Generality
Jet lag or "time zone syndrome" is a physiological condition that derives from the "alteration of normal circadian rhythms, consequent to the variation of time zone.
In air travel covering long distances, the movement through at least 2-3 meridians (which correspond to 2-3 hours more or less than the usual time zone) 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, the direction of the flight (east or west) and the time of departure and arrival. organism at the new biological rhythm often takes several days and resolves itself by reaching complete synchronization with the day-night cycle of the destination.
The phenomenon is also called dysrhythmia, dyscronia, circadian disynchronosis or simply "Jet Lag Syndrome" (time zone syndrome) and is classified among the "circadian rhythm disorders".
Circadian rhythms synchronize various aspects of vital functions with external periods of light and dark and regulate the cycle of our biological clock over the course of 24 hours: the sleep / wake cycle, levels of alertness, digestion, performance, "mood, hormone levels and body temperature.
Causes
Jet lag is a chronobiological problem, similar to problems often induced by the need to work during the night or in shifts. When traveling across a number of time zones, the biological clock is altered with respect to the destination times and in contrast with the alternation of light and dark that one is accustomed to.
Alteration of circadian rhythms. Jet lag can occur whenever two or more meridians are crossed: when crossing different time zones, the circadian rhythms are no longer in sync with the new light / dark period of the destination location. The organism therefore takes a few days to adjust its biological cycles, which include alternation between sleep and wakefulness and various other physiological functions (such as hunger, intestinal habits, concentration levels, etc.).
The influence of sunlight. Our internal biological clock is deeply influenced by sunlight. The pineal gland, the center of the organism's circadian organization, reacts to darkness and light: some photoreceptor cells transmit information from the retina to a area of the hypothalamus, which in turn transmits a signal to the pineal gland. Thanks to the dark, during the night the pineal gland secretes melatonin, a hormone that regulates the circadian rhythm, in synchrony with the light-dark cycle: its concentrations in the blood reach a maximum between 2 and 4 am, and then gradually reduce towards the morning. Exposure to sunlight inhibits melatonin secretion in a dose-dependent manner.
