号 订阅

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What is jet lag?

Jet lag, also called desynchronosis and flight fatigue, is a temporary disorder that causes fatigue, insomnia, and other symptoms as a result of air travel across time zones. It is considered a circadian rhythm sleep disorder, which is a disruption of the internal body clock.


What are other symptoms and signs of jet lag?

Besides fatigue and insomnia, a jet lag sufferer may experience a number of physical and emotional symptoms including anxiety, constipation, diarrhea, confusion, dehydration, headache, irritability, nausea, sweating, coordination problems, dizziness, and even memory loss. Some individuals report additional symptoms, such as heartbeat irregularities and increased susceptibility to illness.

Children can also suffer the same jet lag symptoms as adults.


What is a time zone?

A time zone is a geographical region which has the same time everywhere within it. The world has 24 time zones, one for each hour in the day. Each zone runs from north to south in strips that are approximately 1,000 miles (1,600 kilometers) wide. (The actual width of each zone varies to accommodate political and geographical boundaries.) As the earth rotates, dawn occurs at a set hour in one time zone, then an hour later in the time zone immediately to the west and so on through the 24-hour cycle. Thus, in the U.S., when it is 6 a.m. in the eastern time zone, it is 5 a.m. in the central zone, 4 a.m. in the mountain zone, and 3 a.m. in the Pacific zone.

Why does jet lag occur?

The cause of jet lag is the inability of the body of a traveler to immediately adjust to the time in a different zone. Thus, when a New Yorker arrives in Paris at midnight Paris time, his or her body continues to operate on New York time. As the body struggles to cope with the new schedule, temporary insomnia, fatigue, irritability, and an impaired ability to concentrate may set in. The changed bathroom schedule may cause constipation or diarrhea, and the brain may become confused and disoriented as it attempts to juggle schedules.


How does the body keep time?

Our bodies have a sort of internal biological clock that follows a 24-hour cycle, called a circadian rhythm. A tiny part of the brain called the hypothalamus acts like an alarm clock to activate various body functions such as hunger, thirst, and sleep. It also regulates body temperature, blood pressure, and the level of hormones and glucose in the bloodstream. To help the body tell the time of day, fibers in the optic nerve of the eye transmit perceptions of light and darkness to a timekeeping center within the hypothalamus. Thus, when the eye of an air traveler perceives dawn or dusk many hours earlier or later than usual, the hypothalamus may trigger activities that the rest of the body is not ready for, and jet lag occurs.


What is the role of melatonin in jet lag?

Melatonin is a hormone that plays a key role in body rhythms and jet lag. After the sun sets, the eyes perceive darkness and alert the hypothalamus to begin releasing melatonin, which promotes sleep. Conversely, when the eyes perceive sunlight, they tell the hypothalamus to withhold melatonin production. However, the hypothalamus cannot readjust its schedule instantly; it takes several days.

Does the direction of travel matter?

Yes. Travelers flying north or south in the same time zone typically experience the fewest problems because the time of day always remains the same as in the place where the flight originated. These travelers may experience discomfort, but this usually results from confinement in an airplane for a long time or from differences in climate, culture, and diet at the destination location. Time differences do not play a role.

Travelers flying east, on the other hand, typically experience the most problems because they "lose" time. For example, on an international flight from Washington, D.C., to Mecca, Saudi Arabia, a traveler loses eight hours. Meals, sleep, bowel habits, and other daily routines are all pushed ahead eight hours.

Travelers flying west "gain" time and usually have an easier time adjusting than eastward travelers. However, they too experience symptoms of jet lag after landing because they still must adjust to a different schedule.


Do the symptoms of jet lag vary in intensity?

Yes. People flying across only one or two time zones may be able to adjust without noticeable effects of the time change. Those flying across three or more time zones will likely develop noticeable symptoms of jet lag. Generally, the intensity of symptoms varies in relation to the number of time zones crossed and the direction of travel. People also vary in their susceptibility to jet lag symptoms and the severity of the symptoms.


How long does jet lag last?

Recovering from jet lag depends on the number of time zones crossed while traveling. In general, the body will adjust to the new time zone at the rate of one or two time zones per day. For example, if you crossed six time zones, the body will typically adjust to this time change in three to five days.

What are the best ways to cope with jet lag?

There are several home remedies that can help with prevention of jet lag and easier recovery from the symptoms. The following are 12 tips to help travelers to avoid or to minimize the effects of jet lag.

Tip 1: Stay in shape

If you are in good physical condition, stay that way. In other words, long before you embark, continue to exercise, eat right, and get plenty of rest. Your physical stamina and conditioning will enable you to cope better after you land. If you are not physically fit, or have a poor diet, begin shaping up and eating right several weeks before your trip.

Tip 2: Get medical advice 

If you have a medical condition that requires monitoring (such as diabetes or heart disease), consult your physician well in advance of your departure to plan a coping strategy that includes medication schedules and doctor's appointments, if necessary, in the destination time zone.

Tip 3: Change your schedule 

If your stay in the destination time zone will last more than a few days, begin adjusting your body to the new time zone before you leave. For example, if you are traveling from the U.S. to Europe for a one-month vacation, set your daily routine back an hour or more three to four weeks before departure. Then, set it back another hour the following week and the week after that. Easing into the new schedule gradually in familiar surroundings will save your body the shock of adjusting all at once.

If you are traveling east, try going to sleep earlier and getting up and out into the early morning sun. If traveling west, try to get at least an hour's worth of sunlight as soon as possible after reaching your destination.

Tip 4: Avoid alcohol 

Do not drink alcoholic beverages the day before your flight, during your flight, or the day after your flight. These beverages can cause dehydration, disrupt sleeping schedules, and trigger nausea and general discomfort.

Tip 5: Avoid caffeine 

Likewise, do not drink caffeinated beverages before, during, or just after the flight. Caffeine can also cause dehydration and disrupt sleeping schedules. What's more, caffeine can jangle your nerves and intensify any travel anxiety you may already be feeling.

Tip 6: Drink water 

Drink plenty of water, especially during the flight, to counteract the effects of the dry atmosphere inside the plane. Take your own water aboard the airplane if allowed.

Tip 7: Move around on the plane

While seated during your flight, exercise your legs from time to time. Move them up and down and back and forth. Bend your knees. Stand up and sit down. Every hour or two, get up and walk around. Do not take sleeping pills, and do not nap for more than an hour at a time.

These measures have a twofold purpose. First, they reduce your risk of developing a blood clot in the legs. Research shows that long periods of sitting can slow blood movement in and to the legs, thereby increasing the risk of a clot. The seat is partly to blame. It presses against the veins in the leg, restricting blood flow. Inactivity also plays a role. It decelerates the movement of blood through veins. If a clot forms, it sometimes breaks loose and travels to the lungs (known as pulmonary embolism), lodges in an artery, and inhibits blood flow. The victim may experience pain and breathing problems and cough up blood. If the clot is large, the victim could die. Second, remaining active, even in a small way, revitalizes and refreshes your body, wards off stiffness, and promotes mental and physical acuity which can ease the symptoms of jet lag.

Tip 8: Break up your trip

On long flights traveling across eight, 10, or even 12 time zones, break up your trip, if feasible, with a stay in a city about halfway to your destination. For example, if you are traveling from New York to Bombay, India, schedule a stopover of a few days in Dublin or Paris. (At noon in New York, it is 5 p.m. in Dublin, 6 p.m. in Paris, and 10:30 p.m. in Bombay.)

Tip 9: Wear comfortable shoes and clothes 

On a long trip, how you feel is more important than how you look. Wear comfortable clothes and shoes. Avoid items that pinch, restrict, or chafe. When selecting your trip outfit, keep in mind the climate in your destination time zone. Dress for your destination.

Tip 10: Check your accommodations 

Upon arrival, if you are staying at a hotel, check to see that beds and bathroom facilities are satisfactory and that cooling and heating systems are in good working order. If the room is unsuitable, ask for another.

Tip 11: Adapt to the local schedule 

The sooner you adapt to the local schedule, the quicker your body will adjust. Therefore, if you arrive at noon local time (but 6 a.m. your time), eat lunch, not breakfast. During the day, expose your body to sunlight by taking walks or sitting in outdoor cafés. The sunlight will cue your hypothalamus to reduce the production of sleep-inducing melatonin during the day, thereby initiating the process of resetting your internal clock.

When traveling with children, try to get them on the local schedule as well. When traveling east and you will lose time, try to keep the child awake until the local bedtime. If traveling west when you will gain time, wake your child up at the local time.

Tip 12: Use sleeping medications wisely -- or not at all 

Try to establish sleeping patterns without resorting to pills. However, if you have difficulty sleeping on the first two or three nights, it's OK to take a mild sedative if your physician has prescribed one. But wean yourself off the sedative as soon as possible. Otherwise, it could become habit-forming.

There are also some homeopathic remedies that may be used. A product called No Jet Lag contains homeopathic remedies leopard's bane (Arnica montana), daisy (Bellis perennis), wild chamomile (Matricaria chamomilla), ipecac (Cephalelis ipecacuanha), and club moss (Lycopodium).

Valerian root is an herb that can be used as treatment for insomnia. Do not take valerian with alcohol. It is important to consult your physician before taking these or any other homeopathic or herbal remedy.

Sleep medications are not recommended for children.

Should I take melatonin?

Another option is synthetic melatonin, which is classified in the U.S. as a dietary supplement. A study in the British Medical Journal in 1989 reported that taking synthetic melatonin tablets can help travelers restore normal sleeping patterns. In that study, 20 volunteers traveling back and forth between New Zealand and England took daily doses of either 5 mg of melatonin or a placebo (a blank, or sugar pill) before, during, and after their flights. Those taking melatonin returned to their normal sleep patterns in 2.85 days on average compared with 4.15 days for those taking a placebo.

However, scientists in the U.S. and many other countries are not yet convinced that enough evidence exists to prove the efficacy of over-the-counter (OTC) melatonin tablets. These scientists also point out the following:

1. No information has been compiled on the long-term effects of taking melatonin. 2. No watchdog measures are in place to assure that all OTC melatonin products meet minimum standards.
In 2005, MIT released the results of a meta-analysis of 17 peer-reviewed studies using melatonin. It showed that melatonin was effective in helping people fall asleep at doses of 0.3 mg. Larger doses of melatonin seem to be less effective after only a few days' use.

For the purpose of treating jet lag, it is suggested that a dose between 0.3 mg and 5 mg of melatonin be taken on the first day you travel at the time you will want to go to sleep at your destination. This may be continued at bedtime for a few days once you are at your destination. Melatonin seems to be most effective when crossing five or more time zones, or traveling east.

Be aware that higher doses of melatonin can cause sleepiness, lethargy, confusion, and decreased mental sharpness. Operating motor vehicles or heavy machinery should be avoided after taking your daily dose of melatonin. Consult your health-care provider if you plan on taking melatonin.

REFERENCES:

Breus, Michael J. "How Long Does Jet Lag Last?" WebMD.com. Dec. 14, 2010. <http://answers.webmd.com/answers/1195390/How-long-does-jet-lag-last>.

Herxheimer, A., and K.J. Petrie. "Melatonin for the Prevention and Treatment of Jet Lag." Cochrane Database Syst. Rev. 2 (2002). <http://www.ncbi.nlm.nih.gov/pubmed/12076414>.

"Melatonin and Sleep." National Sleep Foundation. <http://www.sleepfoundation.org/article/sleep-topics/melatonin-and-sleep>.

"Sleep and Circadian Rhythm Disorders." WebMD.com. Mar. 3, 2010. <http://www.webmd.com/sleep-disorders/guide/circadian-rhythm-disorders-cause>.

United States. National Institute of General Medical Sciences. "Circadian Rhythms Fact Sheet." July 2008. <http://www.nigms.nih.gov/Education/Factsheet_CircadianRhythms.htm>.

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