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(2009-01-18 02:19:59)



分类: 自学考试信息
                    Unit Eight    Jet Lag: Prevention and Cure


  The problem of Jet Lag is one every international traveler 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 lo 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 Stale, 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 be 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.


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