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Jet lag and social jet lag: what it is, what are the causes and its consequences in the human organism 

Sleep is essential for the maintenance of human homeostasis and repair of various metabolic, cognitive and hormonal processes. However, just sleeping is not enough. It is necessary to sleep at the right timeFRANK; HELLER, 2019Our organism is governed by rhythmic oscillations, called circadian rhythms, which oscillate approximately every 24 hours (to learn more, see https://www.condorinst.com.br/o-que-ritmo-circadiano/). Thus, several organic functions show fluctuations throughout the day, such as core temperature, melatonin concentration, physical and cognitive performance, as well as the functioning of organs such as the lungs, stomach, and intestines. Regarding the sleep-wake cycle, the body prepares to initiate sleep at night through a cascade of hormonal and neurochemical events, so that sleep obtained during the light phase of the day tends to be of poor quality and quantity. Thus, there is an ideal time for each organic function and, when there is a mismatch between the central and peripheral clocks, the organism presents a decrease in the performance of its functions. Therefore, the objective of this text is to elucidate the effects that jet lag and social jet lag have on the human organism.  

Jet lag  

Jet lag is a phenomenon that occurs when crossing 3 or more time zones abruptly, as in a plane trip, for exampleROACH; SARGENT, 2019Thus, there is not enough time for the circadian timing system to adjust to the new target location. Some symptoms caused by this condition are gastrointestinal disorders, impairments in cognitive performance, impairments in physical performance (this follows the core temperature curve, so it is extremely important that athletes pay attention to this point), excessive daytime sleepiness and insomnia at night. Because of that, jet lag is undesirable for anyone who needs to travel and maintain performance in the new destination.  

Jet lag differs from travel fatigue in that it is usually completely dissipated after a night of adequate sleep, food and hydration, while jet lag symptoms disappear only after readaptation of the circadian timing system to the new destination. Evidence indicates that, for each time zone crossed, approximately 1 day is required for complete readaptationSUVANTO; HÄRMÄ; ILMARINEN; PARTINEN, 1993Thus, it is important that the trip is planned in advance 

Some strategies can be used to speed up synchronization to the destination, but they must be considered cautiously, since each trip has a different characteristic and factors such as direction of travel (east or west), number of time zones crossed, flight duration, number of connections at the airport, time available for adaptation to the destination and direction of adaptation (whether there will be an advance or delay of endogenous rhythms)ROACH; SARGENT, 2019Some strategies that can be adopted are: 

  1. Start adapting to endogenous rhythms before the trip begins. Evidence indicates that drags of up to 2 hours are tolerable and beneficial.  
  1. When boarding the plane, adjust the time on your wristwatch so that it follows the time at your destination. Thus, the recommendation is that meals and sleep/nap times are as close to what will be performed in the new location.  
  1. Use of supplements and drugs, such as melatonin and hypnotic medications, in addition to light therapy. 
  1. Eat meals at the time of the destination. In other words, it is natural that, depending on the number of time zones crossed, there is no desire to eat at lunchtime. However, it is important to make this effort, since such temporal cues help to signal and synchronize the suprachiasmatic nucleus.  

Thus, using such strategies, it is expected that the adaptation time to the new destination will be shorter.  

SocialJet Lag 

In recent years, the term social jet lag has been coined to designate the condition of circadian misalignment brought about in everyday life. That is, it stems from the misalignment between the desired and practiced sleeping and waking timesWITTMANN; DINICH; MERROW; ROENNEBERG, 2006Similar to jet lag, symptoms include gastrointestinal disturbances, cognitive and physical impairments, daytime sleepiness, and sleep disturbances. However, symptoms are worsened by chronic exposure. A common example for this condition is individuals with an evening chronotype who need to wake up much earlier than desired to fulfill social commitments, such as study and work. On the other hand, and interestingly, individuals with a morning chronotype who express their circadian preference during work days may become desynchronized on days off, also resulting from social commitments, such as parties and meetings with friends. 

Due to the chronic content of this condition, the long-term consequences tend to be more severe. Evidence indicates that shift workers, at the end of their lives, have a higher prevalence of cancer, and this is due to both chronic sleep restriction and circadian desynchronizationHU; HARPER; HEER; MCNEIL et al., 2020Thus, the work and study routine should be, as much as possible, adjusted to the individual's chronotype. 

Conclusion 

Jet lag and social jet lag are distinct phenomena, but both are caused by circadian desynchronization. The consequences include disturbances at all levels of the organism. Thus, the ideal is that after a transmeridional trip crossing more than 3 time zones, the endogenous rhythms are resynchronized as quickly as possible and that, on a daily basis, the sleep routine practiced is close to what is desired by the individual. 

Sleep pattern assessment 

Actigraphy is a non-invasive technique that can be used to assess sleep pattern and sleep-wake rhythm. The actigraph is a wristwatch-like device that contains light, motion, and temperature sensors. Through this information, it is possible to extract data regarding variables such as total sleep time, latency to sleep onset, time awake after sleep onset, sleep efficiency, time awake and variables related to rhythm, such as cosinor, spectrogram, periodogram, and non-parametric variables such as L5, M10, IS and IV.  

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