Jet Lag

Overview of jet lag

Disturbance in sleep cycle affects nearly 150 million of the global population, as reported by National Sleep Foundation. Sleep disorders and sleep deprivation have become common among all age groups and are triggered by multiple factors like age, medications, occupation, existing diseases and at times genetic factors.A very prominent form of sleep disorder that is impacting global health is “Jet lag”. It is caused due to prolonged hours of travel especially across different time zones that results in impairment of the body’s normal sleep-wake cycle and gives rise to numerous complications pertaining to sleeplessness.

According to epidemiological studies by American Academy of Sleep Medicine, nearly 93% of travelers worldwide are suffering from jet lag syndromes. It is therefore evident that sleep disorders have become a major global health burden.

Definition of jet lag

Jet lag is a collective term for all physiological and psychological symptoms that are manifested in people traveling across multiple time zones within very short time intervals.

It is mainly observed as a disruption of the body’s normal sleep-wake and day-night cycle (medically termed as Circadian Rhythm) due to rapid switch between different time zones.

It is marked by extreme fatigue (especially daytime sleepiness), gastrointestinal disorders, difficulty in sleeping, loss of concentration and unstable mental state (irritability and depression).

Jet lag disorders are more prevalent among people traveling from western zone to eastern zone, due to loss of sleeping hours.

Causes of jet lag

Jet lag is primarily caused due to advanced or delayed sleep time while crossing different time zones. It is a result of lack of sync between endogenous Circadian Clock and the sleep-wake hours of the destination time zone. The etiological factors behind jet lag are discussed below-

• Fluctuation and maladjustment in the levels of melatonin (hormone regulating sleep-wake cycles and other physiological functions within the body) that usually reaches peak level in blood at around 2 AM (according to local time zone)
• Crossing multiple time zones within a very short period of time
• Frequent exposure to change in time zones mainly due to occupational requirements
• Travel headed to east ( due to considerable shortening of the day length )
• Complete loss of sleep during the entire time of travel
• Exposure to bright light (illumination within aircraft or sunlight) during an inappropriate time of the Circadian Cycle (due to re-adjustment of the normal Circadian Rhythm)
• Lack of adaptability to Circadian Misalignment (mainly due to age)
• Lack of physical fitness to adjust to changes in sleep-wake cycles or extreme sensitivity to change in time zones
• Dehydration-induced by very high environmental temperature (of destination)
• Shortage of oxygen in the body due to reduced pressure at very high altitudes
• Lack of adjustment with cabin pressure and low humidity within the aircraft (causes dehydration)
• Deterioration of body’s resistance to fluctuations induced by external environment due to age or existing diseases

Pathophysiology of jet lag

The main contributing factor behind jet lag is the melatonin hormone which controls the Circadian Rhythm of the body and associated physiological functions.

Melatonin is released during the night (solar dark hours) causing dilation of peripheral blood vessels and a subsequent drop in body temperature.

Melatonin level in the blood normally reaches the maximum level during 2 AM.

Therefore during a change of time zones readjustment of the internal body clock becomes necessary to attain the peak level at the same time according to the local time zone of the destination.

But this fails to happen because Melatonin secretion is inhibited by bright light, which a traveler is frequently exposed to (at the wrong hours) during the transition between different time zones. This leads to series of jet lag symptoms.

Symptoms of jet lag

Jet lag is manifested as a series of co-related symptoms which are more prominent after completion of the entire travel period. They can vary from mild to severe, depending on the clinical state of the body. Following are the commonly observed jet lag symptoms.

• Acute insomnia due to disturbed sleep cycle at night
• Drowsiness during the daytime which mostly results from loss of sleep at night
• Extreme fatigue and overall weakness
• Gastrointestinal disorders like constipation or diarrhea
• Mental instability causing frequent mood swings, depression, and irritability
• Cognitive impairments leading to loss of concentration or inability to perform normal activities
• Reduced alertness caused by disturbed melatonin secretion
• Loss of appetite
• Muscle cramps and overall body pain due to incorrect sleeping postures during the entire time of flight
• Nausea and vomiting
• Persistent headaches

Types of jet lag

Jet lags can be of two types based on the direction of travel (east to west/west to east)

• Eastward travel: Eastward travels have more chances of inducing jet lags because a virtual shortening of the overall day-length occurs, causing loss of sleeping hours. The main difficulty observed after traveling 6-9 hours towards east is that the local morning time may wrongly coincide with the phase of the body cycle preceding that particular phase. In this case, the internal body clock normally adjusts via a phase delay (disadvantageous as compared to phase advance). This is triggered by melatonin secretion and exposure to bright light during inappropriate timings of the day (that contradicts the normal Circadian Cycle).
• Westward travel: During westward travel, the body clock adjusts via phase advance that is more evident during the extended first day of travel. In this case, a short nap is essential during the initial hours of the travel that prevents sleepiness during odd hours of the day (due to homeostatic effects).

Treatment & Prevention

In order to prevent jet lag from occurring, try to get as much sleep as possible during the flight. Use ear-plugs and eye masks to ensure you get uninterrupted sleep.

If you are taking an east-bound flight, try waking up few hours earlier everyday and do the opposite if taking a west-bound flight.

Refrain from consuming alcohol or caffeine on the day of travel, as these substances interfere with natural melatonin production of the body can hamper sleep during and after the flight.

In order to treat jet lag symptoms, it is important to synchronise your body’s cycle with the natural daylight. Try to get as much sunlight as possible to naturally reset your body’s circadian rhythm. Few OTC (Over-The-Counter) melatonin supplements can also help with this condition. Upon reaching the new time zone, try to take your meals at regulated hours so that your body starts adjusting to the new time schedule. Always get a full night’s sleep before and after your extended journey.

Typically the vulnerable groups of jet lag are people traveling across different time zones due to professional requirements (flight attendants, pilots, athletes, businessmen). National Sleep Foundation has formulated different diagnostic techniques to completely assess jet lag such as- maintaining sleep logs, Actigraphy and Polysomnography. Certain therapeutic measures proposed by doctors worldwide have also proved to be effective in coping with jet lag syndromes and associated complications.

References