Circadian Desynchronisation - Jet lag

Jet lag is the desynchronisation of the body’s normal circadian cycle when crossing several meridians or time zones. To most people jet lag manifests itself as a feeling of fatigue, inability to sleep at night, loss of concentration, headaches and general tiredness.

What is Jetlag?

Circadian desynchronisation for travellers occurs after a journey across multiple time zones. A fresh environment places new influences on the circadian cycle, as the body's rhythms attempt to maintain the time cycle of the departure point. Stokes and Kite (1997) identified two distinct phenomena associated with desynchronisation. A lack of synchrony between the bodies internal rhythms and the external environment, and a lack of synchrony between the bodies various rhythms themselves.
The lack of synchrony between the internal rhythms and external environment are primarily influenced by the diurnal cycle of light and darkness. Other influences include environmental temperature cycles, eating of meals, activity and social interaction. The body attempts with some difficulty to adjust to these new influences, as the body core temperature is relatively sluggish in adjusting to a new cycle (Reilly, 1998). The body desires sleep when its temperature is lowest, this normally occurs around 3am to 5am in the morning.
Some of the body rhythms can be brought into synchronisation with the local time at approximately one hour per day, ie. if you have travelled into a time zone change which is 5 hours, it will take approximately 5 days for your body to align with the local time (Robson, 2008).

Physiology of Jet Lag

What actually underpins circadian desynchronisation is not fully understood. Hormones, including Cortisol and Melatonin, have a natural circadian cycle and play a significant role in maintaining the body's internal clock (Arendt, Aldhous & Marks, 1986). Cortisol is a steroid hormone produced in the adrenal glands. Cortisol’s functions in the body include blood pressure regulation and control of cardiovascular function. Secretion of Cortisol increases in response to any stress in the body, which causes an increase in blood sugar levels to cope with any physical or mental energy needs. Cortisol has a diurnal rhythm with a maximum level in the morning and a minimum during the night (Arendt, Aldhous & Marks, 1986).
Melatonin is a hormone that influences the desire to sleep and is secreted at night by the pineal gland. Exposure to day light diminishes Melatonin production while, darkness initiates it. Numerous recent studies suggest that the natural production of Melatonin has a direct influence on homeostasis body temperature regulation, helping to initiate sleep and amount of REM sleep that is experienced during a cycle (Buscemi, et al., 2004).

Discussion of pharmaceutical interventions

Research on the efficacy of Melatonin as a means to assist with the symptoms of jet lag has been variable. Research by Buscemi, et al., (2004) indicates that the use of pharmaceutical Melatonin in assisting with the symptoms of jet lag and as a sleep inducer has little utility. However, the highly respected Cochrane review of Melatonin noted, that it is remarkably effective in preventing or reducing jet lag, and occasional short-term use appears to be safe (Herxheimer & Petrie, 2002).

The Impact of Circadian Desynchronisation within Aviation

For individuals, the effects and symptoms associated with circadian desynchronisation are unpredictable. Experiences include disruption of sleep, gastrointestinal disturbances, decreased vigilance, lack of arousal, and lack of energy (Colwell, 1998). Long haul pilots often experience periods of drowsiness and coldness during daylight flying, as their body clocks are telling them that it is time to sleep. Cognitive effects of desynchronisation include deficits in performance, mood, motivation, and behaviour as well as, anxiety, irritability and depression (Neri, et al., 2002). Slower reaction times, defective memory for recent events, computational errors, and an inclination to accept lower standards of performance are also problems that aircrew experience as a result of jet lag.
Cho, et Al., (2000) comment that airline flight attendants suffering from chronic jet lag have higher concentrations of stress hormones and smaller temporal lobes or centres of short-term memory in the brain, than those of flight attendants that fly short haul with more regular shift patterns. It is not known whether the altered brain structure and function is permanent but, Cho, et Al., (2000) suggest that longer recovery times in flight roster patterns could reduce the problems from occurring in the first place.
With trans-meridian desynchronisation, the severity of symptoms may be worse 2-3 days after arrival than on the day after the flight. Symptoms gradually reduce as the various bodily cycles re-synchronise. The severity of circadian desynchronisation is also influenced by the direction of travel.

East West Travel

The direction of travel affects the severity of jet lag, as it is easier to cope with flying in a westward direction compared to flying eastward. The circadian rhythm is less disrupted if you fly westward. This is because while travelling westward the normal circadian cycle is temporarily lengthened and body rhythms extend in line with the normal tendency of the circadian rhythm, which is longer than 24 hours. Conversely eastwards travel has the reverse effect of attempting to compress the normal circadian cycle, in conflict with the natural, freewheeling longer than 24 hour cycle.

Circadian Desynchronisation and Fatigue

Many other factors can add to the effects of jet lag, which may initially appear to be independent of the circadian system. Stress and fatigue associated with previous work patterns and duties combined with the physiological aspects of flying exacerbate the symptoms associated with desynchronisation (Weinberg, Jantzen, & Cheyne, 1998). Indeed the effects and symptoms of circadian desynchronisation are outwardly similar to those of stress and fatigue.
Most people have few problems enduring the effects of an occasional case of jet lag; however, repeated bouts can increase overall levels of fatigue as the effects of continual circadian disruption are cumulative. Repetitive sleep disruption, combined with confused body cycles and environmental stress associated with air travel leads to a situation where chronic performance and health issues become inevitable. While fatigue and stress are regarded as separate issues to circadian desynchronisation they are intrinsically interdependent.

Strategies to Mitigate Sleep Deprivation Due to Jet Lag

To counteract the effects of Jet-lag, it is strongly advised for pilots to keep their sleeping-wake schedule as close to the same as their home time zone as possible due to the short nature of their stays. It is the timing of sleep, not necessarily the amount of sleep that is of most importance. When your body temperature is at its lowest this will promote the most restful, refreshing sleep. The amount of sleep a person achieves is also reliant on age, body type, mental activity, and individual differences (Robson, 2008).

In order to make sure of a restful nights sleep follow these measures:

  • Make sure you are sleeping in a dark and comfortable room. Having too much light can stimulate your brain and make it harder to get restful sleep, with a lower temperature and a constant flow of fresh air.
  • Try as much as possible to go to bed at the same time each night and waking up 8 hours later (where possible).
  • Maintaining a healthy weight, exercising and eating well will also aid in a more restful sleep.
  • Switch your brain off - going to sleep after excessive mental activity, or thinking about too much will cause insomnia. Try to relax by reading, playing quiet music, or meditating before bed.

As crews are exposed to rosters and time zones that dont always promote regular and adequate sleep other measures to avoid fatigue need to be taken. Another way to counteract Jet Lag is napping. Gander (2003) showed that napping is the ideal way to reduce sleepiness and it can be seen to improve cognitve performance over a longer time frame. Napping is considered the best countermeasure for fatigue and sleep deprivation besides eight hours sleep (Caldwell & Caldwell, 2003). Napping is also beneficial to crew in flight as a method of increasing performance, however due to the effects of sleep inertia should a crew member exceed 40 minutes sleep then time should be taken before making critical decisions or tasks.

In order to accommodate for changes in rhythms due to Jet Lag, the modern day 24-hour society has amplified the need, and use of stimulants (Kushida, 2005). Amphetamines, and alcohol have been used to counteract Jet Lag in the past, however they should not be used by pilots as they all promote sleep deprivation and have been marked unsafe to use when in a high risk job like flying. It has been thought that alcohol will aid sleep, though when it does induce sleep the patterns are not normal and has been shown to subdue the effects of REM sleep (Hawkins & Orlady, 1993). Caffeine has also proved to have similar effects, although this is a more safe alternative which is more widely used.

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Contributors to this page

Maria Pearson

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