Jet lag, also known as time zone change syndrome or desynchronosis, occurs when people travel rapidly from east to west, or west to east in an aircraft.
Jet lag is a physiological condition that upsets our body's circadian (daily) rhythms, it is therefore classified as a circadian rhythm disorder.
Jet lag symptoms tend to be more severe when the person travels from westward compared to eastward.
Contents of this article:
Here are some key points about jet lag. More detail and supporting information is in the main article.
What are circadian rhythms?
Our circadian rhythms regulate our sleep-wake cycle.
Circadian rhythms are 24-hour cycles in the biochemical, physiological, and behavioral processes of our bodies. They are often referred to as our body clock.
Our circadian rhythms are driven by an internal time-keeping system. This biological clock is set (entrained) by external environmental factors, 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.
When our internal biological clock needs to be reset, it causes jet lag; other than long flights east or west, this type of resetting can cause problems in shift workers, and in some sleeping disorders.
What is jet lag?
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 (SCN); the SCN sits below the hypothalamus at the base of the brain.
One group is synchronized with deep sleep and the effects of physical fatigue and the other controls the dream state of rapid eye movement (REM) sleep. The group of neurons involved in REM sleep finds it harder to adjust to the new cycle and the two groups become out of sync.
The older a person is, the more severe their jet lag symptoms generally are and the longer they will take to get their body clocks back into sync. A child's symptoms will usually be much milder, and they will recover faster.
Causes of jet lag
If we travel across a number of time zones and experience daylight and darkness cycles different from the rhythms we are used to, our body clock will be out of sync (synchronization).
Our natural circadian rhythm, our sleep-wake pattern, will be upset, as will our rhythms for eating and working. Our hormone regulation may be out of sync with what is going on around us; also, our body temperature, which has a daily cycle, might be out of sync.
Until all of these factors can respond properly to our new environment, we are jet-lagged.
Traveling 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.
For instance, if you suffer from hay fever and leave the northern hemisphere in 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, for jet lag to occur, there has to be an east-west or west-east movement. Flying from Chicago to Santiago, Chile will not cause jet lag because it is directly south, no time zones are crossed. But, even a flight from the eastern coast of the United States to its western coast can 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 reduced when people are flying. This can make us slightly lethargic, resulting in a higher risk of more severe jet lag symptoms.
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 p.m. London time, it is still 4 p.m. Chicago time. Come midnight, it will be hard to sleep because your body clock it is still saying it is 6 p.m. (not bedtime).
However, if you land in Chicago from London, by 10 p.m. you will find it easier to get to sleep, because 10 p.m. in Chicago is 4 a.m. in London - 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 (or before) the flight may result in more severe jet lag.
Symptoms of jet lag
Symptoms of jet lag vary and depend on several factors, including how many time zones were traveled, the individual's age, state of health, whether or not alcohol was consumed during the flight, how much was eaten during the flight, and how much sleep there was during the flight.
The following are typical jet lag symptoms:
- Head feels heavy
- Lethargy, fatigue
- Mild depression
- Attention deficit - hard to concentrate on one thing for long
- Loss of appetite
- Slight confusion
- Dizzy unsettled feeling - this may be due to the constant movements of the aircraft
- Some gastrointestinal disturbances, such as diarrhea or constipation
Jet lag treatments and prevention
There are a number of things to do to minimize the symptoms of jet lag.
- Physical fitness and health - studies have found that people who are physically fit, rest properly, and eat a well-balanced diet tend to have fewer and lighter symptoms than other individuals.
- Control underlying medical conditions - if there is an existing medical condition, such as a lung disease, heart disease, or diabetes, following the treatment plan can help minimize the impact of jet lag.
- Dehydration - drinking plenty of liquids during the flight - preferably water and definitely not alcohol or caffeinated drinks - will help reduce symptoms.
If symptoms are usually severe - consider stopping along the way for a couple of days, or traveling by ship. Adapt to local timetables immediately; this will speed up the body clock's adaptation to a new environment.
A single light box and the OTC drug melatonin - allows travelers to avoid jet lag by resetting their circadian body clock before crossing several time zones, according to research published in The Endocrine Society's Journal of Clinical Endocrinology and Metabolism.
Sunglasses - may reduce the effects of jet lag, according to a study.
Strategic napping - The best time to nap (during or after the flight) is at nighttime in the time zone being traveled to. "Power naps" of around 20 minutes may help to reduce daytime sleepiness.
Careful caffeine use - because caffeine increases alertness, if it is consumed during the morning it may help train the body to hit the correct rhythm. However, taking caffeinated products in the late-afternoon may interfere with getting to sleep at the correct time for the new time zone.