jet lag

Also from Answers.com... Cancer Treatments Learn about current and promising cancer treatments.

More about Jet Lag: Causes and symptoms Treatment Alternative treatment Prognosis Prevention Resources

Definition

Jet lag is a condition marked by fatigue, insomnia, and irritability that is caused by air travel through changing time zones.

Description

Living organisms are accustomed to periods of night and day alternating at set intervals. Most of the human body's regulating hormones follow this cycle, known as circadian rhythm. The word circadian comes from the Latin, circa, meaning about, and dies, meaning day. These cycles are not exactly 24 hours long, hence the "circa." Each chemical has its own cycle of highs and lows, interacting with and influencing the other cycles. Body temperature, sleepiness, thyroid function, growth hormone, metabolic processes, adrenal hormones, and the sleep hormone melatonin all cycle with daylight. There is a direct connection between the retina (where light hits the back of the eye) and the part of the brain that controls all these hormones. Artificial light has some effect, but sunlight has much more.

When people are without clocks in a compartment that is completely closed to sunlight, most of them fall into a circadian cycle of about 25 hours. Normally, all the regulating chemicals follow one another in order like threads in a weaving pattern. Every morning the sunlight resets the cycle, stimulating the leading chemicals and thus compensating for the difference between the 24-hour day and the 25-hour innate rhythm.

When traveling through a number of time zones, most people reset their rhythms within a few days, demonstrating the adaptability of the human species. Some people, however, have upset rhythms that last indefinitely.

— Paula Ford-Martin

---

also n.

A temporary disruption of bodily rhythms caused by high-speed travel across several time zones typically in a jet aircraft.

jetlagged jet'-lagged' adj.

Definition

Jet lag is a condition marked by fatigue, insomnia, and irritability that is caused by air travel through changing time zones. It is commonplace: a 2002 study of international business travelers (IBTs) found that jet lag was one of the most common health problems reported, affecting as many as 74% of IBTs.

Description

Living organisms are accustomed to periods of night and day alternating at set intervals. Most of the human body's regulating hormones follow this cycle, known as circadian rhythm. The word circadian comes from the Latin, circa, meaning about, and dies, meaning day. These cycles are not exactly 24 hours long, hence the "circa." Each chemical has its own cycle of highs and lows, interacting with and influencing the other cycles. Body temperature, sleepiness, thyroid function, growth hormone, metabolic processes, adrenal hormones, and the sleep hormone melatonin all cycle with daylight. There is a direct connection between the retina (the light-sensitive structure at the back of the eye) and the part of the brain that controls all these hormones. Artificial light has some effect but sunlight has much more. Disruption of circadian rhythms affects the sleep-wake cycles of night-shift workers as well as travelers.

When people are without clocks in a compartment that is completely closed to sunlight, most of them fall into a circadian cycle of about 25 hours. Normally, all the regulating chemicals follow one another in order like threads in a weaving pattern. Every morning the sunlight resets the cycle, stimulating the leading chemicals and thus compensating for the difference between the 24-hour day and the 25-hour innate rhythm.

When traveling through a number of time zones, most people reset their rhythms within a few days, demonstrating the adaptability of the human species. Some people, however, have upset circadian rhythms that last indefinitely.

Causes & Symptoms

Traveling through a few time zones at a time is not as disruptive to circadian rhythms as traveling around the world can be. The foremost symptom of jet lag is altered sleep pattern—sleepiness during the day, and insomnia during the night. Jet lag may also include indigestion and trouble concentrating. Individuals afflicted by jet lag will alternate in and out of a normal day-night cycle.

Treatment

Exposure to bright morning sunlight cures jet lag after a few days in most people. A few will have prolonged sleep phase difficulties. For these, there is a curious treatment that has achieved success. By forcing one's self into a 27 hour day, complete with the appropriate stimulation from bright light, all the errant chemical cycles will be able to catch up during one week.

When selecting an international flight, individuals should try to arrange an early evening arrival in their destination city. When an individual is traveling to a destination in the east, he or she can try going to bed and waking up a few hours earlier several days before their flight. If travel is to the west, going to bed and waking up later than usual can help the body start to adjust to the upcoming time change. More specific recommendations are available as of 2002, tailored to whether the person is traveling through six time zones, 7–9 zones, or 10 or more.

The following precautions taken during an international flight can help to limit or prevent jet lag:

• Stay hydrated. Drink plenty of water and juices to prevent dehydration. Beverages and foods with caffeine should be avoided because of their stimulant properties. Alcohol should also be avoided.
• Stretch and walk. As much movement as possible during a flight helps circulation, which moves nutrients and waste through the body and aids in elimination.
• Stay on time. Set watches and clocks ahead to the time in the destination city to start adjusting to the change.
• Sleep smart. Draw the shade and sleep during the evening hours in the destination city, even if it is still daylight outside of the airplane. Earplugs and sleep masks may be helpful in blocking noise and light. Many airlines provide these items on international flights.
• Dress comfortably. Wear or bring comfortable clothes and slippers that will make sleeping during the flight easier.

Once arriving in their destination city, individuals should spend as much time outdoors in the sunlight as possible during the day to reset their internal clock and lessen the symptoms of jet lag. Bedtime should be postponed until at least 10 P.M., with no daytime naps. If a daytime nap is absolutely necessary, it should be limited to no more than two hours.

To promote a restful sleeping environment in a hotel setting, travelers should request that the hotel desk hold all phone calls. Because sleeping in too late can also prolong jet lag, an early wake up call should be requested if an alarm clock is not available. If the hotel room is noisy, a portable white noise machine can help to block outside traffic and hallway noises. A room air conditioner or fan can serve the same purpose. The temperature in the room should also be adjusted for sleeping comfort.

New information shows that exercise when at the destination can also help. When headed westbound, travelers should exercise for one hour in the evening. If going eastbound, they do best by exercising in the morning.

All antioxidants help to decrease the effects of jet lag. Extra doses of vitamins A, C, and E, as well as zinc and selenium, two days before and two days after a flight help to alleviate jet lag. Melatonin, a hormone that helps to regulate circadian rhythms, can also help to combat jet lag. Melatonin is available as an over-thecounter supplement in most health food stores and pharmacies. Reports in 2002 show that the drug is safe for short-term use and recommend 5 mg between 10 pm and midnight at the destination to help fall asleep and to sleep better.

If weather prevents an individual from spending time in the sunlight, light therapy may be beneficial in decreasing jet lag symptoms. Light therapy, or phototherapy, uses a device called a light box, which contains a set of fluorescent or incandescent lights in front of a reflector. Typically, the patient sits for 30 minutes next to a 10,000-lux box (which is about 50 times as bright as an ordinary indoor light). Light therapy is safe for most people, but those with eye diseases should consult a healthcare professional before undergoing the treatment.

In 2002, a team from Flanders University invented new jet lag sunglasses equipped with a vision device that used light to stimulate travelers' brains. They believed that wearing the glasses before and during flights could help the internal human clock adjust more easily to changing time zones. The researchers were looking for a commercial partner to help them further study the glasses and make them widely available. The effectiveness of glasses or other head-mounted light devices is still uncertain, however. A team of researchers at Columbia University reported in the fall of 2002 that the use of a head-mounted light visor yielded only modest improvement in the test subjects' symptoms of jet lag.

Allopathic Treatment

In cases of short-term insomnia triggered by jet lag, a physician may recommend sleeping pills or prescription medication. Such medication should be taken only under the guidance of a health care professional.

A newer medication that is considered investigational is a melatonin agonist presently known as LY 156735. An agonist is a drug that stimulates activity at cell receptors that are normally stimulated by such naturally occurring substances as melatonin. LY 156735 was found to speed up the readaptation time of volunteer subjects following a simulated 9-hour time shift.

Another new area of research involves the genes that encode the proteins governing circadian rhythms. It is known as of late 2002 that differences among individuals in adaptability to time zone changes are to some extent genetically determined. Targeting the genes that affect this adaptability may yield new treatments for jet lag and other disorders of circadian rhythm.

Expected Results

Jet lag usually lasts 24–48 hours after travel has taken place. In that short time period, the body adjusts to the time change, and with enough rest and daytime exposure to sunlight, it returns to normal circadian rhythm.

Prevention

Eating a high-protein diet that is low in calories before intended travel may help reduce the effects of jet lag.

Resources

Books

Czeisler, Charles A., and Gary S. Richardson. "Disorders of Sleep and Circadian Rhythms." In Harrison's Principles of Internal Medicine, edited by Anthony S. Fauci, et al. New York: McGraw-Hill, 1998.

Periodicals

Boulos, Z., M. M. Macchi, M. P. Sturchler, et al. " Light Visor Treatment for Jet Lag After Westward Travel Across Six Time Zones." Aviation, Space, and Environmental Medicine 73 (October 2002): 953–963.

Garfinkel D. and N. Zisapel. "The Use of Melatonin for Sleep." Nutrition 14 (January 1998): 53–55.

"Jet Lag Sunglasses Help Body Clock Tick." Optician (August 2, 2002): 1.

Monson, Nancy. "What Really Works for Jet Lag." Shape (August 2002): 78.

Nickelsen, T., A. Samel, M. Vejvoda, et al. "Chronobiotic Effects of the Melatonin Agonist LY 156735 Following a Simulated 9h Time Shift: Results of a Placebo-Controlled Trial. " Chronobiology International 19 (September 2002): 915–936.

Parry, B. L. " Jet Lag: Minimizing Its Effects with Critically Timed Bright Light and Melatonin Administration." Journal of Molecular Microbiology and Biotechnology 4 (September 2002): 463–466.

Rogers, H. L., and S. M. Reilly. " A Survey of the Health Experiences of International Business Travelers. Part One—Physiological Aspects." Journal of the American Association of Occupational Health Nurses 50 (October 2002): 449–459.

Wisor, J. P. "Disorders of the Circadian Clock: Etiology and Possible Therapeutic Targets." Current Drug Targets: Cns and Neurological Disorders 1 (December 2002): 555–566.

Organizations

American Sleep Disorders Association. 1610 14th Street NW, Suite 300. Rochester, MN 55901. (507) 287-6006.

National Sleep Foundation. 1367 Connecticut Avenue NW, Suite 200. Washington, DC 20036. (202) 785-2300.

[Article by: Paula Ford-Martin; Rebecca J. Frey, PhD]

Extreme tiredness and other physical effects felt by a person after a long flight across different time zones.

jet-lagged adj.

See the Introduction, Abbreviations and Pronunciation for further details.

For more information on jet lag, visit Britannica.com.

Disorientation, fatigue, and disrupted sleep patterns associated with long-distance jet aeroplane flights. Jet lag can impair the performance of athletes competing abroad. Apparently, it desynchonizes major circadian rhythms, which require time to readjust before an athlete's condition returns to normal. On the basis of empirical studies on runners crossing the Atlantic, athletes are generally advised to allow 1 day to readjust for each time zone shift.

A temporary disruption of the body's biological clock experienced by persons who travel across several time zones by airplane. The effects of jet lag, which may include fatigue and irritability, generally disappear after a few days as the body's internal rhythms readjust themselves to the new time frame.

Jet lag refers to a group of symptoms that affect travellers following rapid transition across multiple time zones. The syndrome includes feelings of fatigue and inertia, difficulties in concentrating and in sleeping, gastrointestinal problems, and a general malaise. It is distinct from travel fatigue which is associated with tiredness after the hassles of a long journey, and which occurs after flying north or south. Jet lag is therefore a relatively modern phenomenon, associated exclusively with long-haul flights.

The cause of jet lag is disturbance of the normal circadian rhythms, referring to biological cycles that recur over the solar day. These rhythms are controlled by the body 'clock' located in the suprachiasmatic nucleus cells of the hypothalamus. Nerve connections with the pineal gland (which secretes melatonin) and the retina allow the body clock to react to light in the external environment. Consequently, the body responds rhythmically to the alternations of light and darkness. The hormone melatonin is secreted as darkness falls, causing peripheral vasodilation, a drop in body temperature, and promoting sleep. Melatonin is inhibited by light and so alertness and wakefulness are associated with daytime light. The alternation of light and darkness in the environment locks the timing of the internal body clock into a 24-hour cycle.

The synchronization of the human circadian rhythm with external local time is disrupted after travelling across different time zones. It takes some days for the body clock to adjust to the new environment, depending on the direction of flight and the number of time zones crossed. Jet lag is more severe and lasts longer, the greater the number of time zone transitions. It takes longer to adjust going eastwards compared with westward travel, the body clock coping more easily with a phase delay. Physical fitness helps combat the effects of jet lag, whilst ageing individuals compensate for any reduced capability to cope by using their previous experience. Generally it takes on average one day for each time zone traversed for symptoms to disappear totally.

Various means have been promoted to help cope with jet lag. These include pharmacological, dietary, and behavioural methods. Effective treatments are based on influencing the body clock directly or manipulating the sleeping or wakefulness phases of the day. Behavioural methods attempt to accelerate the phase advance or phase delay of the body clock, according to requirements of the trip.

The influence of a drug on jet lag symptoms depends on its mode of action. A chronobiotic refers to a direct effect on the body clock whereas a hypnotic initiates the drug's sleep-promoting characteristics. This explains why sleeping pills have been used as antidotes to jet lag. In particular the benzodiazepines have been adopted for use. Temazepam has been the minor tranquillizer of choice, although it may have hangover effects in some individuals. Shorter-acting hypnotics such as zolpidem are preferable for individuals severely affected.

Synthetic versions of melatonin may benefit travellers, but there are cautions. Timing of administration is crucial and should fit the phase–response curve of the drug. Administration of the drug in the hours before the trough of the body temperature rhythm is likely to advance the body clock, whilst administration of melatonin in the hours after this nadir should delay it. Melatonin is available only by prescription in most European countries, although it can be accessed in any drugstore in the USA. The British Olympic Association has not recommended use of melatonin or sleeping pills as a means of coping with jet lag.

Light visors have been suggested for promoting adjustment to the new time zone. Light inhibits melatonin secretion and constitutes a major environmental signal for the brain's timekeeping function. Bright light is necessary to fulfil this role and its phase–response curve is the opposite of melatonin's. Travellers should seek natural daylight early in the morning after travelling westwards, but would benefit from a lie-in for two days or so after travelling east.

The macronutrients in diet have been proposed for promoting alertness and drowsiness as required while the body's rhythms are desynchronized. The theory is that carbohydrates contain tryptophan, a precursor of serotonin, and so would increase drowsiness. By contrast, a protein diet would increase tyrosine levels, a substrate for noradrenaline (norepinephrine), thereby promoting alertness during the day. As yet there is no convincing evidence that dietary manipulation relieves jet lag: the timing rather than the type of meals seems to be the key.

Caffeine can help maintain wakefulness during the day but should be avoided before retiring to bed owing to its effect in stimulating the central nervous system. Alcohol too is a poor nightcap as its promotion of diuresis is likely to disrupt sleep. It is important to drink more than the normal daily intake, since the body may be dehydrated after the long time in the aircraft's dry air.

Indeed attention to fluids should start during flight. Fruit juices are preferable to tea, coffee, and alcohol which have diuretic effects. Light exercise — such as isometric contractions while seated, or gentle stretching at the back of the plane — will help to avoid joint stiffness and risk of deep vein thrombosis. The latter refers to blood clotting due to staying in a restricted seated posture for too long. Use of elasticated stockings to avoid blood pooling in the lower limbs has also been advocated.

Behavioural approaches to dealing with jet lag cover activity prior to embarkation, on the plane, and for days after arrival. Being well prepared for the journey and keeping refreshed during it do seem to be beneficial. Adjusting the normal sleep–wakefulness cycle for days prior to departure is too disruptive but an adjustment of bedtime by 1–2 hours can help prior to taking an eastward-bound flight. Strategies for the first few days after arrival will depend on the direction of the flight. After the first day, it should be possible to fit in closely with habitual activity of local residents. Effects of jet lag are transient, periodic, and should not entail avoidance of activity. Nevertheless, business people should allow time to adjust and should not schedule important meetings for the evening (or morning after travelling eastwards) until they have had the time to overcome the worst symptoms. Napping in the afternoons during the period of resynchronization is not advised since it may anchor circadian rhythms in the time zone of departure. For brief visits (a few hours) it is possible to maintain the body clock in its unadjusted state but the strategy required is outside the reach of the vast majority of travellers. For those a positive mindset helps to shrug off transient symptoms when they are at their most severe. Experience of previous personal strategies for coping with travel stress can reduce symptoms to subliminal levels. Travellers can therefore learn some tips on what works best for them when exposed to jet lag.

(Published 2004)

— Thomas P. Reilly

Bibliography
• Waterhouse, J. M., Minors, D. S., Waterhouse, M. E., Reilly, T., and Atkinson, G. (2002). Keeping in Time with your Body Clock.

---

IN BRIEF: Suffering from disruption of normal (sleep) patterns due to travel through several time zones.

This entry is from Wikipedia, the leading user-contributed encyclopedia. It may not have been reviewed by professional editors (see full disclaimer)