 Jet lag is a blessing to circadian biologists because the disruption of mental and physical well-being immediately highlights the importance of their work, the study of our internal body clock. Much of the general malaise we may experience on long journeys may just be so-called travel fatigue, which can occur regardless of the time zone, leaving people feeling disoriented, generally weary, headache-y. Dehydration has been blamed. The air circulating the cabins of commercial airlines is pretty dry, yet it can make your throat, skin, and eyes feel dry. But if you do the math, the maximum loss of fluid through like breath and sweat wouldn't be more than like an extra half cup. So it's not like you're in Death Valley or something, and that calculation assumes that the passenger would be nude, and I'm sure they charge extra for that. Of course, giving people salty pretzels doesn't help. The vegetarian option tends to be healthier if they're serving meals, but you have to specify that when you book. BYOF, bring your own fruit, is a good rule, to fly by, or unsalted nuts as a snack. The cabin air isn't just dry, but low in oxygen pressure, about what you'd get 10,000 feet above sea level, like twice as high as Denver, and that alone can make you feel not so great. Even when you land, if you've crossed enough time zones, you can suffer from jet lag, which is the temporary disconnect between the new time at your destination and that of your own internal body clock, which is still on home time. This is abnormal, since our internal clock is normally synced to the outside world, but the symptoms of jet lag go away as our body becomes hip to the new time. This usually takes, in days, two-thirds of the number of time zones crossed eastwards, compared with half the number of time zones crossed westwards. So London is like six time zones east away from Chicago, so flying there may take four days before you're back to normal, whereas Londoners flying to Chicago should get over their jet lag in only three days. The reason it's easier to go west, where the day is longer than east, is because our internal clock is naturally set for longer than 24 hours, and has to be reset every day. That's why they call the daily rhythm surcadian, meaning about a day. In fact, you can see this in major league baseball performance. Research has churned through 40,000 games, mining 20 seasons, and found surprisingly specific results of circadian misalignment, jet lag. And indeed, the problems arose most after eastward travel, with very limited effects after westward travel, consistent with the greater than 24-hour cycle length of the human circadian clock. OK, but how do you treat it? First, you need to figure out if it needs treating at all. If you're just traveling one or two time zones, you don't have to worry about it. If you're crossing three or more time zones, like traveling coast to coast, it then depends on how long you plan on staying. If it's just a few days, it's probably not worth treating it, since then you'll have to switch back as soon as you get back home. If you have control over your schedule, it's better to time appointments in the new time zone to coincide with daytime back home. So it's pretty much common sense. If you travel east, your body will still think it should be sleeping in the morning, so you should push stuff later and vice versa. But if you're going to be gone a while, you can adjust your body clock using behavioral methods and or drug supplements or foods. There's only one sure-fire way to avoid jet-life altogether and that's to adapt to the new time zone before your trip. However, changing your home sleep schedule more than a few hours can be counterproductive by interfering with your pre-trip sleep and you don't want to be going into a long trip already sleep-deprived. Before your trip, you want to maximize your sleep. In-flight, the recommendation is to immediately adjust to the destination meal schedule, easier said than done. And then once you land, you want to try to maintain the destination sleep schedule. Try not to nap more than a few minutes and you don't want to be driving around when your body thinks it's the middle of the night. But the key to treating jet lag is light therapy. Going east, you expose yourself to bright light in the morning and avoid bright light in the evening and vice versa going west. But it's more complicated than that. The advice switches if you're traveling through more than six time zones because your biological clock may then adjust in the wrong direction. And it's even more complicated than that. The effects of light acting upon the body clock is only actually during a specific window around the time your body temperature bottoms out. This is usually around 4 a.m. You drop from 98.6 down to like 97.6, even when you're not sleeping. It's just part of our circadian rhythm. The bottom line is here are the two cheat sheets. You can take a snapshot of for future reference. So, for example, if you fly from LA to London, eight time zones east, you would avoid light between 6 a.m. and noon local time and expose yourself to light between noon and 6 p.m. local. And the rest of the day, it doesn't matter, it won't affect you either way. Okay, now, but that's just on day one. On subsequent days, the local times of light avoidance and exposure need to be advanced earlier by 1 to 2 hours each day until light avoidance coincides with when you're sleeping. But on those first few days after traveling east, you'll note you're going to want to be avoiding morning light, which can be difficult if that's when your flight gets in. One thing you can do is wear really dark glasses until you get indoors, but if they're too dark, you can't really drive. So that's where these kind of ugly orange lenses that block blue wavelengths can come in handy. Preventing the dip in melatonin, you get just wearing regular sunglasses. Regardless, the next day, I know there's the urge to get out and about, but that could actually make your jet lag worse by taking you in the opposite direction. What about if you're flying more than 8 time zones east? Then you subtract the number from 24 and treat it as travel west. So a 10 time zone trip to the east, like New York to Delhi, should be treated as a westward flight, requiring a delay in your body clock across 14 time zones. In that case, it would be easy to get outside and get some sun, but if you just went four time zones west and need to get light in the middle of the night, what do you do? A gadget company came up with like light emitting headphones, the theory being you could bathe your brain and light directly through the ear canals. They stuck them in the heads of cadavers and did seem to get some light penetration, but you don't know until you put it to the test. This randomized double blind placebo control trial demonstrated that transcranial bright light exposure via the ear canals could alleviate jet lag symptoms or you could just turn on a lamp.