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Deep inside the brain there is a clock that governs every aspect of the bodys functioning: sleep and wake cycles, levels of alertness, performance, mood, hormone levels, digestion, body temperature and so on. It regulates all of these functions on a 24-hour basis and is called the biological clock. This body clocks programmes us to be sleepy twice a day, between 3-5am and again between 3-5pm. Afternoon tea and nap are all cultural responses to our natural biological sleepiness in the afternoon. One of the major causes of the travelers malady known as jet lag is the non-alignment of apersons internal body clock with clocks in the external world. Crossing different time zones confuses thebiological clock, which then has to adjust to the new time and patterns of light and activity. To make matters more complex, not all internal body functions adjust at the same rate. So your sleep/wake may adjustto a new time zone at one rate, while your temperature adjusts at a different pace. Your digestion may beon a different schedule altogether. Though we live in a 24-hour day, the natural tendency of the body clock is to extend our day beyond 24 hours. It is contrary to our biological programming to shrink our day. That is why traveling in a westward direction is more body-clock friendly than flying east. NASA studies of long haul pilots showed that westward travel was associated with significantly better sleep quan-tity and quality than eastward flights. | 
