Jet lag

According to a 1969 study by the Federal Aviation Administration, aviator Wiley Post was the first to write about the effects of flying across time zones in his 1931 co-authored book, Around the World in Eight Days.{{cite book |author-last1=Post |author-first1=Wiley |author-last2=Gatty |author-first2=Harold |date=1931 |title=Around the World in Eight Days |location=London |publisher=Hamilton}}{{cite report |url=https://www.faa.gov/data_research/research/med_humanfacs/oamtechreports/1960s/media/AM69-17.pdf#page=5 |title=Time-Zone Effects On the Long Distance Air Traveler |last1=Siegel |first1=P. V. |last2=Gerathewol |first2=Siegfried J. |date=September 1969 |publisher=Federal Aviation Administration |page=3 |last3=Mohler |first3=Stanley R. |archive-url=https://web.archive.org/web/20230413171928/https://www.faa.gov/data_research/research/med_humanfacs/oamtechreports/1960s/media/AM69-17.pdf#page=5 |archive-date=2023-04-13 |url-status=dead}} However, Post and the Federal Aviation Administration initially did not link these symptoms to circadian disruption. Instead, these effects were attributed to travel fatigue factors such as anxiety about air travel, disruption to routine, and dehydration from the dryness of the prolonged aircraft time. {{cite journal |last1=Waterhouse |first1=Jim |last2=Reilly |first2=T |last3=Edwards |first3=Ben J |title=The stress of travel |journal=Journal of Sports Sciences |date=November 2004 |volume=22 |issue=10 |pages=946-65; discussion 965-6 |doi=10.1080/02640410400000264 |pmid=15768727 |url=https://www.researchgate.net/publication/7965590}} Jet lag started associating with circadian rhythms in the 1970s with the rise of entrainment and phase shift research, mimicking similar symptoms to jet lag when rhythms were disrupted.{{cite journal |last1=Aschoff |first1=J |title=Human circadian rhythms in activity, body temperature and other functions |journal=Life Sciences and Space Research |date=1967 |volume=5 |pages=159–173 |pmid=11973844 |url=https://pubmed.ncbi.nlm.nih.gov/11973844/}} These associations began the official recognition of jet lag as an effect of circadian disruption rather than a factor of travel fatigue.

The term jet lag is inspired by how people feel after travelling rapidly over several time zones, typically on a plane or jet-like form of transportation. The body’s feeling of having to adjust to the new time zone serves as the inspiration for the “lag” component of the term.{{cite journal |last1=Arendt |first1=Josephine |title=Approaches to the Pharmacological Management of Jet Lag |journal=Drugs |date=2018 |volume=78,14 (2018) |issue=14 |pages=1419–1431 |doi=10.1007/s40265-018-0973-8 |pmid=30167980 |pmc=6182450 }} The term’s first use was found in a Los Angeles Times article on February 13, 1966. Horace Sutton wrote, “If you’re going to be a member of the Jet Set and fly off to Katmandu for coffee with King Mahedra, you can count on contracting Jet lag, a debility not unakin to a hungover. Jet Lag derives from the simple fact that jets travel so fast they leave your rhythms behind.” The term began gaining popularity soon after, continuing to increase to this day. {{cite web |url=https://books.google.com/ngrams/graph?content=jetlag&year_start=1800&year_end=2022&corpus=en&smoothing=3}}

The symptoms of jet lag can be quite varied, depending on the amount of time zone alteration, time of day, and individual differences. Sleep disturbance occurs, with poor sleep upon arrival or sleep disruptions such as trouble falling asleep (when flying east), early awakening (when flying west), and trouble remaining asleep. Cognitive effects include poorer performance on mental tasks and concentration; dizziness, nausea, insomnia, confusion, anxiety, increased fatigue, headaches, and irritability; and problems with digestion, including indigestion, changes in the frequency and consistency of bowel movements, and reduced appetite.{{cite web |last1=Doyle |first1=Ashley |title=What is a Jet Lag? |url=https://savvysleeper.org/what-is-jet-lag/ |date=10 January 2020 |website=Savvysleeper |access-date=3 June 2020 |archive-url=https://web.archive.org/web/20200925234923/https://savvysleeper.org/what-is-jet-lag/ |archive-date=25 September 2020}} The symptoms are caused by a circadian rhythm that is out of sync with the day–night cycle of the destination,{{cite journal |last1=Waterhouse |first1=Jim |last2=Reilly |first2=Thomas |last3=Atkinson |first3=Greg |last4=Edwards |first4=Ben |title=Jet lag: trends and coping strategies |journal=The Lancet |date=March 2007 |volume=369 |issue=9567 |pages=1117–1129 |doi=10.1016/S0140-6736(07)60529-7 |pmid=17398311 }} as well as the possibility of internal desynchronisation. Jet lag has been measured with simple analogue scales, but a study has shown that these are relatively blunt for assessing all the problems associated with jet lag. The Liverpool Jet Lag Questionnaire was developed to measure all the symptoms of jet lag at several times of day, and has been used to assess jet lag in athletes.{{Cite journal |last1 = Waterhouse |first1 = J. |last2 = Edwards |first2 = B. |last3 = Nevill |first3 = A. |last4 = Carvalho |first4 = S. |last5 = Atkinson |first5 = G. |last6 = Buckley |first6 = P. |last7 = Reilly |first7 = T. |last8 = Godfrey |first8 = R. |last9 = Ramsay |first9 = R. |title = Identifying some determinants of 'jet lag' and its symptoms: A study of athletes and other travellers |journal = British Journal of Sports Medicine |volume = 36 |issue = 1 |pages = 54–60 |year = 2002 |pmid = 11867494 |pmc = 1724441 |doi = 10.1136/bjsm.36.1.54 }}

Jet lag may require three hour or more hours of time zone change to occur, but some individuals can be affected by a single hour of time zone change which can include the single-hour shift to or from daylight saving time. Symptoms and consequences of jet lag can be a significant concern for athletes travelling east or west to competitions, as performance is often dependent on a combination of physical and mental characteristics that are affected by jet lag. This is often a common concern at international sporting events like the Olympics and FIFA World Cup. However many athletes arrive at least 2–4 weeks ahead of these events, to help adjust from any jet lag issues.{{Cite journal |last1=Forbes-Robertson |first1=S. |last2=Dudley |first2=E. |last3=Vadgama |first3=P. |last4=Cook |first4=C. |last5=Drawer |first5=S. |last6=Kilduff |first6=L. |year=2012 |title=Circadian Disruption and Remedial Interventions |journal=Sports Medicine |volume=42 |issue=3 |pages=185–208 |doi=10.2165/11596850-000000000-00000 |pmid=22299812 }}

Travel fatigue is general fatigue, disorientation, and headache caused by a disruption in routine, time spent in a cramped space with little chance to move around, a low-oxygen environment, and dehydration caused by dry air and limited food and drink. It does not necessarily involve the shift in circadian rhythms that cause jet lag. Travel fatigue can occur without crossing time zones, and it often disappears after one day accompanied by a night of good quality sleep.

Jet lag is a chronobiological problem,{{Cite journal |last1 = Waterhouse |first1 = J. |title = Jet-lag and shift work: (1). Circadian rhythms |journal = Journal of the Royal Society of Medicine |volume = 92 |issue = 8 |pages = 398–401 |year = 1999 |pmid = 10656004 |pmc = 1297314 |doi = 10.1177/014107689909200804 }} similar to issues often induced by shift work and circadian rhythm sleep disorders. During jet lag, there is a shift in the sleep-wake cycle, disrupting the coordinated regulation of the suprachiasmatic nucleus (SCN) of the hypothalamus. The output of the SCN influences oscillatory sleep and arousal controls, which can later lead to an effect on daily sleep-wake behavior.{{cite journal |last1=M Vosko|first1=Andrew |last2=S Colwell | first2=Christopher | last3=Y Avidan | first3=Alon|title=Jet lag syndrome: circadian organization, pathophysiology, and management strategies. |journal=Nature and Science of Sleep |date=19 August 2010 |volume=2 |pages=187–198 |doi=10.2147/NSS.S6683 |doi-access=free |pmid=23616709 |pmc=3630947 }} When travelling across a number of time zones, a person's body clock (circadian rhythm) will be out of synchronisation with the destination time, as it experiences daylight and darkness contrary to the rhythms to which it was accustomed. The body's natural pattern is disturbed, as the rhythms that dictate times for eating, sleeping, hormone regulation, body temperature variation, and other functions no longer correspond to the environment, nor to each other in some cases. To the degree that the body cannot immediately realign these rhythms, it is jet lagged.Cheng, Maria, '[https://apnews.com/article/jet-lag-travel-sleep-1393330eaa4fe4f8edc2e0e8337daae4 How to avoid the worst of jet lag and maximize your travel time]'', Associated Press, August 21, 2024

The speed at which the body adjusts to a new rhythm depends on the individual as well as the direction of travel; some people may require several days to adjust to a new time zone, while others experience little disruption.

Crossing the International Date Line does not in itself contribute to jet lag, as the guide for calculating jet lag is the number of time zones crossed, with a maximum possible time difference of plus or minus 12 hours. If the absolute time difference between two locations is greater than 12 hours, one must subtract 24 from or add 24 to that number. For example, the time zone UTC+14 will be at the same time of day as UTC−10, though the former is one day ahead of the latter.

Jet lag is linked only to the distance travelled along the east–west axis. A ten-hour flight between Europe and southern Africa does not cause jet lag, as the direction of travel is primarily north–south. A four-hour flight between Miami, Florida, and Phoenix, Arizona, in the United States may result in jet lag, as the direction of travel is primarily east–west.

Jet lag has a stronger impact when crossing more time zones over a few days. If someone has had jet lag before, then they are likely to have it again. Additional factors include arrival time, age, stress levels, sleep before travel, and use of caffeine or alcohol. Those over the age of 60 are more sensitive to circadian rhythm changes. The chances of jet lag increase with less sleep before a flight and higher stress levels.{{cite journal |last1=Herxheimer |first1=Andrew |title=Jet lag |journal=BMJ Clinical Evidence |date=29 April 2014 |volume=2014 2303|pmid=24780537|pmc=4006102 }}

Additionally, insufficient sleep before a flight can exacerbate jet lag symptoms. A well-rested state prior to travel helps the body adapt more efficiently to new time zones.{{cite journal |last1=Weingarten |first1=Jeremy A |title=Air Travel: Effects of Sleep Deprivation and Jet Lag |journal=Chest |date=2013 |volume=144 |issue=4 |pages=1394–1401 |doi=10.1378/chest.12-2963|pmid=24081353 }}

High stress levels can also disrupt the body's natural rhythms, making it more difficult to adjust to a new time zone. Stress-induced hormonal changes may interfere with sleep quality and circadian alignment.{{cite journal |last1=Arendt |first1=J |title=Physiological Changes Underlying Jet Lag |journal=British Medical Journal (Clinical Research Ed.) |date=1982 |volume=284.6310 |issue=6310 |pages= 44–46 |doi=10.1136/bmj.284.6310.144|pmid=6275937 |pmc=1495508 }}

Personal factors such as chronotype (morningness or eveningness preference), genetic predispositions, and overall health can affect how one experiences jet lag. For instance, individuals with a natural tendency to stay up late may find it easier to adjust to westward travel.{{cite journal |last1=Juda |first1=M |title=Chronotype Modulates Sleep Duration, Sleep Quality, and Social Jet Lag in Shift-Workers |journal=Journal of Biological Rhythms |date=2013 |volume=28 |issue=2 |pages=141–151 |doi=10.1177/0748730412475042|pmid=23606613 }}

Double desynchronisation is the misalignment between: The body's internal clocks and the external environment (e.g., local time at your travel destination) and the body's central and peripheral circadian clocks (i.e., misalignment within different parts of your own body).

There are two separate processes related to biological timing: circadian oscillators and homeostasis.{{cite journal |doi=10.1016/s1087-0792(98)90052-1 |title=Models of human sleep regulation |date=1998 |last1=Beersma |first1=Domien G.M. |journal=Sleep Medicine Reviews |volume=2 |issue=1 |pages=31–43 |pmid=15310511 |url=https://pure.rug.nl/ws/files/14639214/1998SleepMedRevBeersmaCorr.pdf }}{{cite journal |last1 = Dijk |first1 = D. J. |last2 = Lockley |first2 = S. W. |year = 2002 |title = Invited Review: Integration of human sleep–wake regulation and circadian rhythmicity |journal = Journal of Applied Physiology |volume = 92 |issue = 2 |pages = 852–862 |doi = 10.1152/japplphysiol.00924.2001 |pmid = 11796701 }} The master clock of the circadian system is located in the suprachiasmatic nucleus (SCN) in the hypothalamus of the brain. There are also peripheral oscillators in other tissues and organs, each having their own oscillatory rates that could be synchronized to the SCN oscillatory rate. The SCN's role is to send signals to the peripheral oscillators, which synchronise them for physiological functions. The SCN responds to light information sent from the retina and entrains its circadian rhythm to the external environment. It is hypothesised that peripheral oscillators respond to internal signals such as hormones, food intake, and "nervous stimuli" and may take longer time to synchronize to local time.{{cite book |last1 = Brown |first1 = S. A. |last2 = Azzi |first2 = A. |name-list-style = amp |year = 2013 |chapter = Peripheral circadian oscillators in mammals |title = Circadian clocks |pages = 45–66 |publisher = Springer |location = Berlin}} {{cite book |author = Center for Substance Abuse Treatment |title = Managing Depressive Symptoms in Substance Abuse Clients During Early Recovery |location = Rockville, MD |publisher = Substance Abuse and Mental Health Services Administration |year = 2008 |series = Treatment Improvement Protocol (TIP) Series, No. 48. |chapter = Appendix D: DSM-IV-TR Mood Disorders |chapter-url = https://www.ncbi.nlm.nih.gov/books/NBK64063/}}

The implication of independent internal clocks may explain some of the symptoms of jet lag. People who travel across several time zones can, within a few days, adapt their master clock SCN with light from the environment earlier. However, their skeletal muscles, liver, lungs, and other organs may adapt at different rates (peripheral circadian clocks may lag behind).{{cite journal |last1=Yamazaki |first1=Shin |last2=Numano |first2=Rika |last3=Abe |first3=Michikazu |last4=Hida |first4=Akiko |last5=Takahashi |first5=Ri-ichi |last6=Ueda |first6=Masatsugu |last7=Block |first7=Gene D. |last8=Sakaki |first8=Yoshiyuki |last9=Menaker |first9=Michael |last10=Tei |first10=Hajime |title=Resetting Central and Peripheral Circadian Oscillators in Transgenic Rats |journal=Science |date=28 April 2000 |volume=288 |issue=5466 |pages=682–685 |doi=10.1126/science.288.5466.682 |pmid=10784453 |bibcode=2000Sci...288..682Y }} This internal biological de-synchronisation is exacerbated as the body is not in sync with the environment{{snd}}a double desynchronisation, which has implications for health and mood.{{cite journal |last1=Wirz-Justice |first1=Anna |title=Biological rhythm disturbances in mood disorders |journal=International Clinical Psychopharmacology |date=February 2006 |volume=21 |issue=Supplement 1 |pages=S11–S15 |doi=10.1097/01.yic.0000195660.37267.cf |pmid=16436934 }}

Entrainment to a local time zone refers to the synchronization of an individual’s internal circadian rhythms to the external environment's 24-hour cycle, particularly in relation to light-dark cues (zeitgebers). This process is critical for overcoming jet lag, which occurs when a person's endogenous circadian timing becomes misaligned with the new local time following transmeridian travel.

Circadian rhythms in humans are generated by the suprachiasmatic nuclei (SCN) of the hypothalamus and are typically slightly longer than 24 hours, requiring daily resetting by external cues to maintain alignment with the environment.{{cite journal |last1=Arendt |first1=Josephine |title=Managing Jet Lag: Some of the Problems and Possible New Solutions. |journal=Sleep Medicine Reviews |date=2009 |volume= 13| issue = 4 |pages=249–56 |doi=10.1016/j.smrv.2008.07.011 |pmid=19147377 |url=https://doi.org/10.1016/j.smrv.2008.07.011.|url-access=subscription }} Light is the most powerful zeitgeber, and its timing, intensity, and spectral composition are key determinants of circadian phase adjustments.

The effect of light on circadian rhythms is described by the Phase Response Curve (PRC), which illustrates how light exposure at different subjective times produces phase advances or delays. A phase-advance happens when your internal clock shifts to an earlier time—you go to sleep and wake up earlier than usual. A phase-delay happens when your internal clock shifts to a later time—you go to sleep and wake up later than usual. Light exposure in the early biological morning tends to advance the circadian phase, whereas exposure in the late biological evening delays it.{{cite journal |last1=Deacon |first1=S |title=Adapting to Phase Shifts, I. An Experimental Model for Jet Lag and Shift Work. |journal=Physiology & Behavior |date=May 1996 |volume= 59| issue = 4–5 |pages=665–73 |doi=10.1016/0031-9384(95)02147-7 |pmid=8778850 |url=https://doi.org/10.1016/0031-9384(95)02147-7.|url-access=subscription }}

When individuals arrive in a new time zone, their internal biological night may still coincide with local daytime hours. Adaptation thus requires a shift in circadian phase to realign internal rhythms with the external light-dark cycle. For example, a study using bright light exposure (1,200–3,000 lux) demonstrated that strategically timed light can induce phase shifts of several hours, facilitating adaptation to new time zones.

Entrainment is also influenced by additional zeitgebers such as meal timing, scheduled activity, and chronopharmacological agents like melatonin. Melatonin, a hormone secreted during biological night, exhibits a PRC that is roughly opposite to that of light: it advances circadian rhythms when taken in the afternoon or early evening and delays them when taken in the morning. This complementarity allows for the combined use of light and melatonin to optimize re-entrainment.

However, individual variability plays a substantial role. Factors such as age, diurnal preference (chronotype), and genetic polymorphisms (e.g., in the PER gene) can affect how quickly one adapts, also in relation to the direction of travel (east-west or west-east).{{cite journal |last1=Kripke |first1=Daniel F |title=Circadian Phase Response Curves to Light in Older and Young Women and Men. |journal=Journal of Circadian Rhythms |date=July 2007 |volume= 5|page=4 |doi=10.1186/1740-3391-5-4 |doi-access=free |pmid=17623102 |pmc=1988787 }} Older adults tend to have an earlier phase angle of entrainment and may show a leftward shift in their PRC, meaning their window for phase shifting occurs earlier relative to clock time than in younger adults.

Jet lag may affect the mental health of vulnerable individuals. When travelling across time zones, there is a "phase-shift of body temperature, rapid-eye-movement sleep, melatonin production, and other circadian rhythms".{{cite journal |last1=Young |first1=D. M. |year=1995 |title=Psychiatric morbidity in travelers to Honolulu, Hawaii |journal=Comprehensive Psychiatry |volume=36 |issue=3 |pages=224–228 |doi=10.1016/0010-440x(95)90086-b |pmid=7648847}} A 2002 study found that relapse of bipolar and psychotic disorders occurred more frequently when seven or more time zones had been crossed in the past week than when three or fewer had been crossed.{{cite journal |last1=Katz |first1=G. |last2=Knobler |first2=H. Y. |last3=Laibel |first3=Z. |last4=Strauss |first4=Z. |last5=Durst |first5=R. |year=2002 |title=Time zone change and major psychiatric morbidity: the results of a 6-year study in Jerusalem |journal=Comprehensive Psychiatry |volume=43 |issue=1 |pages=37–40 |doi=10.1053/comp.2002.29849 |pmid=11788917}} Although significant circadian rhythm disruption has been documented as affecting individuals with bipolar disorder, an Australian team studied suicide statistics from 1971 to 2001 to determine whether the one-hour shifts involved in daylight saving time had an effect. They found increased incidence of male suicide after the commencement of daylight saving time but not after returning to standard time.{{cite journal |last1=Berk |first1=Michael |last2=Dodd |first2=Seetal |last3=Hallam |first3=Karen |last4=Berk |first4=Lesley |last5=Gleeson |first5=John |last6=Henry |first6=Margaret |date=January 2008 |title=Small shifts in diurnal rhythms are associated with an increase in suicide: The effect of daylight saving |journal=Sleep and Biological Rhythms |volume=6 |issue=1 |pages=22–25 |doi=10.1111/j.1479-8425.2007.00331.x}}

Constant disruption caused by chronic jet lag can cause complications to the daily metabolic cycle of an individual due to a hinted link between circadian rhythm and metabolic/epigenetic mechanisms.{{cite journal |last1=Stenvers |first1=Dirk Jan |last2=Scheer |first2=Frank A. J. L. |last3=Schrauwen |first3=Patrick |last4=la Fleur |first4=Susanne E. |last5=Kalsbeek |first5=Andries |title=Circadian clocks and insulin resistance |journal=Nature Reviews Endocrinology |date=February 2019 |volume=15 |issue=2 |pages=75–89 |doi=10.1038/s41574-018-0122-1 |pmid=30531917 |url=https://cris.maastrichtuniversity.nl/en/publications/f3ec1de0-8a94-4aac-b6f8-ec8d96e82b5b |hdl=20.500.11755/fdb8d77a-70e3-4ab7-a041-20b2303b418b |hdl-access=free }} This is due to the process of food intake acting as a Zeitgeber towards the circadian mechanisms and their control on the metabolic systems. The multiple disruptions of the circadian clock due to chronic jet lag alter eating habits causing irregular eating times, over/under eating, and metabolic inconsistencies that lead to a higher risk of type 2 diabetes and obesity.{{cite journal |last1=Sato |first1=Tomoki |last2=Sato |first2=Shogo |title=Circadian Regulation of Metabolism: Commitment to Health and Diseases |journal=Endocrinology |date=6 June 2023 |volume=164 |issue=7 |doi=10.1210/endocr/bqad086 |pmid=37253106 }}

Research on animal models have shown that cancer growth has a potential link to chronic jet lag's effect on the circadian rhythm due to constant disruption. This is due to the nature of jet lag's ability to disturb molecular structures clocks and that include cells within the body. The circadian rhythm regulates the pace of cell processes such as decay and growth, and a disturbance towards the circadian rhythm is theorized to insight tumor growth.{{Cite journal |last1=Khan |first1=Suliman |last2=Xue |first2=Mengzhou |last3=Yong |first3=V. Wee |date=2021-09-28 |title=Does chronic jet lag increase risk of cancer? |journal=Aging |volume=13 |issue=18 |pages=21810–21811 |doi=10.18632/aging.203596 |issn=1945-4589 |pmc=8507272 |pmid=34586082}} This is even of more concerned for scientist when looking at immune cells which are told to be heavily dependent on its molecular clock and now risk tumor growth and decrease functionality due to chronic jet lag.{{Cite journal |last1=Zeng |first1=Yuen |last2=Guo |first2=Zichan |last3=Wu |first3=Mengqi |last4=Chen |first4=Fulin |last5=Chen |first5=Lihua |date=2024-04-27 |title=Circadian rhythm regulates the function of immune cells and participates in the development of tumors |journal=Cell Death Discovery |language=en |volume=10 |issue=1 |page=199 |doi=10.1038/s41420-024-01960-1 |pmid=38678017 |pmc=11055927 |issn=2058-7716}}

Recent studies have demonstrated the delicate balance that circadian rhythm provides towards gut-microbiome. Chronic circadian rhythm disruption introduces a variety of disturbances within the gut that can potentially cause a multitude of issues such as inflammation. This is due to, what researchers call, a misalignment of regulatory clocks that control metabolic processes that spike insulin levels when there's an irregular timing of food intake causing inflammation.{{cite journal |last1=Crespo |first1=Manuel Tomás |last2=Trebucq |first2=Laura Lucía |last3=Senna |first3=Camila Agustina |last4=Hokama |first4=Guido |last5=Paladino |first5=Natalia |last6=Agostino |first6=Patricia Verónica |last7=Chiesa |first7=Juan José |title=Circadian disruption of feeding-fasting rhythm and its consequences for metabolic, immune, cancer, and cognitive processes |journal=Biomedical Journal |date=January 2025 |pages=100827 |doi=10.1016/j.bj.2025.100827 |pmid=39756653 |doi-access=free }} Researchers have longed believed in the correlation of proper circadian balance, the disruption of the balance and its side effects, and metabolism though more research is needed to understand underlying mechanisms.{{cite journal |last1=Woller |first1=Aurore |last2=Gonze |first2=Didier |title=Circadian Misalignment and Metabolic Disorders: A Story of Twisted Clocks |journal=Biology |date=10 March 2021 |volume=10 |issue=3 |pages=207 |doi=10.3390/biology10030207 |doi-access=free |pmc=8001388 |pmid=33801795 }}

Light is the most powerful external cue–known as Zeitgeber–for synchronizing a person’s circadian rhythm to a new time zone. Timed light exposure can significantly affect a traveler's ability to adapt to a new time zone and reduce jet lag severity. The effectiveness of light as a chronotherapeutic intervention depends on several factors including direction of travel, chronotype, and the traveler's planned activities at the final destination.

Exposure to morning light can help advance an individual’s circadian phase, making it easier for them to fall asleep earlier. This is useful for eastward travel since an individual will gain time in their final destination. Similarly, exposure to evening light can delay the phase, which is beneficial for westward travel since time will be lost at the final destination.

Strict adherence to timing is required for timed light exposure since it can be effective to help people match their circadian rhythms with the expected cycle at their destination.{{cite journal |last1=Sack |first1=R. L. |last2=Auckley |first2=D. |last3=Auger |first3=R. R. |last4=Carskadon |first4=M. A. |last5=Wright Jr |first5=K. P. |last6=Vitiello |first6=M. V. |last7=Zhdanova |first7=I. V. |year=2007 |title=Circadian Rhythm Sleep Disorders: Part I, Basic Principles, Shift Work and Jet Lag Disorders An American Academy of Sleep Medicine Review |journal=Sleep |volume=30 |issue=11 |pages=1460–83 |doi=10.1093/sleep/30.11.1460 |pmid=18041480 |pmc=2082105}} Light therapy is a popular method used by professional athletes to reduce jet lag.{{cite news |last1 = Mitchell |first1 = Peter |title = LA Dodgers bring secret weapon to Sydney |date=17 March 2014 |url=https://www.smh.com.au/sport/la-dodgers-bring-secret-weapon-to-sydney-20140317-hvjm6.html |website =The Sydney Morning Herald|access-date = 21 October 2014 }} Timed correctly, the light may contribute to an advance or delay of the circadian phase to match the destination.{{Cite web |title=The science of jet lag {{!}} Timeshifter® {{!}} Control your circadian rhythms |url=https://www.timeshifter.com/jet-lag/the-science-of-jet-lag |access-date=2025-04-24 |website=Timeshifter® |language=en-US}} To aid in timing, the US Centers for Disease Control and Prevention (CDC) recommends mobile apps which use personalized algorithms to suggest for the correct timing of light exposure and avoidance, when to use caffeine, and when to sleep.{{Cite web |title=Jet Lag {{!}} CDC Yellow Book 2024 |url=https://wwwnc.cdc.gov/travel/yellowbook/2024/air-land-sea/jet-lag |access-date=2023-01-03 |website=CDC}}

Melatonin, a hormone secreted by the pineal gland in response to darkness, serves as a biological signal of night. In contrast to light, which suppresses melatonin and delays sleep onset, exogenous melatonin can phase-shift the circadian clock by mimicking nighttime, making it an effective chronopharmacological agent for realigning circadian rhythms.{{cite journal |last1=Lewy |first1=Alfred J. |last2=Bauer |first2=Vance K. |last3=Ahmed |first3=Saeeduddin |last4=Thomas |first4=Katherine H. |last5=Cutler |first5=Neil L. |last6=Singer |first6=Clifford M. |last7=Moffit |first7=Mary T. |last8=Sack |first8=Robert L. |title=The Human Phase Response Curve (Prc) to Melatonin is About 12 Hours out of Phase with the Prc to Light |journal=Chronobiology International |date=January 1998 |volume=15 |issue=1 |pages=71–83 |doi=10.3109/07420529808998671 |pmid=9493716 }}{{cite journal |last1=Burgess |first1=Helen J. |last2=Revell |first2=Victoria L. |last3=Eastman |first3=Charmane I. |title=A three pulse phase response curve to three milligrams of melatonin in humans |journal=The Journal of Physiology |date=15 January 2008 |volume=586 |issue=2 |pages=639–647 |doi=10.1113/jphysiol.2007.143180 |pmid=18006583 |pmc=2375577 }} Melatonin receptors are situated on the SCN, which is the anatomical site of the circadian clock.{{cite journal |last1=Dubocovich |first1=Margarita L. |last2=Benloucif |first2=Susan |last3=Masana |first3=Monica I. |title=Melatonin receptors in the mammalian suprachiasmatic nucleus |journal=Behavioural Brain Research |date=December 1995 |volume=73 |issue=1–2 |pages=141–147 |doi=10.1016/0166-4328(96)00086-1 |pmid=8788492 }} The results of a few field studies of melatonin administration, monitoring circadian phase, have provided evidence for a correlation between the reduction of jet lag symptoms and the accelerated realignment of the circadian clock.{{cite journal |last1=Piérard |first1=Christophe |last2=Beaumont |first2=Maurice |last3=Enslen |first3=Marc |last4=Chauffard |first4=Françoise |last5=Tan |first5=Dux-Xian |last6=Reiter |first6=Russel J. |last7=Fontan |first7=Annick |last8=French |first8=Jonathan |last9=Coste |first9=Olivier |last10=Lagarde |first10=Didier |title=Resynchronization of hormonal rhythms after an eastbound flight in humans: effects of slow-release caffeine and melatonin |journal=European Journal of Applied Physiology |date=July 2001 |volume=85 |issue=1–2 |pages=144–150 |doi=10.1007/s004210100418 |pmid=11513308 }} When administered exogenously, via melatonin pills or melatonin gummies, it can advance or delay the circadian phase and help travelers shift faster and sleep better as they are transitioning between time zones.{{cite web |title = Melatonin for jet lag |url=https://www.timeshifter.com/jet-lag/melatonin-for-jet-lag-type-dose-timing |website =Timeshifter|access-date = 2023-01-03}}

The efficacy of melatonin depends on the dosage, timing, and individual response to it.{{Cite journal |last=Arendt |first=Josephine |date=2019-07-16 |title=Melatonin: Countering Chaotic Time Cues |journal=Frontiers in Endocrinology |language=English |volume=10 |page=391 |doi=10.3389/fendo.2019.00391 |doi-access=free |pmid=31379733 |issn=1664-2392|pmc=6646716 }} If taken early in the evening at the final destination, especially when traveling east, melatonin can help promote sleep and shift the circadian rhythm earlier. Conversely, taking it in the morning instead may delay rhythm and slow adaptation to the new eastern time zone. In addition to the concern around appropriate timing of melatonin use, the legality of the substance in certain countries is also a variable to consider. For athletes, anti-doping agencies may prohibit or limit its use, preventing them from adapting to new time zones when traveling for games and performing optimally.

In the case of short duration trips, jet lag may be minimized by maintaining a sleep-wake schedule based on the originating time zone after arriving at the destination, but this strategy is often impractical in regard to desired social activities or work obligations.{{cite journal |last1=Lowden |first1=Arne |last2=Åkerstedt |first2=Torbjörn |title=Reataining Home-Base Sleep Hours to Prevent Jet Lag in Connection with a Westward Flight Across Nine Time Zones |journal=Chronobiology International |date=January 1998 |volume=15 |issue=4 |pages=365–376 |doi=10.3109/07420529808998696 |pmid=9706413 }} Alternatively, shifting one's sleep schedule before departure by 1–2 hours to match the destination time zone may also shorten the duration of jet lag.{{cite journal |last1=Sack |first1=Robert L. |title=Jet Lag |journal=New England Journal of Medicine |date=4 February 2010 |volume=362 |issue=5 |pages=440–447 |doi=10.1056/NEJMcp0909838 |pmid=20130253 }} Especially when combined with targeted light exposure and melatonin, symptoms can be further reduced through a combination of artificial exposure to light and rescheduling, as these have been shown to augment phase-shifting.{{cite journal | url=| doi=10.1016/j.jsmc.2009.02.006 | title=How to Travel the World Without Jet Lag | year=2009 | last1=Eastman | first1=Charmane I. | last2=Burgess | first2=Helen J. | journal=Sleep Medicine Clinics | volume=4 | issue=2 | pages=241–255 | pmid=20204161 | pmc=2829880 }}

The short-term use of hypnotic medication has shown efficacy in reducing insomnia related to jet lag.{{cite journal |last1=Suhner |first1=A. |last2=Schlagenhauf |first2=P. |last3=Höfer |first3=I. |last4=Johnson |first4=R. |last5=Tschopp |first5=A. |last6=Steffen |first6=R. |title=Effectiveness and tolerability of melatonin and zolpidem for the alleviation of jet lag |journal=Aviation, Space, and Environmental Medicine |date=July 2001 |volume=72 |issue=7 |pages=638–646 |pmid=11471907 }}{{cite journal |last1=Reilly |first1=T. |title=Effect of Low-Dose Temazepam on Physiological Variables and Performance Tests Following a Westerly Flight Across Five Time Zones |journal=International Journal of Sports Medicine |date=31 December 2001 |volume=22 |issue=3 |pages=166–174 |doi=10.1055/s-2001-16379 |pmid=11354518 }} In a study, zolpidem improved sleep quality and reduced awakenings for people travelling across five to nine time zones.{{cite journal |last1=Jamieson |first1=Andrew O. |last2=Zammit |first2=Gary K. |last3=Rosenberg |first3=Richard S. |last4=Davis |first4=Jeffrey R. |last5=Walsh |first5=James K. |title=Zolpidem reduces the sleep disturbance of jet lag |journal=Sleep Medicine |date=September 2001 |volume=2 |issue=5 |pages=423–430 |doi=10.1016/s1389-9457(00)00073-3 |pmid=14592392 }} The potential adverse effects of hypnotic agents, like amnesia and confusion, have led some doctors to advise patients to test such medications prior to using them for treating jet lag.{{cite journal |last1=Dolder |first1=Christian R |last2=Nelson |first2=Michael H |title=Hypnosedative-Induced Complex Behaviours: Incidence, Mechanisms and Management |journal=CNS Drugs |date=2008 |volume=22 |issue=12 |pages=1021–1036 |doi=10.2165/0023210-200822120-00005 |pmid=18998740 }}{{Cite web |date=2016-12-07 |title=Should You Take Sleeping Pills on a Flight? |url=https://www.cntraveler.com/story/should-you-take-sleeping-pills-on-a-flight |access-date=2023-07-27 |website=Condé Nast Traveler |language=en-US}} Several cases using triazolam to promote sleep during a flight reported dramatic global amnesia.{{cite journal |last1=Morris |first1=H. H. |title=Traveler's amnesia. Transient global amnesia secondary to triazolam |journal=JAMA |date=21 August 1987 |volume=258 |issue=7 |pages=945–946 |doi=10.1001/jama.258.7.945 |pmid=3613025 }}

Cordycepin, a derivative of a natural fungal compound, has been shown to be a potential modulator of the circadian clock.{{Cite web |last1=Yirka |first1=Bob |last2=Xpress |first2=Medical |title=Protein found that keeps the circadian clock on schedule |url=https://medicalxpress.com/news/2020-05-protein-circadian-clock.html |access-date=2025-04-24 |website=medicalxpress.com |language=en}} Administration of synthetic cordycepin in mice accelerated circadian re-entrainment following an abrupt shift in the light-dark cycle. The compound was found to interact with the RUVBL2 protein, which influences gene transcription associated with circadian timing. These findings suggest a possible future application of circadian-targeting compounds as pharmacological therapeutics for jet lag and other circadian sleep-wake disorders.

{{Wikivoyage}}

• Sleep deprivation

{{Notelist}}

{{reflist}}

{{Medical resources

| ICD10 = [http://www.icd10data.com/ICD10CM/Codes/G00-G99/G40-G47/G47-/G47.25 G47.25]

| ICD9 = {{ICD9|307.45}}, {{ICD9|780.50}} {{ICD9|327.35}}

| MeshID = D021081

| DiseasesDB = 7045

}}

{{SleepSeries2}}

{{DEFAULTSORT:Jet lag}}

Category:Aviation medicine

Category:Circadian rhythm

Category:Sleep disorders

Category:Time zones