Generality
Jet lag or "time zone syndrome" is a physiological condition that derives from the alteration of normal circadian rhythms, consequent to the change in time zone.
In air journeys that cover long distances, the movement through at least 2-3 meridians (which correspond to 2-3 hours more or less than the usual time) can cause a partial and temporary dissociation between the perceived environmental stimuli and those of one's own biological rhythm. The organism is in fact forced to quickly synchronize its "physiological time" with the new light / dark period of the destination country.
Jet lag can induce a series of temporary disturbances, which tend to occur with duration and severity proportional to the number of time zones crossed, to the direction of the flight (east or west) and at the time of departure and arrival. The adaptation of the organism to the new biological rhythm often takes several days and is resolved by reaching complete synchronization with the destination day-night cycle.
The phenomenon is also called dysrhythmia, discronia, circadian dissonance or simply "Jet Lag Syndrome" (time zone syndrome) and is classified as " circadian rhythm disorders ".
Circadian rhythms synchronize various aspects of vital functions with periods of external light and darkness and regulate the cycle of our biological clock over a 24-hour period: the sleep / wake cycle, vigilance levels, digestion, performance, l mood, hormone levels and body temperature.
Causes
Jet lag is a chronobiological problem, similar to problems often caused by the need to work during the night or in shifts. When traveling through a certain number of time zones, the biological clock is altered with respect to the destination times and in contrast with the alternation of light and darkness to which one is accustomed.
Alteration of circadian rhythms. Jet lag can occur whenever you cross two or more meridians: passing through different time zones the circadian rhythms are no longer in sync with the new light / dark period of the destination town. The body then takes a few days to adjust its biological cycles, which include sleep-wake alternation and various other physiological functions (such as hunger, bowel habits, concentration levels, etc.).
The influence of sunlight. Our internal biological clock is deeply influenced by sunlight. The pineal gland, center of the organism's circadian organization, reacts to darkness and light: some photoreceptor cells transmit information from the retina to an area of the hypothalamus, which in turn transmits a signal to the pineal gland. Thanks to the darkness, during the night the pineal gland secretes melatonin, a hormone that regulates the circadian rhythm, in sync with the light-dark cycle: its concentrations in the blood reach the maximum between 2 and 4 am, and then gradually decrease towards the morning. Exposure to sunlight inhibits the dose of melatonin secretion.
Jet lag and hormones
Sleep disorders are linked to an imbalance in melatonin secretion.
Psychophysical disorders (which depend on circadian rhythms) are caused by an imbalance in the rhythm of cortisol, produced by the adrenal glands, which reacts to adapt to stressful external situations, such as changing the time zone; due to jet lag, circulating hormone levels tend to remain above normal for a few days. Under normal conditions, cortisol is usually secreted 2-3 times more in the morning than in the late afternoon.
Risk factors
The severity of Jet lag manifestations can be variable and depends on:
- Number of time zones crossed : the probability of developing Jet lag increases proportionally with the number of meridians crossed.
- Flight direction : Jet lag occurs only in the case of cross flights, from west to east and vice versa, and not when traveling along the same meridian (north-south). The disturbance can be felt more if you are traveling east, because you "lose" hours. The problem of Jet lag is particularly pronounced for airline pilots, crews and those who travel quite frequently. The airlines have regulations designed to combat pilot fatigue caused by Jet lag.
- Time of departure and arrival .
- Environmental factors : the reduced humidification of the environment during air travel and the limitation of movements for prolonged periods can favor the appearance of some symptoms of Jet lag.
- Individual susceptibility : age, sex and stress conditions.
Jet lag: Symptoms, Treatments and Prevention "
