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Embarking on journeys that span oceans and continents for short periods has been a significant part of my life over the past 15 years. Along the way, I've encountered the all-too-familiar challenge of jet lag, an uninvited companion on my travels, that is, until I delved into understanding the intricacies of how the environment can influence our brain's sleep and wake cycles.
Jet lag is a well-researched and commonly experienced temporary health disturbance experienced by most individuals after rapid trans-meridian travel (3 or more timezones). Jetlag affects people differently depending on individual factors such as habits, health status, body mass index, activity level, stress, and regular sleep quality/habits. It typically manifests through several symptoms, including fatigue or sleepiness during the day, a noticeable decline in mental and physical faculties, difficulty sleeping, and digestive issues. The severity and persistence of these symptoms intensify as one travels across more time zones; for instance, traversing 3 to 4 time zones may lead to less pronounced symptoms than making a journey across 10 to 12 time zones (PMID 20130253). Additionally, the direction in which one travels significantly impacts the jet lag experience (PMID 20204161).
Through medical research and trial and error, I've discovered methods that have significantly alleviated this travel-induced burden. It's important to note that what I share comes from personal experience and accumulated knowledge, not medical advice. I encourage anyone looking to alter their sleep patterns or manage jet lag to consult a healthcare professional before implementing any strategies. I aim to share these insights in the hope that they offer some relief to fellow travelers navigating the time shifts of our global journeys.
Jet lag isn't a challenge exclusive to earthbound travelers; it's also a critical concern for travel beyond our atmosphere. Since the dawn of space exploration in the 1960s, NASA has invested millions into research to mitigate jet lag and optimize sleep cycles. Astronauts embarking on missions outside our atmosphere face the same challenges as professional travelers, with the added need to adhere to meticulously planned and scheduled missions, including sleep/wake schedules dictated by the unique demands of space travel and the absence of natural light cycles. This stringent synchronization is vital not only for the astronauts' health and well-being but also for the success of their missions, where every thought, moment, and task is critical. Through this extensive research, space exploration has contributed significantly to our understanding of sleep science, offering insights that benefit astronauts and all of us seeking ways to combat jet lag.
It is pivotal to understand that the foundation of our sleep/wake cycles, along with many other rhythmic patterns in our lives and the natural world, is deeply rooted in the cyclical transition between night and day. This “diurnal cycle,” a result of the Earth's rotation on its axis, has consistently shaped the behavior and physiology of countless species, including humans since life on Earth existed. The alternating periods of light and darkness serve as powerful cues for our biological clocks, influencing everything from hunger and sleep patterns to hormonal secretions. This natural timekeeper dictates our physical, mental, and behavioral changes over 24 hours, aligning our internal processes with the external environment. It's a testament to how closely intertwined life on Earth is with the celestial dance of our planet, underscoring the night and day cycle as a fundamental pillar of existence.
The average human sleep/wake cycle, known as the circadian rhythm, typically follows a 24-hour cycle that aligns with the Earth's day-night cycle. For most adults, a regular cycle involves approximately 7 to 9 hours of sleep per night, with sleep onset occurring between 9 PM and 11 PM and wake-up times between 6 AM and 8 AM. This cycle is influenced by external cues like light and darkness and internal biological clocks that regulate the release of hormones such as melatonin, which promotes sleep, and cortisol, which helps wake us up.
Our body's drive for sleep builds up throughout the day, peaking at night, facilitating sleep onset. During the night, our body cycles through different sleep stages, including rapid eye movement (REM) and non-REM sleep, each playing critical roles in various vital processes, such as memory consolidation and muscle repair. Upon exposure to morning light, our body reduces melatonin production, increasing wakefulness and alertness, thus resetting the cycle.
Travel, especially when it spans more than 3 hours of the time difference, can significantly disrupt our natural sleep/wake cycles. This disruption occurs because rapid travel forces our bodies to adjust to a new day-night cycle that's out of sync with our internal circadian rhythms, which are still aligned with the time zone of our departure point. The internal clock in our brain, which relies on signals like daylight to help regulate sleep, wakefulness, and other physiological functions, suddenly mismatched with the local environment. This mismatch can lead to various symptoms of jet lag, including sleep disturbances, fatigue, difficulty concentrating, and mood changes. This constellation of symptoms is what we call “jetlag.” Essentially, our biological clocks need time to reset to the local time, which can take several days, depending on the individual and the extent of the time change.
Tackling jet lag involves resetting our internal clock or aligning our circadian, hormonal, digestive, and other bodily rhythms—with the new time zone we find ourselves in. So, how do we manage this?
The concept of entrainment, as discovered by Dutch scientists in the 16th century, originally described the phenomenon of synchronization among physical systems. This early observation noted how separate pendulum clocks mounted on the same wall would, over time, swing at the same rate, even if they started at different rhythms. This intriguing discovery shed light on how dynamic systems align their cycles through interaction when nearby. This principle of entrainment, while first observed in mechanical objects, has since been applied to understand similar patterns of synchronization in biological systems, including human behavior and physiological processes. It underscores a fundamental aspect of nature: the intrinsic tendency of systems to harmonize with their surroundings, leading to a coherent, unified state.
At its core, entrainment involves synchronizing two or more systems' rhythms, where one system with a more robust, more consistent, or dominant rhythm acts as a pacemaker, guiding the rhythm of the other system(s) toward synchrony. This concept is evident in both mechanical and biological contexts. For entrainment to occur, there needs to be a pacemaker—a "stronger clock"—that provides a steady, influential signal strong enough to override the inherent rhythms of other systems and align them with its own.
In mechanical systems, like the example of pendulum clocks mounted on the same wall, the clock with the most consistent and robust swinging motion can influence the timing of swings in neighboring clocks, leading them to sync up eventually. Similarly, in biological systems, entrainment involves external environmental cues, such as the light-dark cycle, acting as a pacemaker to synchronize an organism's internal biological clock. The strength and consistency of the external cue are crucial for effective entrainment; the signal must be clear and robust enough to reset the internal rhythm according to the external cycle, like the regular rise and fall of natural light levels is a potent trainer of human circadian rhythms, helping to adjust our internal clocks to local time after traveling across time zones. The interaction between the robust external pacemaker and the flexible internal rhythms facilitates the alignment necessary for synchronization, ensuring the organism operates in harmony with its environment.
Entrainment relies on the ability of one rhythm to influence and align with another, but synchronization fails when there's too great a disparity between the two clocks. Suppose the difference in rhythms is too significant. In that case, the weaker or slower rhythm cannot adjust quickly enough to match the pace of the dominant one, or the signals from the dominant rhythm need to be more robust and consistent sufficient to effect change. This misalignment means that, rather than syncing, the two systems may continue to operate independently or need help finding a stable, familiar rhythm. This principle applies across both mechanical and biological systems, illustrating that for entrainment to be successful, the rhythms must be sufficiently compatible to allow for a gradual and achievable adjustment.
Modifying our sleep/wake cycles requires a deliberate and sometimes forceful, yet gradual, adjustment of our habits and exposure to environmental cues. This modification requires consciously manipulating the factors that influence our internal circadian rhythms.
Though the SCN endogenously generates circadian oscillations, they need to be entrained to the 24-hour day by external cues. Light exposure is endogenous circadian rhythms' most crucial synchronizing agent (PMID 9383985). One of the most effective ways to entrain a new sleep cycle is by controlling our exposure to light, as light is a primary cue that signals our brain to either wake up or wind down. Light plays a crucial role in regulating our circadian rhythms through photic entrainment and is controlled primarily through melanopsin-containing cells located in the retina, which are sensitive to blue light and are directly connected to the suprachiasmatic nucleus (SCN) in the brain, which is considered the body's master clock. The SCN coordinates the body's circadian rhythms, including the sleep/wake cycle.
The suprachiasmatic nucleus (SCN) plays a crucial role in regulating circadian rhythms and influences the hypothalamus in several key ways to maintain these daily cycles. The SCN is a part of the hypothalamus, positioning it ideally to exert direct influence over various hypothalamic functions.
The SCN is essentially the body's master clock. It receives direct input from the retina concerning light and darkness, which it uses to synchronize the body’s internal clock to the 24-hour day-night cycle. The SCN regulates and resets circadian rhythms by processing this light information, coordinating daily activity cycles, sleep, hormone release, body temperature, and other physiological processes.
The SCN influences other parts of the hypothalamus that control hormone secretion, particularly those involving the pituitary gland. For example, it regulates the timing of cortisol release by the adrenal glands via the hypothalamic-pituitary-adrenal (HPA) axis and the release of melatonin from the pineal gland, which is crucial for sleep-wake patterns. The SCN controls these releases through several signaling pathways involving various neurotransmitters and neuropeptides.
The SCN also communicates with the regions of the hypothalamus that regulate the autonomic nervous system, which controls bodily functions that are not consciously directed, such as heart rate, digestion, and respiratory rates. By regulating these functions in a circadian manner, the SCN helps ensure that the body’s internal states are optimized for different times of the day.
The SCN’s influence on the hypothalamus affects hormonal, behavioral, and physiological responses. For instance, it helps regulate feeding behavior by impacting the hypothalamic centers that control appetite and satiety.
There are three types of chromophores in the eye; two of which are considered photoreceptors, and one of which is considered a photoacceptor. Many people have heard of rods and cones, the retina's photoreceptors. These specialized cells convert photons to electricity so we can see the world. But, there is a third type of cell in the eye, a photo-acceptor that receives protons and influences biological processes. These cells are called independently photosensitive retinal ganglion cells or iPRGC cells. The unique aspect of ipRGCs is their sensitivity to a specific wavelength of light—blue light in the range of 400-500 nm (or 6,000K-7,000K)—which is abundant in morning light but also emitted by many electronic devices. When light enters the eye and strikes these ipRGCs, they send signals to the SCN, informing it about the external light conditions. This information allows the SCN to adjust the body's internal clock accordingly. For instance, exposure to natural light in the morning helps signal the body to wake up and increase alertness. Conversely, as light decreases at sunset, it signals the body to produce melatonin, a hormone created in the pineal gland that promotes sleep, peaking during the night and returning to baseline trough levels during the day.
This sensitivity means that exposure to blue light from screens late at night can mislead the SCN into thinking it's still daytime. This disrupts the natural sleep/wake cycle by inhibiting the production of melatonin, making it harder to fall asleep. Understanding the role of ipRGCs and light exposure in regulating circadian rhythms highlights the importance of managing our light environment for better sleep health and overall well-being.
Historically viewed as primarily responsible for motor control and balance, the cerebellum's role extends far beyond these functions. It acts as a central orchestrator within the brain, influencing many bodily functions, including sleep regulation. This expanded understanding of the cerebellum aligns with its extensive connections to the cerebrum. Through brainstem pathways, it receives signals from muscle and joint receptors, the vestibular system, and the cerebral cortex. It then sends excitatory signals to the cerebrum through the thalami and neocortex, forming a complex, reciprocal relationship.
Research into the cerebellum's involvement in sleep began in the 1970s and has since deepened. Recent studies have explored how the cerebellum interacts with the cerebral cortex during sleep. Evidence suggests that during slow oscillations typical of sleep, the neocortex may help regulate cerebellar activity, and in turn, the cerebellum might fine-tune the neocortex's synchrony (PMID 28431742). This dynamic interaction suggests that both regions collaboratively manage sleep and wakefulness cycles. For instance, when the cerebral cortex slows down during sleep, it similarly reduces cerebellar activity, leading to sleep. Conversely, stimulating the cerebellum or cortex through physical activity can delay sleep onset and influence wakefulness cycles. This intricate relationship underscores the cerebellum's significant, yet underappreciated, role in broader brain function and sleep regulation.
Adjusting your sleep/wake cycle to a new rhythm often necessitates a strategic approach, leveraging tools that directly influence the body's internal clock. To do this, you will need four tools— a sleep mask, melatonin, an alarm clock, and a bright light—each plays a unique role in this process:
A sleep mask is a simple yet effective tool for blocking out light, crucial for initiating and maintaining sleep. Creating a dark environment helps signal to your brain that it's time to rest, fostering deeper sleep, especially during times or in places where controlling external light isn't possible.
Melatonin is a supplement that mimics the body's natural production of the sleep hormone. As such, it can be pivotal in adjusting sleep patterns. Taking melatonin before your desired bedtime can help cue your body to prepare for sleep, aligning your internal clock with your new schedule more swiftly. It's beneficial for counteracting jet lag's effects or shifting sleep schedules forward or backward.
An alarm clock is essential for ensuring consistency in wake-up times, a critical factor in resetting your sleep cycle. By setting an alarm for the same time each morning, you help your body get accustomed to a new wake-up schedule, reinforcing your desired sleep/wake cycle through regularity.
Exposure to bright light, particularly in the morning, signals to your brain that it's time to wake up and reduces melatonin production. This exposure helps reset your internal clock by aligning your wakefulness with external daylight cues, effectively shifting your circadian rhythm to the desired schedule. For those unable to get natural sunlight exposure, specially designed bright light devices can serve as an adequate substitute, mimicking the effects of natural light on the body.
Caffeine is the most widely used psychoactive drug found in over 70 different products, with well-studied biological effects similar to cocaine and amphetamines (24761274). These effects and their pharmacokinetics are both critical to our jet lag hack. Research has demonstrated that consuming caffeine can alter your circadian rhythm. To utilize caffeine properly, it is vital to understand how caffeine affects arousal and alertness. Caffeine is a central nervous system stimulant well-known for its ability to increase arousal and alertness. Its effects are primarily due to its interaction with adenosine, a neurotransmitter that promotes sleep and relaxation.
Adenosine naturally accumulates in the brain during wakeful periods and binds to adenosine receptors, leading to neural activity that makes us increasingly tired. It's part of the homeostatic drive for sleep, meaning the longer we're awake, the more adenosine builds up and the sleepier we become.
Caffeine mimics adenosine's shape and size, competently binding to receptors without activating them. Think of it like sticking any random key into a lock. By blocking these receptors, caffeine prevents adenosine from binding and increases neuronal firing in the brain. This blockade has several downstream effects, such as releasing neurotransmitters like dopamine and norepinephrine, which can promote arousal and alertness, increase focus, and reduce the perception of fatigue.
Moreover, because the blocked adenosine can no longer promote sleepiness, individuals typically feel more awake and alert after consuming caffeine. However, once the caffeine is metabolized and its effects wear off, the accumulated adenosine can bind to its receptors again, often leading to a "crash" or a sudden tiredness.
Those are the “ingredients” of the “recipe”; now we have to discuss how to implement them.
NASA's circadian rhythms and jet lag research have provided valuable insights into how the human body adapts to time zone changes. According to their findings, as a rule of thumb, the duration of natural alignment is 0.5 days per time zone crossed in a westerly direction, i.e., 2 h per day, and one day per time zone crossed in an easterly direction, i.e., 1 h per day (PMID 20204161) This means for more substantial time zone shifts, such as those experienced during international travel across several time zones, the body may need several days to adapt to the local time fully. For instance, traveling across eight time zones might require approximately eight days for one's internal clock to fully adjust to the new local time.
With the strategies we will discuss, I have pushed that limit with very few issues. I can comfortably adjust (entrain) at 2 hours daily, but not more than 2.5.
The first step in preparing for your journey involves a bit of simple arithmetic to establish how many days you'll need to adjust to the new time zone. You start by calculating the time difference between your time at the current location (Tc) and the time at your destination (Td). Divide this number by the number of hours (H) that you want to transition each day (use 1 to 2.5) to determine the number of adaptation days (D) required.
D= (Tc-Td)/H
For example, if you're traveling from the East Coast of the United States (Eastern Time) to Amsterdam (Central European Time), and it's 1 PM ET (Tc) and 7 PM CET (Td), and you want to transition 2 hours per day (H), the calculation would be (1 - 7) / 2 = -3. A negative result indicates you should start waking up and going to bed earlier (“-“) than usual for 3 (“3”) days before your travel. Conversely, a positive result from the equation (no “-“) would mean delaying your sleep time for that many days.
Choosing an optimal flight is crucial and involves more than just selecting the shortest or direct route. Consider the time you will arrive; ideally, if you're flying east, you should aim to land around when you'd typically wake up in the new time zone. Conversely, if heading west, try to take off around when you usually wake, or at least so you get home around your usual bedtime. While direct flights are preferable, if making connections, plan them early in your journey when flying east and later when heading west. Timing this activity and light exposure can help ease the transition across time zones.
Regarding seating, when flying east, it's worth investing in the most comfortable seat you can afford. But be wary of splurging on business or first-class seats unless they offer lay-flat beds. If you do opt for a higher class, consider your sleeping habits; for instance, if you sleep on your right side, choose a seat to the left of the aisle to avoid your backside hanging out in the aisle (yes, there’s a story associated with this advice).
Ideally, you'll board, have a meal, and sleep through to your destination. There’s a long-hauler secret that I want to share with you. When you first get on the flight and the flight attendant asks if you will be dining with them, tell them “yes, but I would like the dine-and-rest option”. This is the option where they bring all of your food out at once and earlier in the flight, so you can sleep.
On westward flights, comfort is less critical as you’ll want to stay awake — so, you DO want a window seat if you can pick one because you will be that annoying person who keeps their window shade open (at least partially) on the flight home.
As we approach departure, it's time to acquire the four essential items previously mentioned to help adjust your sleep/wake cycle effectively.
In step 1, you determined the days needed to adjust your sleep schedule to a new time zone. Knowing your departure date, you can plan your sleep and wake times accordingly, aiming for 8 hours of sleep each night. For instance, if you're shifting your sleep schedule by 6 hours over three days, your schedule might look like this:
This schedule is quite aggressive and may be challenging to follow without a specific strategy to help you adjust. Implementing gradual changes like this can help mitigate jet lag by slowly adapting your body's internal clock to the new time zone before you travel.
Here's a diagram that visually outlines a sleep adjustment protocol used as an example earlier, using different colors to represent specific activities. To understand and implement this protocol effectively, let’s break down what each color symbolizes and how each activity might be carried out:
Each color represents a strategic element designed to optimize your circadian rhythm through natural and assisted methods, helping you to adapt smoothly to new sleep schedules or environments.
The 10-step process isn't complicated; it just requires commitment and discipline. If you understand it conceptually, you won't need to reference the diagram, and the steps will feel natural.
1. Before falling asleep, set your alarm clock for the appropriate time and put on your sleep mask. Set your alarm according to the adaptation schedule we discussed (no more than 2.5 hours per day).
2. Once your alarm goes off and the sound waves hit your eardrum, a series of events changes your brain's electrical activity. Signals from your ear travel to the Reticular Activating System in your brainstem and are then passed along to the thalamus. This triggers activity in the alerting network, causing arousal in the brain. As long as you have the discipline to get up, take off your blindfold, and get out of bed, you'll be on your way to waking up, regardless of the time.
3. **YELLOW**: I purposely set my light on the bathroom counter in my hotel room. This forces me to get out of bed and start moving. I usually stumble into the bathroom, turn on the 10,000-lumen light (which feels like flipping a switch on the sun), use the bathroom, drink a glass of water, and begin brushing my teeth. Going to the toilet, drinking water, and brushing your teeth involve coordinated movements that activate the cerebellum, activating the brain's arousal networks.
4. **GREEN**: After brushing my teeth, I get very close to my 10K light (inches away). 10K lumens is a safe brightness for the eyes, so you can look at it with your eyes open. Closing your eyes is also effective, but keeping them open is more effective since eyelids filter the blue spectrum of light, which is crucial for activating iPRGCs and inhibiting melatonin production. I look at this light for 3-5 minutes (which seems like an eternity).
**Note:** On long flights, I do steps 2-4 on the airplane. I set my alarm clock on my phone, which might wake people around me (they shouldn't be too angry; I'm helping them reset their clocks). Then, I go to the bathroom, plug in my light, and follow the steps.
5. **GREEN**: The next step is to drink some caffeine, but not a whole pot of coffee. One cup of coffee or 100mg of caffeine is sufficient to block adenosine and make you feel alert and functional.
6. ** GREEN/BLUE **: Get some activity. This might be air squats, push-ups, or something similar in my hotel room. This is not easy on an airplane, so I often skip it and wrap myself in a blanket to warm my body. The most important thing is to avoid closing your eyes and instead focus on warming your body. Contrary to common belief, this helps wake you up, as our body temperature drops when we sleep.
7. This is typically when I eat “breakfast” (regardless of what time it is). Remember, eating is also tied to your circadian rhythm. Try to eat something light but with a healthy balance of complex carbs, protein, and fat—something that won’t make you fall into a “carb coma.” Then, get on with your day. Once you're up, it's important not to take a nap. If you must nap, limit it to 20 minutes.
8. **RED**: Set your watch or an alarm clock for 3 hours before bedtime. At that time, take your melatonin (optional). This will start your bedtime preparation.
9: Do not eat or drink alcohol before falling asleep. Allow at least 6 hours for alcohol to leave your system and 2 hours for food to digest. So, you can eat when your alarm goes off and/or take your melatonin.
10. As you approach 1 hour before bedtime, darken your room (use blackout shades if necessary). Refrain from using electronic (light-emitting) devices within 30 minutes to 1 hour of bedtime. Begin your bedtime routine (shower, etc.). At bedtime, repeat step 1, setting your alarm X hours earlier. Depending on the adaptation you’re trying to achieve (set the clock back or forward), you may (BLACK) or may not (GREY) need your blindfold or blackout shades.
By understanding the neuroscience behind sleep-wake cycles and leveraging the principles of functional neurology, you can effectively manage and prevent jet lag. This 10-step process, grounded in research and personal experience, highlights how deliberate adjustments to your environment and habits can entrain your circadian rhythm to new time zones. Jet lag, a common consequence of rapid trans-meridian travel, can be mitigated by strategically using light exposure, melatonin, and other cues to reset your internal clock. Translating these neuroscientific insights into practical strategies can enhance your brain and body's ability to function as desired, ensuring smoother transitions and more productive travel experiences.
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