Jet lag can be debilitating, especially if you travel long distances. It can cut into your much-needed vacation, or dull your wits when you have to attend, or speak at, a conference. It can leave you with a headache, lethargy, irritability and the inability to focus and concentrate on tasks.

Dr. Katherine Green knows. She travels a lot. Sometimes for fun, but often in her role as Medical Director of the Sleep Center at the University of Colorado Hospital or as Assistant Professor and Director of Sleep Surgery at the University of Colorado School of Medicine.

“With jet lag, the No. 1 thing most people notice is the disruption of sleep patterns,” she said. “Basically, it’s the disruption of being in sync with the time zone you are in now versus the time zone where your body thinks it is (where you live). It’s a disruption of the circadian rhythm.” And, she added, it can affect not only sleep, but your appetite, your hormones and more.

Its severity is directly related to how many time zones you cross, she said.

“Most people can tolerate crossing a time zone or two without being really affected, but if you cross more than that, it can be difficult not to be impacted at least a little bit,” Green said.

Some people “power through” the time change when they hit the ground at their destination, and if you can do that, it can be an effective way to cope, she added.

“It’s not a bad strategy. The faster your body can adapt to the time zone you are in, the better off you will be.’’

In general, jet lag is worse traveling eastward. “It is easier for your body to adjust to gaining time than it is to adjust to losing time.”

She suggests using “plane time” effectively to prepare your schedule beforehand.

If your plane leaves at 10 a.m. local time but that is 9 p.m. where you are going, sleeping on the plane (as if you were leaving at 9 p.m.) can be very helpful, she said.

“If traveling somewhere for vacation or pleasure, you can adjust at a more leisurely pace than if you are traveling for work or business. Then you have to make the transition quicker, and it can be hard.”

If traveling really far, almost a full day, it’s almost easier to adjust than if just doing 12 hours, she added.

How can we pre-empt it?

“If you have the ability, be cognizant of the time zone you’re getting into, and try adjusting your schedule to it even a few days ahead of time,” she suggested. Go to bed earlier or later, relative to the time zone you’ll be visiting. Eat meals on, or at least closer to, the new time zone’s schedule.

Have trouble sleeping on planes? Many people do.

“Ask your doctor for a sleep aid,” she suggested. She doesn’t usually recommend over-the-counter sleep aids. “In general, if you’re taking a sleep aid, be sure to have a 7-to-8-hour window to get that sleep, especially on international flights. Don’t take a sleep aid if you don’t have a sufficient amount of sleep time – or you’ll be groggy.”

If, despite your preparations and best efforts, jet lag does kick in, you can minimize the symptoms by staying hydrated and avoiding alcohol “which tends to disrupt sleep quality any time, but also can have a negative impact on jet lag.”

In general, she said, “the best thing you can do is try to adjust to the time zone you are in as quickly as you can. Even if you are tired during the day, try not to take long naps. If you get there and are not tired but it’s night, take a sleeping aid for the first few days.”

There are naturopathic ways to fight jet lag, Green said.

Melatonin is one of the few over-the-counter supplements she does recommend.

“Melatonin is a natural hormone that your body produces to help regulate the sleep cycle, and can be a good supplement to take to counteract jet lag,” she said.

Taking it within an hour or so of bedtime can trigger the body to produce its own (melatonin) and help you sleep. It’s really a strong driver of your sleep cycle,” she said. “There’s good evidence that its reputation is well founded.”

She’s used it herself, but admits she is not often affected much by jet lag.

“My own clock apparently is not too sensitive,’’ she said. “Some people are more sensitive to (time changes) than others.”

What works best for her, personally, is to “try to make sure of getting into the new time zone in my head and making that adjustment in advance.”

Light therapy also can help.

“Sunlight stimulates your body clock to be in its “wake” time, so getting natural light within an hour after you wake can be another way to help your body adjust,” she said.

And for short pleasure trips – like a long weekend maybe – over just a few time zones, she said she often does not try to adjust at all. So you go to bed at 8 instead of 11, or get up at 10 instead of 7, and eat meals at odd times (for the zone you’re in). So what?

“Just stay on your own sleep-wake cycle,” she advised.

After all, a lot of restaurants serve breakfast all day, and that’s why they make “Do Not Disturb” signs for hotel rooms.