Health ConditionsJet lag is a temporary physiological condition that occurs when a person's circadian rhythm is out of sync with the time zone they are in, and is a typical result of travelling rapidly across multiple time zones (east–west or west–east). Formally designated Jet Lag Disorder (JLD), it is a recognized circadian rhythm sleep disorder characterized by insomnia or excessive daytime sleepiness — and sometimes general malaise and somatic symptoms — associated with transmeridian jet travel. It is also medically known as "circadian dysrhythmia" or "desynchronosis."
Jet lag, technically referred to as circadian misalignment, results from the misalignment of the biological timing of the body with local (social) clock time, producing a range of physiological and behavioral effects. It is a consequence of circadian misalignment that occurs after crossing time zones too rapidly for the circadian system to keep pace.
Familiar to almost every intercontinental traveler is the experience of fatigue upon arrival in a new time zone, but almost as problematic are a number of other jet lag symptoms, including reduced alertness, nighttime insomnia, loss of appetite, depressed mood, poor psychomotor coordination, and reduced cognitive skills — all closely affected by both the length and direction of travel.
Jet-lagged travelers may experience disturbed sleep, daytime fatigue, poor performance in mental and physical tasks, decreased alertness, and headache. Aside from sleep and stress problems, jet lag disorder can also cause fatigue, difficulty staying alert, gastrointestinal issues, anxiety, and amnesia.
Clinical and pathophysiological studies indicate that jet lag can exacerbate existing affective disorders. It has been suggested that dysregulation of melatonin secretion and occurrence of circadian rhythm disturbances may be the common links that underlie jet lag and affective disorders.
The master network coordinating the circadian timing system is based in the suprachiasmatic nucleus (SCN) of the hypothalamus, where neurons exhibit circadian rhythms in their electrical activity and are driven by cell-autonomous molecular feedback loops. These neural activity rhythms are critical for circadian output and are reciprocally required for the sustained generation of their own internal molecular oscillations. Output from this SCN clock regulates oscillatory sleep and arousal control centers, leading downstream to the organization of daily sleep–wake behavior.
Through autonomic nervous system projections involving the superior cervical ganglia, the SCN controls the release of the major internal synchronizer melatonin. The SCN drives and controls nocturnal synthesis and secretion of the pineal hormone melatonin, which in turn interacts with melatonin receptors on SCN neurons. The SCN master clock regulates secondary oscillators present in most of the body's organs via changes in melatonin and cortisol levels and the activity of the sympathetic nervous system. Consequently, most physiological functions display rhythmic changes.
The body is synchronised to night and day by the action of sunlight through brain chemicals and neurotransmitters, especially melatonin. Many bodily processes are timed on this 24-hour physiological "clock," including temperature, hormones, digestion, heart rate, blood pressure, and brain states.
Circadian rhythms in cognitive functions, eating, sleeping, hormone regulation, body temperature, and other processes require days to re-entrain to the new time zone.
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. This is due to the process of food intake acting as a Zeitgeber ("time-giver") 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.
There are many bodily processes controlled by day-night rhythms, such as blood pressure control, feeding behaviors, and lipid and carbohydrate metabolism, among others.
There is a complex and precise bidirectional regulatory relationship between the host circadian rhythm system and the gut microbiota. The host's circadian system includes a central clock in the SCN and peripheral clocks in organs like the intestine. These clocks collectively create a rhythmic environment for the gut microbiota by regulating key physiological processes, including body temperature, hormone secretion (e.g., cortisol and melatonin), immune responses, and intestinal epithelial cell renewal.
It has been demonstrated that gut microbiota have their own diurnal oscillations in composition and function, and the microbes and their metabolites may be associated with the detrimental consequences of circadian disturbance for host metabolism. Microbiota-generated metabolites bridge host-microbiota interactions and may be essential for human physiology, and may also affect the susceptibility of the host to obesity, diabetes, and immune-mediated diseases.
Research concludes that circadian disruption — but not sleep loss or stress alone — is associated with jet-lag-related dysregulation of the innate immune system. Such immune changes might be a common mechanism for the myriad negative health effects of shift work and chronic circadian disruption. Chronic disruption of circadian timing in shift work or during chronic jet lag in animal models leads to a higher risk of several pathologies, many of which share the common risk factor of inflammation. These findings are currently from animal models and have not been fully established in human clinical studies.
The phase shift when travelling from east to west is referred to as phase-delay of the circadian cycle, whereas going west to east is phase-advance of the cycle. Roughly 75% of people find that jet lag is worse when traveling east than it is when traveling west, although jet lag differs with the direction of travel based on each individual's internal circadian clock.
The speed of resynchronization of circadian rhythms to the new time zone depends on multiple factors, including the number of zones crossed, the direction of travel, and the traveler's ability to adapt to the new location. In general, it usually takes about one day per time zone crossed for the body clock to adjust to the local schedule, meaning that crossing five time zones could require around five days for symptoms to resolve.
Factors such as age, diurnal preference (chronotype), and genetic polymorphisms (e.g., in the PER gene) can affect how quickly one adapts. Older adults tend to have an earlier phase angle of entrainment and may show a shift in their phase response curve, meaning their window for phase shifting occurs earlier relative to clock time than in younger adults. Some studies have shown that people over the age of 60 experience circadian rhythm changes more frequently.
Lack of sleep before and during travelling can also contribute to jet lag. Sleep loss during travel can worsen the symptoms of jet lag. Sleep in-flight can be maximized by minimizing alcohol consumption (which tends to reduce sleep latency but increase sleep fragmentation) and caffeine intake.
Factors exacerbating jet lag symptoms include sleep deprivation, prolonged uncomfortable sitting positions, air quality and pressure, stress, and excessive caffeine and alcohol intake.
Alcohol and caffeine can both cause dehydration, which can further exacerbate jet lag. Drinking alcohol might make a person drowsy, but it can worsen the quality of sleep.
Changes in cabin pressure and high altitudes during air travel may contribute to some symptoms of jet lag, regardless of travel across time zones. The barometric pressure on planes tends to be lower than air on the ground, similar to being at an 8,000-foot (2.44 km) altitude. While there is just as much oxygen in the air, the lower pressure may result in less oxygen reaching the bloodstream (hypoxemia), and lower oxygen levels may make a person lethargic. Low humidity levels on airplanes can also contribute to dehydration, which may make symptoms of jet lag worse if travelers do not drink enough water.
Adaptation to the destination time zone may be facilitated by shifting sleep toward the destination time zone in the days prior to the trip. Shifting sleep one hour later (for westward travel) or earlier (for eastward travel) per day in the two to three days prior to the trip may reduce the amount of time required to adjust to the destination time zone.
Melatonin is a pineal hormone that plays a central part in regulating bodily rhythms and has been used as a drug to re-align them with the outside world. The evidence base for melatonin in jet lag is among the most robust of any natural supplement in this context.
Melatonin is remarkably effective in preventing or reducing jet lag, and occasional short-term use appears to be safe. It should be recommended to adult travellers flying across five or more time zones, particularly in an easterly direction, and especially if they have experienced jet lag on previous journeys. This conclusion comes from a Cochrane systematic review of randomized controlled trials.
The results of this systematic review indicate that when travelling across a number of time zones, melatonin is an effective treatment for prevention and treatment of jet lag when used at bedtime in the day of travel and for up to four days after arrival. However, individuals differ greatly in the experience of jet lag, with some travelers extremely affected, while others report no symptoms, suggesting that individual differences may strongly influence the effectiveness of melatonin.
Not all trials have been uniformly positive. One randomized, double-blind trial compared placebo and three alternative regimens of melatonin (5.0 mg at bedtime, 0.5 mg at bedtime, and 0.5 mg on a shifting schedule) in 257 Norwegian physicians returning from a five-day trip to New York (a six-hour eastward shift), using the Columbia Jet Lag Scale as an outcome measure. The authors concluded that the use of melatonin for preventing jet lag needs further study.
The American Academy of Sleep Medicine recommends against using melatonin for general chronic insomnia in adults — the strongest evidence supports its use for circadian rhythm disruption specifically, such as jet lag and shift work.
A 2023 study found that 88% of melatonin gummies tested contained inaccurate amounts of the hormone, with actual content ranging from 74% to 347% of what the label claimed — a significant practical caveat for consumers choosing commercially available products.
The pharmacology and toxicology of melatonin need systematic study, and routine pharmaceutical quality control of melatonin products must be established. The effects of melatonin in people with epilepsy, and a possible interaction with warfarin, also need investigation.
Tryptophan is the precursor of serotonin and melatonin, which influence sleep architecture and regulate the circadian rhythm, respectively. In the pineal gland, serotonin is converted into melatonin through two additional enzymatic steps regulated by the circadian rhythm and light exposure. Serotonin itself does not cross the blood-brain barrier; the brain must synthesize it from precursors that can cross. L-tryptophan is the only dietary precursor that feeds the entire chain.
Tryptophan has been shown to decrease sleep latency, increase total sleep time, and reduce waking time and number of awakenings. Tryptophan can also regulate sleep and the circadian rhythm by increasing melatonin levels.
No clinical trials have studied L-tryptophan supplementation specifically in a jet lag population. Evidence for its sleep-promoting effects derives from general sleep research. Direct application to jet lag remains inferential, based on its role as the dietary precursor to melatonin.
Several studies have demonstrated that magnesium exerts a relaxant effect. Magnesium supplementation can reduce the concentration of serum cortisol (a stress hormone) and thus calm the central nervous system, potentially improving sleep quality. A recent study has indicated that magnesium can regulate the cellular biological clock, energy balance, and circadian rhythm, and it appears to exert a pivotal role in sleep regulation.
Magnesium has moderate evidence for general sleep improvement. Natural remedies for insomnia, such as magnesium and various B vitamins, may also support better sleep patterns. As with tryptophan, no clinical trials have examined magnesium specifically in the context of jet lag populations. Its relevance to jet lag is based on its role in sleep and circadian regulation rather than direct jet lag trial data.
Valerian root has a long history of use in European traditional herbal medicine as a mild sedative and sleep aid. It has been used in tea infusions, tinctures, and extracts for conditions including sleep disturbance and anxiety, predating modern pharmacology by centuries.
Valepotriates and valerenic acid found in valerian root are responsible for the plant's sedative and anxiolytic effects. The assisting sleep effect of valerian appears to be due to the upregulation of gamma-aminobutyric acid A (GABA) receptors; the valerenic acid contained in valerian inhibits the enzyme system responsible for the catabolism of GABA.
A systematic review published in 2000 analyzed 9 randomized clinical trials and found contradictory results and significant inconsistency in terms of patients, experimental design, and methodology. Another systematic review and meta-analysis published in 2006 analyzed 16 studies and also found significant methodological problems. A systematic review of 37 studies (29 controlled trials and 8 open-label) concluded that, although valerian is a safe herb, the evidence did not support the clinical efficacy of valerian as a sleep aid for insomnia. A meta-analysis of 18 randomized placebo-controlled trials published in 2010 concluded that valerian's effectiveness had not been demonstrated with quantitative or objective measures, although valerian could improve subjective sleep quality.
Several clinical trials have investigated the efficacy of valerian for insomnia, but the results have been mixed. A meta-analysis of 16 randomized controlled trials reported that valerian improved sleep quality compared with placebo, but the authors noted significant heterogeneity among the studies and called for further research to confirm their findings.
Available evidence suggests that valerian may be effective in improving sleep quality and reducing insomnia. No clinical trials have tested valerian specifically in a jet lag context; its application to jet lag remains based on its general sedative and sleep-supportive properties.
For over 3,000 years, the roots and berries of ashwagandha have been a staple of Ayurveda, the traditional system of medicine in India, where it is revered for its restorative properties. At its core, ashwagandha is classified as an adaptogen. Its traditional use was primarily as a general tonic (rasayana) for vitality, stress, and nervous exhaustion, not specifically for circadian disruption or jet lag.
Ashwagandha is used to modulate the hypothalamic-pituitary-adrenal (HPA) axis and neuroendocrine functions, which promote physiological homeostasis and stress resilience. Unlike conventional sedatives, which frequently mask symptoms, ashwagandha reduces the underlying stress and anxiety associated with sleep disturbances.
A systematic review and meta-analysis analyzing five randomized controlled trials with 400 participants found that ashwagandha extract exhibited a small but significant effect on overall sleep (Standardized Mean Difference –0.59; 95% Confidence Interval –0.75 to –0.42).
In an eight-week double-blind, randomized, placebo-controlled study, a significant reduction in perceived stress scores was observed with ashwagandha at both 250 mg/day and 600 mg/day. Serum cortisol levels were reduced with both doses, and participants receiving ashwagandha had significant improvement in sleep quality compared to placebo.
Preclinical research has highlighted its anti-anxiety, anti-inflammatory, and mood-stabilizing effects, but clinical evidence on its efficacy in treating sleep disturbance is limited, necessitating rigorous investigations to establish its therapeutic potential. No clinical trials have evaluated ashwagandha specifically for jet lag. Evidence for jet lag relevance is indirect, based on stress reduction and general sleep improvement.
German chamomile has been used for centuries in European herbal medicine, particularly as an infusion consumed at bedtime for promoting relaxation, reducing anxiety, and aiding sleep. It is among the most widely consumed herbal teas globally.
Although certain supplements such as valerian, hops, and kava have shown promise in clinical trials, other supplements such as German chamomile have shown limited evidence to support their efficacy as sleep aids. No clinical trials have specifically evaluated chamomile for jet lag. Its use in this context remains based on traditional application and general sedative properties.
Hops have long been used in European phytotherapy as a mild sedative, often in combination with valerian. Traditional preparations included dried strobiles in teas and tinctures.
Clinical evidence for the efficacy of hops for insomnia is limited, with most studies using hops in combination with other herbal extracts, particularly valerian. In a randomized, double-blind, placebo-controlled trial, a combination of valerian and hops modestly improved sleep quality and reduced sleep latency compared with a placebo in 184 adults with insomnia. The combination was well-tolerated, with no significant differences in adverse events between the treatment and placebo groups.
No clinical trials have evaluated hops specifically for jet lag.
In a systematic review of 13 randomized trials of persons with jet lag or shift-work disorder, caffeine improved concept formation, reasoning, memory, orientation, attention, and perception compared with placebo. Two studies specifically reviewed its effect after eastward transmeridian travel, using slow-release formulations of caffeine at a dose of 300 mg. Slow-release caffeine allowed a quicker resynchronization of hormonal rhythms, as demonstrated by mean saliva cortisol concentrations which were significantly lower than in the placebo group.
A follow-up study found that caffeine led to an objective decrease in daytime sleepiness compared with melatonin and placebo, as assessed by multiple sleep latency tests. However, both alcohol and caffeine can adversely affect quality of sleep when consumed a few hours before bedtime; caffeine intake should therefore be planned strategically to enhance daytime alertness rather than taken indiscriminately.
Other suggested natural treatments for jet lag include nicotinamide adenine dinucleotide (NADH), which may enhance mental function post-travel. Evidence for NADH in jet lag specifically is preliminary and limited; no large-scale controlled trials have confirmed this effect, and it is not currently supported by major systematic reviews on jet lag interventions.
Tyrosine, an amino acid, has shown promise in improving alertness during sleep deprivation, and has been suggested as a natural treatment to support mental function following jet lag-related sleep loss. As with NADH, evidence is preliminary and derives from sleep deprivation research rather than dedicated jet lag trials.
Manipulating diet may have a role in shifting circadian rhythms; ingesting a high-protein breakfast will promote arousal and wakefulness in the morning, and a high-carbohydrate dinner will promote sleepiness in the evening. Military personnel utilized the Argonne diet and alternating fasting and feeding periods to successfully mitigate symptoms of jet lag across nine time zones. The Argonne diet consists of four days of alternating between feasting (no calorie limit: a protein-rich breakfast and lunch, with a carbohydrate-rich supper) and fasting (under 800 kcal/day). The soldiers' interpretation of and adherence to the diet was not supervised, and jet lag symptoms were based on self-report. Evidence for this dietary approach is therefore anecdotal and observational in nature.
Food intake functions as a Zeitgeber — a time-giving environmental cue — for the body's peripheral circadian clocks. The process of food intake acts as a Zeitgeber towards circadian mechanisms and their control on the metabolic systems. In a randomized controlled trial, long-haul cabin crew implemented a self-selected meal plan primarily focused on eating three regular meals, synchronized with the light-dark cycle, on arrival — suggesting that meal timing in alignment with the destination's day-night schedule may support re-entrainment.
Staying hydrated is recommended because volume depletion can worsen the physical symptoms of jet lag. Low humidity levels on airplanes can contribute to dehydration, which may make jet lag symptoms worse if travelers do not drink enough water.
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 to fall asleep earlier — useful for eastward travel — while exposure to evening light can delay the phase, which is beneficial for westward travel.
Routinely recommended interventions based on circadian science include timely exposure to light and darkness (scheduled sleep), but the real-world effectiveness of these and other non-circadian strategies has been formally examined in a systematic review of non-pharmacological interventions for jet lag. Thirteen studies included used light exposure, physical activity, diet, chiropractic treatment, or a multifaceted intervention to counteract jet lag.
A non-pharmacological approach, including adequate exercise, hydration, and appropriate timing of exposure to bright light, can aid in the adjustment to a new time zone. The specific role of exercise timing in circadian re-entrainment has been identified as an area of interest in jet lag management research, particularly in sports medicine contexts, though the clinical evidence base remains modest compared to that for light exposure and melatonin.
Strategies to minimize the effects of jet lag include adjusting the sleep schedule according to the new location during the days preceding the trip. This approach may be helpful for travel that lasts for more than a week, but it does not appear useful for short-term trips.
When passengers are traveling, they are advised to avoid alcohol, especially while they are being treated for jet lag. Both alcohol and caffeine can cause dehydration, which can further exacerbate jet lag. Strategically timed caffeine use after arrival, however, has modest evidence for improving daytime alertness during the re-entrainment period.
5-HTP is the immediate biosynthetic precursor to serotonin, which is subsequently converted to melatonin in the pineal gland. It is referenced in the scientific literature as supporting the serotonin-melatonin pathway relevant to sleep-wake cycle regulation disrupted by jet lag. While direct RCT evidence specific to jet lag is limited, 5-HTP's role as a melatonin precursor gives it mechanistic plausibility for supporting circadian re-entrainment and sleep quality following transmeridian travel.
Caffeine is recognized by the CDC and peer-reviewed sources as a pharmacological countermeasure for jet lag-related daytime fatigue and impaired alertness. A Cochrane systematic review of 13 randomized trials found caffeine improved cognitive performance in persons with jet lag or shift-work disorder. A double-blind RCT using slow-release caffeine (300 mg) after a 7-time-zone flight demonstrated significantly reduced objective daytime sleepiness versus placebo. Caffeine functions as an adenosine-receptor antagonist, blocking sleep-promoting adenosine signaling to sustain wakefulness.
L-Tryptophan is the dietary amino acid precursor to both serotonin and melatonin, neurotransmitters central to the regulation of circadian rhythms and sleep. A US patent (No. 11850231) specifically describes compositions combining L-tryptophan with vitamins and minerals to increase melatonin synthesis as a strategy for alleviating jet lag disorder. Its mechanism is indirect: L-tryptophan crosses the blood-brain barrier, is converted to serotonin, and subsequently to melatonin, supporting circadian timing.
Melatonin has the strongest scientific evidence base for jet lag among all supplements. A Cochrane systematic review of ten randomized trials found that 8 of 10 studies showed melatonin taken close to destination bedtime decreased jet lag from flights crossing five or more time zones. It acts as a chronobiotic by binding MT1/MT2 receptors in the suprachiasmatic nucleus to shift circadian phase and promote sleep onset at the new local time. Doses of 0.5–5 mg taken at the target bedtime at the destination for 2–5 nights are most consistently supported.
Methylcobalamin (the active coenzyme form of vitamin B12) has been studied in multiple human trials for its effects on circadian rhythm phase-shifting and melatonin regulation. A crossover study found oral methylcobalamin (3 mg/day) significantly phase-advanced the 24-hour melatonin rhythm by approximately 1.1 hours versus placebo and enhanced light-sensitivity of the circadian clock. Another trial showed intravenous methylcobalamin increased daytime alertness and body temperature rhythms, suggesting a clock-modulating effect. These properties have led to its investigation and use for circadian rhythm sleep-wake disorders including jet lag type.
Vitamin B12 (primarily as methylcobalamin) has been investigated in peer-reviewed studies for its effects on circadian rhythm phase-shifting, melatonin secretion, and sleep-wake disorder treatment. Human crossover trials demonstrated that B12 phase-advances the 24-hour melatonin rhythm and enhances the circadian clock's sensitivity to light, properties relevant to resetting the clock after transmeridian travel. A clinical trial registry entry specifically lists B12 for 'Circadian Rhythm Sleep Disorder, Jet Lag Type.'
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