By Daniel G. Graetzer, Ph.D.
Faculty Member, School of Health Sciences
Jet lag commonly refers to the detrimental physical and mental consequences of rapid airplane travel across one or more time zones. According to Medical News Today, the symptoms of jet lag typically include:
- Daytime sleepiness and fatigue
- An inability to stay asleep at night
- Poor concentration
- Slowed physical reflexes
- Sore muscles
- Swollen feet
- Headache
- Irritability
- Depression
- Indigestion
- Gastrointestinal problems
- Hunger at odd hours
The symptoms of jet lag generally last from two to seven days after a flight. Overall, the longer the trip, the greater your chance of developing jet lag, the worse it will be and the longer your symptoms will last.
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What Causes Jet Lag?
Jet lag symptoms are caused by the disruption of body circadian rhythms, otherwise known as your internal biological clock. The body’s day/night circadian cycles come from the term “circa dies” (Latin for “about a day”) and are synchronized to the 24 time zones on our rotating planet. Humans have diurnal (daytime) and nocturnal (nighttime) cycles in almost all biological functions, including:
- Sleep
- Metabolism
- Temperature
- Strength
- Alertness
- Heart rate
- Blood pressure
- Hydration level
- Hormonal output
Circadian cycles have various effects on the body. For example, the circadian cycles which govern the rapid early morning elevation in the hormones of epinephrine and norepinephrine probably contribute to the fact that heart attacks are three times more common in the morning than later in the day.
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Eastward Flights Present More Challenges to the Body’s Circadian Rhythm
Jet lag can also be affected by where a traveler seeks to fly. For instance, travelers on eastbound flights show a 30-50% slower re-adaptation than westward flights because it is much harder for the body to advance the timing of circadian cycles.
By contrast, westward flights delay circadian peaks and expose athletes to far fewer jet lag symptoms. Northern and southern flights that are short and stay within the same time zone enable a traveler to retain normal sleeping and eating patterns; these flights usually do not cause circadian disruption.
The control center for advancing or delaying the body’s circadian rhythms is located in a region of the brain called the hypothalamus. The hypothalamus is strongly influenced by environmental and internal time cues called “zeitgebers” (German for “time giver”). The major zeitgebers pertinent to athletic performance include diet, daylight and temperature, exercise, social interactions, and drugs.
Diet
The content and timing of foods consumed during a flight can make an airplane traveler feel either sleepy or alert and can help the body adjust to time zone changes. Consuming carbohydrates (sweet and starchy foods) provide a quick bolt of energy, but this effect is transient.
Carbohydrates stimulate tryptophan, an essential amino acid, to enter the brain. High concentrations of tryptophan are quickly converted to serotonin, a sleep-inducing hormone that makes a traveler feel tired and lethargic.
Eating high-protein foods (meat and dairy products) raises the body’s levels of the amino acid tyrosine, which results in the synthesis of the hormones epinephrine, norepinephrine, and dopamine. These catecholamines help travelers to resist sleep and increase alertness by stimulating the “fight or flight” metabolic pathway.
Recognizing that diet influences the biological clock has led to “feast-fast” and “carbohydrate-protein” nutritional manipulation techniques to help reset the body’s clock from home time to destination time. It must be remembered that dietary influences are very individual and what works for one athlete may not work and even be detrimental for another athlete.
Daylight and Temperature
Normal circadian rhythms are stabilized by exposure to daylight during the body’s awake cycle and darkness during the sleep cycle. Light flashes to the eyes and temperature signals to the skin stimulate a series of hormones that essentially tell the body it is daytime.
Exercise
Physical exertion utilizes and stimulates nearly all physiological processes. Exercise early in the day tends to reinforce circadian stability, while exercise at night works against it.
Social Interactions
Social contact tends to excite the body’s dopamine system. Ideally, social activity should be allowed during the awake phase and restricted during the rest phase.
Drugs
Prescription medications can significantly alter the body’s biological clock and should only be taken during adjusted times of the day in the new time zone. Similarly, caffeine should be restricted and used only during early morning hours and alcohol consumption should be avoided completely while the body is adapting to the new time zone.
How to Avoid Jet Lag
Taking a few simple precautions can effectively reduce the negative impact of jet lag and facilitate re-adaptation of the body’s critical circadian cycles prior to a flight. Following these seven tips from various sources has proven effective in orchestrating zeitgeber signals and diminishing the effects of jet lag and circadian disruption:
1) Pre-adapt your biological clock the week before departure by gradually shifting the lifestyle patterns in your home time zone to fit the arrival time zone. For instance, practice sleeping and eating at appropriate times in the new time zone while you are still at home.
A minimum of seven and a half hours of quality sleep every night is also advisable. Begin showering, washing your face and brushing your teeth at your usual morning time in the new time zone for five to seven days before your departure.
It is also helpful to wear two watches (one set for your home time zone and another set for your new time zone) to assist the pre-adaptation process. A rough gauge for how long it will take to readjust your circadian cycles is one day for each hour of time zone change.
2) Adjust your eating and medication patterns; diet is a critical zeitgeber to resetting your internal clock. The new diet should involve a combination of “feast” days (eating more calories than you need) and “fast” days (eating fewer calories than the body requires). Three days before travel should be “feast days,” two days pre-flight should be a “fast” day and one day before the flight is a “feast day.” The morning of a travel day should be a “fast” period with afternoon travel and all post-arrival days being “feast” times.
The timing and dosage adjustments of prescription medications can also effectively assist in time zone readjustment. Ideally, consult your private physician prior to your trip.
3) Avoid alcoholic beverages before and during your flight. Ethyl alcohol, typically found in wine and beer, is a potent diuretic that increases urine output and dehydrates the body. Before and during the flight, continually drink water and fruit juices to avoid dehydration.
Jets traveling over 200 miles will fly at about 31,000 feet and maintain a cabin pressure equivalent to 8,000 feet. High-pressure environments can cause dehydration in a flight’s passengers, which some scientists contend is a major contributor to jet lag symptoms.
Also, the cabin air for a passenger jet is heated to nearly 300 degrees, which removes all moisture before that air is cooled for cabin pressurization. Relative humidity remains about 11% in a full jet (coming solely from human exhalation and perspiration), meaning that precious moisture is continually being drawn from the body and evaporated into the environment.
Coffee, tea and other beverages containing caffeine should only be consumed immediately upon awakening in times adjusted to the arrival time zone. This adjustment in caffeine consumption is important for pre-adaptation, flight and re-adaptation. Chocolate and cocoa products should also be consumed at the right times in the new time zone; they contain theobromine, a caffeine derivative and a potent sympathetic nervous system stimulator.
4) Avoid smoking or inhaling secondhand smoke. Breathing in carbon monoxide particles multiplies any effects of oxygen deficiency that may occur while you’re flying at high altitudes. Moving around post-flight at a higher altitude than you have at home further compounds carbon monoxide’s effects.
5) Carry high-protein snacks (low-fat yogurt, cottage cheese, mozzarella cheese and crackers, granola, and nuts) onto the plane and avoid sweets. Also, chewing gum helps the Eustachian tubes in your ears adjust to the change in altitude and prevents headaches. Similarly, listening to soft music through a set of earphones can help prevent headaches.
6) Take a short jog or a walk in the early-morning sunshine during pre-adaptation and re-adaptation in your arrival time zone. If your arrival is in the morning, spend the day outside exposing yourself to local sunlight, the local temperature, and other environmental and social zeitgebers.
7) Do not attempt to sleep on a daytime flight as this sleep will further disturb your circadian rhythmicity. Wear comfortable, nonrestrictive clothing, and feel free to walk around and stretch during the flight. Wide-body jets such as DC-10s and 747s leave plenty of room to walk in the aisle and avoid muscle cramps.
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