Jet Lag: Prevention and Cure

      The problem of Jet Lag is one every international traveller comes across at some time. But do you have to suffer? Understand what it is, and how a careful diet can minimize its worst effects, and your flights will be less stressful.

      The effects of rapid travel on the body are actually far more disturbing than we realize. Jet Lag is not a psychological consequence of having to readjust to a different time zone. It is due to changes in the body's physiological regulatory mechanisms, specifically the hormonal systems, in a different environment.

      Confused? So was John Foster Dulles, the American Secretary of State, when he flew to Egypt to conduct negotiations on the Aswan Dam. He later blamed his poor judgement on Jet Lag.

      The effects can be used to advantage, too. President Johnson once conducted an important meeting in Guam and kept the entire proceedings at Washington DC time. The White House working personnel were as fresh as paint, while the locals, in this case, were jet-lagged. Essentially, they had been instantaneously transported to America.

      Now that we understand what Jet Lag is, we can go some way to overcoming it. A great number of the body's events are scheduled to occur at a certain time of day. Naturally these have to be regulated, and there are two regulatory systems which interact.

      One timing system comes from the evidence of our senses and stomachs, and the periodicity we experience when living in a particular time zone. The other belongs in our internal clocks (the major one of which may be physically located in a part of the brain called the suprachiasmatic nucleus) which, left alone, would tie the body to a 25 hour -- yes, 25 -- rhythm. Normally the two timers are in step, and the external cues tend to regularise the internal clocks to the more convenient 24 hour period.

      If, however, you move the whole body to a time zone which is four hours different, the two clocks will be out of step, like two alarm clocks which are normally set together, but which have been reset a few hours apart. Whereas the two clocks would normally sound their alarms together, now they ring at different times. Similarly, the body can he set for evening while the sun is rising.

      In time the physiological system will reset itself, but it does take time. One easily monitored rhythm is palm sweating. A man flown to a time zone different by 10 hours will take eight days to readjust his palm sweat. Blood pressure, which is also rhythmical, takes four days to readjust.

      One reason for this discrepancy is that different bodily events are controlled by different factors. The hormone cortisol, which controls salt and water excretion, is made in the morning, wherever the body is. But the growth hormone is released during sleep, whenever in the day that sleep occurs. Normally these two hormones are separated by seven or eight hours, but if the body arrives at a destination in the early morning (local) and goes to sleep as soon as possible, the two hormones will be released simultaneously.

      What can we do about it? It is not feasible to wait four days until the body is used to the new time zone. Fortunately there is a short cut. It relies on two things -- the power of the stomach to regulate the timing of other events, and the pharmacological actions of coffee.

      The basic assumptions are:

      Coffee delays the body clock in the morning, and advances it at night. Coffee at mid-afternoon is neutral.

      Protein in meals stimulates wakefulness, while carbohydrates promote sleep.

      Putting food into an empty stomach helps synchronize the body clock.

     

      坐飞机因时差而引起的生理节奏的破坏是每个国际旅行者都会遇到的问题。但是否必须遭受其苦呢?明白了时差不适症是怎么回事，学会合理的饮食，会把这种不适症减少到最低程度，那么坐飞机旅行就不会有那么大的负担了。

      高速旅行对人身体的影响程度实际上比我们认识到的要强烈得多。时差不适症并不是人需要调整到另一时区而产生的心理症状。它的起因是人体的生理调节机制，特别是激素分泌系统，因环境的改变而发生了变化。

      迷惑了吧?美国国务卿约翰·杜勒斯飞往埃及举行阿斯旺水坝谈判时就是这样。事后他责怪自己低估了时差带来的不适症。

      时差的效果也可以加以利用。约翰逊总统曾在关岛召集了一个重要会议，所以议程都按华盛顿时间制定。白宫工作人员个个精神焕发；而关岛方面的人因时差不适个个无精打采。后者实质上等于一下子被送到了美国。

      既然了解了时差不适症，我们便可想办法来克服它。人身体的一系列生理活动每天都有一个固定的发生时间。当然，生理活动可以被调节，有两个相互影响的调节系统。

      一是计时系统，表现在我们的感觉和肠胃活动上，还有我们生活在某一时区所经历的生理周期上。另一个是在我们的人体时钟内(主要的一个体内时钟可能位于大脑的称为超交叉核的那部分中)，这些人体时钟，在不受干扰时，会使人体有一个25小时——是的，25小时——的生理节奏。通常，这两部计时系统是同步的，外界种种因素常常把内部时钟调节到更为合理的24小时一周期。

      但是如果你置身于一个与原先相差4小时的时区，两个系统就乱了节奏。这就相当于两只闹钟本来是一起定时，现在错开几小时定；本来可以一起鸣响，现在各按各的时间响。与之相似，大阳当空之时身体时钟也会被定在晚上。

      当然生理系统会及时作自我调整，但需要时间。掌心出汗是容易观察到的节律之一。一个人飞到时差为10个小时的时区里，那他就需要8个小时才能把掌心出汗调整过来。血压也是有节律的，需要四天才能调整过来。

      这种差异的原因是各种生理活动受着不同因素的制约。控制着盐和水排泄的激素性皮质醇无论身体处于何地都在早晨产生，但生长激素只在人睡眠中释放。正常情况下，这两种激素的释放时间相隔7到8小时。但如果一个人在当地时间凌晨到达某个地方，很快进入睡眠，那么两种激素就会同时释放。

      那么，我们怎么办呢?等待四个小时让身体去适应新时区不是办法。幸好，有一条捷径。它依赖于两件东西：一是肠胃调节其他生理活动节奏的能力，二是咖啡的药理作用。

      基本的道理是这样的：

      早晨咖啡减慢身体时钟，夜里加快它。下午三点左右没有作用。

      食物中的蛋白质促人清醒，而碳水化合物促人困倦。

      空腹吃东西有利于调整体内时钟。

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