Jet lag is also known as time zone change syndrome or desynchronosis. Jet lag can occur when people travel rapidly from east to west, or west to east on a jet plane. It is a physiological condition which upsets our body's circadian rhythms - hence, it is classified as a circadian rhythm disorder. Jet lag symptoms tend to be more severe when the person travels from westward compared to eastward.
Circadian rhythm - this is the 24-hour cycle in the biochemical, physiological and behavioral process of our bodies. In layman's terms, it means our body clock. The word circadian comes from the Latin word circa meaning "about", and the Latin word diem or dies meaning "day". Our circadian rhythms are driven by an internal time-keeping system. This biological clock is entrained by external environmental occurrences, such as the light-dark cycle of night and day. Put simply, our circadian rhythm regulates our daily activities, such as sleep, waking, eating and body temperature regulation. Problems readjusting our internal biological clock causes jet lag, as do problems with shift work, and some sleeping disorders.
People with jet lag have their sleep-wake patterns disturbed. They may feel drowsy, tired, irritable, lethargic and slightly disoriented. The more time zones that are crossed rapidly, the more severe jet lag symptoms are likely to be.
Researchers from the University of Washington revealed that the disruption occurs in two separate but linked groups of neurons in a structure called the suprachiasmatic nucleus, below the hypothalamus at the base of the brain. One group is synchronized with deep sleep that results from physical fatigue and the other controls the dream state of rapid eye movement, or REM, sleep
The term "jet lag" is a relatively new one, because up to about 80 years ago nobody travelled across many time zones rapidly - there were no jets or any other kind of rapid transportation. For this reason, many languages, such as Spanish or German also use the English term "jet lag" or "jetlag" in their own languages. In French it can be called le décalage horaire.
The older a human is, the more severe are their jet lag symptoms, and the longer they will take to get their body clocks back into synch. If a 60 year-old adult travels with a child from San Francisco to London by plane, the child's symptoms will usually be much milder, and he/she will recover faster.
Causes of jet lag
If we travel across a number of time zones and experience daylight and darkness contrary to the rhythms we are used to, our body clock will be out of synch (synchronization). Our natural circadian rhythm, our sleep-wake pattern will be upset, as will our rhythms for eating and working times. Our hormone regulation may be out of synch with what is going on around us, as perhaps might be our body temperature control. Until all these factors are able to respond properly to our new environment we are jet-lagged.
Travelling through time zones, and also from the northern hemisphere to the southern hemisphere at the same time can cause additional problems. Not only does the body have to get used to a new time zone, but the seasons are different. If you suffer from hayfever and leave the northern hemisphere in autumn (fall) and land about 400 miles south of Buenos Aires, Argentina, your dormant hay fever may return. Your body will have to cope with a change in daily occurrences as well as seasonal phenomena.
However, jet lag has to have an east-west or west-east movement for jet lag to occur. Flying from Chicago to Santiago, Chile will not cause jet lag because it is only straight down, while a trip from London to Tokyo by plane will. Even a flight from the eastern coast of the USA to its western coast will cause jet lag.
Jet lag does not usually occur if the individual crossed just one or two time zones.
Experts say that there is a link between environmental levels of oxygen and susceptibility to jet lag. An airplane's cabin air pressure is much lower than it is at sea level, meaning that the amount of oxygen reaching the brain may be lower when most people are flying. This may make us slightly lethargic, resulting in a higher risk of more severe jet lag symptoms. If the flyer has an underlying medical condition, such as anemia or heart disease, having less oxygen may worsen jet lag symptoms even more. In all these cases jet lag will only occur if the flyer travels across at least two time zones (probably at least 3 time zones).
Which direction of travel is worse for jet lag?
Jet lag is normally more severe when traveling eastwards.
Which is worse, east-west or west-east? - If you travel eastward the chances of more severe symptoms are greater, because the day will seem longer.
If you land in London from Chicago at 10 pm London time, it is still 4pm Chicago time. Come midnight it will be hard to sleep, because for your body clock it is still 6pm (not bed time). However, if you land in Chicago from London, by 10pm you will find it easier to get to sleep, because 10pm in Chicago is 4am in London - for your body clock, if you live in London it is very late to be awake. A good night's sleep helps recover from jet lag more quickly.
Experts say that drinking alcohol during your flight may result in more severe jet lag symptoms when you arrive at your destination.
On the next page we look at the symptoms of jet lag and ways in which it can be treated and prevented.