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104 wiersze
6.2 KiB
Plaintext
104 wiersze
6.2 KiB
Plaintext
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Jet Lag: Pathophysiology and Cures
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The longest Monday of my life
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I recently returned to the US from Australia. The 14-hour flight took me from Monday morning in Sydney to Monday
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morning, again, in L.A. Crossing the date line messed up my sense of time enough without the added bonus of thinking I
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should be heading to bed just as the sun began to climb into the California sky.
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You may be familiar with the concept: Jet lag. The catch-all name for circadian misalignment, the disruption of sleep
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cycles and circadian rhythms. If you've had the pleasure of crossing time zones in a jet plane, whether it was a mere
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three-hour hop from one coast of the US to the other or a trip to another continent, chances are, you've experienced
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some amount of jet lag.
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The pathophysiology of jet lag
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Normally, two systems--the homeostatic system and the circadian system--work together to produce a 24-hour sleep
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cycle. During the day, the homeostatic system slowly accumulates a 'sleep drive,' a desire to sleep that increases as a
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function of time spent awake. The circadian system generates an alerting signal in opposition to this sleep drive,
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which, during the day, keeps a person from feeling increasingly sleepy. An hour or two before bedtime, this signal
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subsides, and s/he realizes it's time to hit the pillow. The sleep drive dissipates as a person sleeps and by morning
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(assuming a full night's rest and possibly some coffee), s/he will be feeling alert and ready to go again.
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Robert Sack wrote a delightful paper [PDF] on jet lag, by the way, which is
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where I'm getting much of my information.
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So we've got a nice cycle of sleep. Jet lag is what happens when the homeostatic and circadian processes are
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misaligned. For example, the circadian system may signal a person to be alert when it's not actually morning, or may be
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reduced during daytime hours, causing daytime sleepiness because the homeostatic sleep drive is no longer cancelled
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out.
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But I don't want to be sleepy!
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How do you beat jet lag? Robert Sack lists three primary approaches:
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Reset the body clock
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Prescribed sleep scheduling
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Medication to counteract daytime sleepiness or insomnia
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Let's start with the first one, as it turns out to be the most complicated.
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Resetting the body clock
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The two most effective ways to reset the body clock are 1) through bright light exposure, and 2) timed melatonin
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administration.
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Light is one of the most important cues about time of day and has the greatest effect on circadian timing (much
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smaller effects are seen from regular activities and meals, for example). Studies have shown that without light cues,
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totally blind people tend to have free-running circadian
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rhythms with an average period of 24.5 hours, instead of the usual 24. If a person is exposed to bright light early in
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the day, the person's internal clock is reset to an earlier time; if exposure is instead in the evening, the internal
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clock is reset to a later time. Brighter light has more of an effect (such as the sun, at 3000 to 10,000 lux), though
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lower intensities (e.g., 100-550 lux) can produce changes.
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Artificial light sources can be used to supplement daylight, to help reset a person's internal clock to the correct
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new time zone when traveling. Alternatively, a person could wear very dark glasses, as light avoidance could help
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minimize the problems of light exposure at the wrong time of day or night.
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Resetting the body clock, Part 2: Melatonin
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Melatonin is a hormone that has been linked to the regulation of circadian rhythms and sleep cycles
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[PDF]. Melatonin is secreted by the pineal gland at night; secretion is suppressed by light exposure, and as such, the
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hormone can be thought of as a "darkness signal." If doses of melatonin are administered in the morning, circadian
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rhythms will be shifted later; evening doses shift rhythms earlier. Timing of the doses is more important than amount
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per dose, though it remains to be seen what the optimal dose and optimal time of administration is--trials have been
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done with doses from 0.5 to 10mg, at times ranging from three days before departure to five days after arrival in the
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new time zone.
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If doses of melatonin are combined with light exposure, the results are what you might expect: synergistic if both
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are administered to produce a time shift in the same direction (both earlier or both later); antagonistic otherwise.
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Sleep, wake, sleep, wake
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The second way to beat jet lag: Sleep at weird times. Slowly adjust your sleep schedule to match that of your
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destination, or keep your home sleep schedule for a while after you arrive. The problem with this is that your
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sleep-wake schedule won't match up with that of the people around you, and if you need to be awake for breakfast at 7am
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or for a meeting in the afternoon, your sleep schedule may interfere. Use this method at your own risk.
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Drugs for everything
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Lastly, we have sleep medicines. As you might guess, hypnotic medications combat insomnia and stimulants fight off
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daytime sleepiness pretty well, because by definition, that's what they do. Both benzodiazepine and non-benzodiazepine
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drugs have been shown to be effective in the first case; for the latter, the most common solution is to consume more coffee [PDF]. This works! In the study
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linked, subjects were treated with slow-release caffeine or with melatonin prior to a long eastward flight; the caffeine
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subjects were less sleepy than either melatonin or placebo. Granted, caffeine subjects also took longer to fall asleep
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later and awoke more frequently, but that may be a risk you have to take.
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Lagging behind
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Light, melatonin, drugs, strange sleep schedules. Of course, the only solution that will always work is time. The
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homeostatic and circadian processes need to realign, and while the aforementioned ways of beating jet lag can fast track
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the process, it still takes time.
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UPDATE: ; I was alerted by a friend of the existence further research of which I was
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unaware: Another way to reset your sleep-wake cycle is to stop eating . If you fast for about 12 to 16 hours, your body clock will reset, with whatever time
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you break your fast as morning. The Fuller, Lu, & Saper paper
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[PDF], published in Science , discusses the mechanism, though a more recent paper argues that the Fuller et al. results are inconclusive .
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