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Jet lag presents a significant challenge for travellers, especially when crossing multiple time zones. A term given to passengers who suffer from symptoms such as fatigue, headache, irritability, sleeplessness, daytime sleepiness, inability to sleep at night, and changes in their daily routine following air travel, jet lag happens when one travels in five or more time zones, either eastwards or westwards. This may occur during the flight or after the flight. Jet lag is more common in elderly people than younger ones. The symptoms differ amongst individuals. A period of about 24 hours is referred to as the circadian rhythm. Numerous physiological and psychological factors in humans, such as core body temperature, cortisol levels (the fight-or-flight hormone), blood pressure, heart rate, hunger, subjective alertness, subjective sleepiness, and objective sleepiness, have been demonstrated to change regularly in less than a day.
Circadian rhythm
A central circadian pacemaker housed in the suprachiasmatic nucleus of the hypothalamus is responsible for producing endogenous circadian rhythms in physiological and psychological aspects of human behaviour. The environmental cues known as zeitgebers, or time givers, entice these rhythms over a full day and night. The body's three main organs — the liver, heart, and lungs — also have circadian oscillators.
A discrepancy between departure zone time and the circadian rhythm, or internal body clock, results in jet lag. The body's natural circadian rhythm, or internal body clock, cannot quickly acclimatise to the new time zone's light. The results of this desynchrony include jet lag symptoms. Instead of aligning with the zeitgebers at a new place, the circadian system first aligns with those at the point of departure. The brain's pineal gland is the primary source of the hormone melatonin. It contributes to the circadian rhythm and sleep-wake cycle. In the absence of light, the pineal gland releases the most melatonin. Because of the relationship between human sleep/wake cycles and circadian rhythms, endogenous melatonin production starts around two hours before typical bedtime. Seven hours following melatonin onset, the daily minimum core body temperature rhythm takes place, which corresponds with the daily low point of the circadian cycle. The minimum core body temperature is at 0400, while melatonin onset is at 2100 if a person typically sleeps from 2300 to 0700.
Direction matters
The direction of travel affects jet lags. Flying in an easterly direction produces more symptoms than flying in a westerly direction. This is because travelling west 'prolongs' the body clock's experience of its normal day-night cycle (the normal tendency of the body clock in most of us is slightly longer than 24 hours). Travelling eastwards, however, runs in direct opposition to the body clock.
Countering the effects of jet lag
Nothing is required if the travel zone time for planes heading east and west is less than three hours. You must modify your sleep schedule if the travel time zone is three to six hours. Severe jet lag symptoms may arise from travel time zones that are 12 hours or longer apart. The following is suggested: As soon as you get at the eastward station, expose yourself to artificial and blue light. Commercial blue lights are available. This promotes the synthesis of melatonin. Before travelling, melatonin can be started at least 11 hours before the minimum time required for the core body (500 mg every three to four days) for three to four days starting at 3 pm local time. There is no need for a prescription for this over-the-counter drug. Three to four days before your trip, adjust your sleep routine based on the time zone you're going to be visiting, not your current one, and walk for at least 40 minutes each day until your biological clock is adjusted.
(The author is the Group Captain (Rtd) and aerospace medicine
specialist, Indian Air Force)