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- Jet lag is a sleep disorder caused by a mismatch between the body’s circadian rhythm and the external environment. It occurs as a result of rapidly crossing several times zones and thus exceeding the limits of circadian adaptation.
- It is a benign disorder that self-resolves after a few days are spent in the new time zone.
Given its benign and transient nature, the incidence of jet lag is uncertain. In 2015 alone, 17.3 million Americans traveled to Europe and Asia, so it is likely jet lag affects several million travelers each year.
Etiology and Pathophysiology
- The circadian rhythm inherently is 24.5 hours long and is continually regulated by the suprachiasmatic nuclei (SCN) in response to external cues called zeitgebers (German for timekeepers). The purpose of the circadian clock is to regulate various hormone secretions, like cortisol, so that they are timed appropriately with regard to wakefulness and sleep (1).
- The SCN are groupings of cells located in the hypothalamus, just above the optic chiasm. These cells receive input from photosensitive cells in the retina in response to blue light via the retinohypothalamic tract. The SCN also receives input from the intergeniculate leaflet which carries information from other environmental cues that help synchronize the circadian clock such as temperature, exercise, and general excitement (1).
- Out of the above, light is the most potent and important of the rhythmic cues. This is evidenced from the difficulty blind individuals have with their own sleep cycle dysregulation; often suffering from non–24-hour sleep-wake disorder (2)
- In response to stimuli from the retinohypothalamic tract and intergeniculate leaflet, the SCN acts on the pineal gland and on the pituitary gland via the hypothalamus. Stimulation of the pituitary results in the release of various cytokines and hormones such as cortisol that promote daytime functioning. Stimulation on the pineal gland causes a release of melatonin which provides negative feedback to the SCN to promote sleep (1).
- By traveling across time zones, the circadian rhythm becomes desynchronized from local daylight hours. This change leads to a mismatch between the circadian clock and environmental stimuli.
- With time (typically 2 days for every 3 time zones crossed), the circadian rhythm adjusts to the new time zone (1).
- The biggest risk factor for jet lag is crossing 3 or more time zones. The degree and duration of jet lag is proportional to the number of time zones crossed (1).
- Eastward travel often results in a more pronounced course. This is a result of the body’s circadian clock inherently being slightly longer than a day at 24.5 hours long. Thus, it’s easier to lengthen the day, by traveling west, than to shorten it by traveling to the east because it’s more in line with the body’s inherent circadian rhythm (3).
- Age is another risk factor with the geriatric population less able to quickly adjust their circadian clock to the new time zone (2).
- In patients where the effects of jet lag may be detrimental, such as military personnel and professional athletes, light therapy prior to travel may be an option.
- For patients traveling eastward, this consists of waking up 1 to 2 hours before they normally would and exposing themselves to bright light for that period of time. The goal with light therapy is to advance the circadian rhythm to the future time zone prior to departure. Thus, the circadian rhythm will be set to the new time zone prior to arrival (3).
- Patients traveling westward should try and do the opposite and sleep in 1 to 2 hours later than normal and seek exposure to bright light in the evenings prior to departure (3).
- Light therapy should be initiated 3 to 4 days prior to departure (3).
Commonly Associated Conditions
Jet lag commonly occurs with nonspecific travel fatigue. Travel fatigue occurs as a result of long-distance air travel which results in patient experiencing prolonged periods of limited mobility, dehydration, irregular sleep times, and the effects of a cabin pressure simulating 6,000 to 8,000 feet above sea level (1).