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What causes jetlag?
There are two things that people commonly refer to as "Jetlag".
One of these is just travel fatigue. Travel fatigue comes from sitting sedentarily in the dry air of an aircraft for 10 or more hours, not getting enough excercise, fluids, or sleep. Travel fatigue may make you feel tired when you get to your destination, but travel fatique is not the same as jetlag.
True jetlag, properly called desynchronization, is when your body's natural clock is out of synch with the local time.
Everybody has in internal clock that adjusts the body's functions over time during the day. During the day, this internal clock increases your pulse rate, your respiration, and your metabolism, making you feel wide awake and energetic. It increases your mental accuity. At night, it decreases all these functions, making it easier to sleep.
To understand the difference, imagine that you flew from NY City to Lima Peru. The flight takes 10 hours, but ends up in the same time zone. You would certainly feel travel fatigue, but you would not experience desynchronization. You would still be ready for bed in late evening and awake at 10 o'clock in the morning.
Now imagine that Scotty could beam you to Paris instantaneously. You wouldn't have travel fatigue, but you would certainly have desynchronization. At 10 PM Paris time, your internal clock would think it was early afternoon, and, instead of being ready to settle down to sleep, you would be wide awake. After a sleepless night, you would drag yourself out of bed at midnight (your time) and try to endure a day that feels like the middle of the night.
On the first morning of my first trip to Europe, my co-worker and I were sitting on a bench in a hospital hallway, waiting to go in a talk to a doctor. Out of boredom I took my pulse rate. As I remember, it was around 40-50. I remarked to my co-worker, "We're asleep; we just don't know it."
So, what can you do about it?
The "remedies" that most people cite for jetlag - getting enough sleep before your trip, sleeping on the plane, avoiding too much alcohol - will help against travel fatigue, but they do nothing to fight desynchonization. Mind you, they might make you feel a little better, and thus jetlag won't bother you as much, but they won't actually reset your biological clock.
One of the least effective "remedies", in my opinion, is the old saw that you should force yourself to stay awake until your normal bedtime over there. That doesn't reset your clock. I have actually found that a short, one or two hour nap before dinner refreshes me and helps me get through the rest of the evening.
Your internal clock is constantly being synched by sunlight. No one's clock runs on an exactly 24 hours schedule. Some of us, night people, run on a longer schedule (25 hrs?), so we are never quite ready to call it a day, and when we do go to bed, we aren't ready to get up. Morning people, on the other hand, are always running ahead of schedule, up at the crack of dawn and crashing early in the evening.
I saw a documentary over 30 years ago where the put people in deep mineshafts, where there was no sunshine, not ever temperature variations. The had no clocks, just lights that they could turn off when they wanted to go to sleep and turn on when they wanted to be asleep. The researcher found that the people tended to be on an approximate 24 hours schedule, but some got constantly ahead while others fell constantly behind.
If nothing modulated our clocks, pretty soon the morning people would get ahead by 12 hours and the night people would get behind by 12 hours, and we both would be on the same schedule (up all night and sleeping all day). Why doesn't that happen? What keeps out clocks sychronized to day- and night-time?
The answer is sunshine. Sunshine on our skin produces a chemical, melanonine, that keeps our clocks in synch.
So, if you want to reset your clock in Europe, get out in the sun when your body expects dark. In Europe, that means getting out, and on the go, in the morning.