Interrupted sleep, irritability, disorientation, lack of motivation -- these are only a few of jet lag's symptoms, and even the most seasoned travelers experience them to some degree when venturing across time zones.

Despite opinions to the contrary, the biggest cause of jet lag is not the number of hours traveled, but the time zones. Experts say that changing time zones throws off the body's circadian rhythms, which control the release of hormones and chemicals that let you know when to eat, sleep and wake up.

In Pictures: How to Beat Jet Lag

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"Most processes within our bodies are regulated by a 24-hour timing mechanism or clock that can be called our 'biological clock,'" says Chris Colwell, a professor in psychiatry at the UCLA Medical School. "Rapid travel between time zones temporarily disrupts this biological clock and results in the set of symptoms known as jet lag." Because the body's clock can only adjust gradually, a little each day, adjusting to a new environment can be a slow process. "Our system does readjust but this takes time," Colwell says. "It can take a couple of weeks to adjust to the new time in Europe or Asia."

The direction of travel also plays a role in the severity of jet lag. Traveling east is harder than traveling west, says Colwell. "The reasons why are a little complicated, but, in essence, it is easier for us to delay our clock than to speed it up."

According to a 1999 article in the Journal of Sport Behavior, eastward travel is more difficult because it compresses days into shorter time periods, taking a person further from the body's natural rhythms. Westward travel, by comparison, expands days to more closely correlate with the body's internal cycle.

In addition to sleep disorders, complications from jet lag can include swollen limbs, gastrointestinal problems, dehydration and even memory loss. A 1994 New Zealand [Images] survey of international flight attendants found that while they were used to long-haul travel, 90 percent suffered from tiredness over the first five days of arrival; 94 percent experienced a lack of energy and motivation; 93 percent reported broken sleep; and 70 percent had ear, nose or throat problems.

In Pictures: How to Beat Jet Lag

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Despite the prevalence of jet lag, a few simple tricks can help you minimize its irritating impact on your holiday. The first and most obvious thing you can do, according to Colwell, is to accept that jet lag will play a role in your vacation and plan accordingly.

"Be self-aware and recognize that you will not be at your best for a number of days following a long trip. You may find cognitive processes like memory impacted," he says. On the airplane, Colwell recommends staying hydrated, stretching often and going light on the alcohol. Once you arrive in the new time zone, he says, "expose yourself to sunlight and social interactions. The worst thing is to go into a dimly lit hotel room and watch TV."

Pre-travel preparations are important, too. Andrew Criglington, the inventor of "No-Jet-Lag" and CEO of Miers Laboratories, a New Zealand company that designs and markets homeopathic preparations, says "too much excitement, stress and disorganization" can worsen your symptoms. Some research suggests that jet lag may also be reduced by taking supplements and natural remedies. Since plane travel is known to interfere with the body's production of melatonin, a hormone that helps regulate circadian rhythms, taking a supplement may help you adjust to new sleeping patterns. "Some people are helped by melatonin (0.5mg dose) before bed in the new time zone," says professor Chris Colwell. But he notes, "While approved as sleeping aids, these drugs have not yet been approved for jet lag."

Indeed, a paper documenting the incidence of jet lag on the cabin crew of a commercial airline published in 2004 by the Indian Journal of Aerospace Medicine found that melatonin delays the circadian rhythms when taken in the morning and advances them when administered in the evening. As such, melatonin may enhance the quality of sleep you get, or worsen it -- depending on when it's taken. If you choose to go this route, be sure to follow the directions.

Exercise and diet may also affect the severity of your jet lag. While exercise itself has little direct effect on adjusting the body's biological clock, experts say that moderate physical training leads to an increase in sleep length and nighttime alertness. Try to exercise a few hours before bedtime or engage in aerobic activities immediately after waking up to get the best results. As for your diet, Colwell recommends eating light meals at regular times in the new time zone so as not to stress your digestive system. "Recognize that your whole digestive system is tightly coupled to this biological clock and takes many days to readjust," he says. Try fasting before travel, avoiding food on the plane if possible, then eating as soon as you land.

Perhaps the most conflicting advice received when suffering from jet lag is whether or not to take a nap once you arrive at your destination. Colwell says that taking a nap can indeed help the body deal with jet lag, but only if you limit it to 30 or 40 minutes. The worst thing you can do is hop into bed the minute you arrive and stay there for hours. "A long nap can confuse your biological clock and make the readjustment to the new time zone worse," he warns.

In Pictures: How to Beat Jet Lag

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