Changing Time Zones: The Health Effects of Jet Lag

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As a human race, we have only been able to cross such large distances and multiple time zones in the past century. Before commercial flights were a common way of travelling overseas, we would have been able to cope with changing time zones better during a lengthy voyage by sea.

Besides the lack of hydration, uncomfortable seating position and questionable food we are subjected to during an economy flight, the main reason why jetlag catches up on us is to do with our circadian rhythm being desynchronised. Until we evolve to adapt to frequent travel between time zones, this cannot be ignored.

A lot of our body’s physiology is regulated by neurotransmitters that can be classified as amino acids, peptides and monoamines. One example of a monoamine is melatonin, which is affected by sunlight over a 24-hour period (circadian rhythm). A disruption in this circadian rhythm can profoundly affect body temperature, digestion, heart rate, blood pressure, hormones and state of mind (source –The State Government of Victoria).

Naturally corresponding with the amount of hours in the day, there 24 time zones around the world. It has been documented that travelling over two time zones will have a marginal effect to a person’s circadian rhtyhm but travelling over any more than three can cause desynchronisation to a substantial degree (source – Reilly T).

The Effects

Travelling west will also make jetlag easier to recover from due to the circadian rhythm being temporarily prolonged to about 27 hours, making it easier for the body to adapt (Reilly T). When experiencing a shift of any more than 12 time zones however, travelling east or west does not make a difference. That would be the equivalent of flying from Adelaide to Sao Paulo, Brazil. It would be hard not to pull up a bit rough after a marathon flight such as that.

After travelling east, it is also common for people to have trouble getting out of bed at a normal time in the morning while flying back from the west will result in waking up before dawn (Libassi L, Emad YA).

Suffering from jet lag may be inconvenient for someone coming back from a holiday or the occasional business trip but it can have further implications for those travelling more regularly as a part of their day-to-day lifestyle.

According to Centers for Disease Control and Prevention (CDCP), the amount of days jet lag could last for can be calculated.

In the United States, where sporting teams could experience up to four different time zone changes on a flight to an away game, the overall effect of disrupted circadian rhythms to the whole team can impact results and change the course of a season.

A three-year study on 19 North American Major League Baseball (MLB) teams found the home team could expect to score 1.24 more rune than usual when the visitor had just completed eastward travel. Home teams also scored 0.62 more runs during the day than the night (source – Recht LD, Lew RA, Schwartz WJ).

A more recent 10-year study found MLB teams that travelled through three time zones have as much as a 60% chance of losing their first game upon arrival (Winter WC, Hammond WR, Green NH, Zhang Z, Bliwise DL).

Jet lag can no doubt take its toll for sporting teams and businessmen who must travel as part of their job but there usually is a period of rest for the body to recover from crossing multiple time zones. Cabin crew members on international flights regularly do this more than anyone with as little as two days break before their next flight.

A study on 62 experienced female cabin crew members found increased secretion of the stress hormone, cortisol, and impaired nonverbal cognitive processing for cabin crew members who travelled on more transmeridian flights with less days off. The results showed the body could not even adapt to the stress of jet lag with some participants having as much as four years experience in the field (Cho K, Ennaceur A, Cole JC, Suh CK).

Another study on 45 female flight attendants and 26 teachers confirmed the variability in melatonin production as high as 25% was twice as likely to be associated with flight attendants (Blosser F).

The Treatment

As mentioned previously, melatonin is a key factor for regulating sleep. It also promotes the release of antioxidant enzymes and can act as a defense against free radicals (Rodriguez C, Mayo JC, Sainz RM, Antolín I, Herrera F, Martín V, Reiter RJ).

Available as a 2mg prescription tablet in Australia, melatonin can help combat jet lag easily and with minimal side-effects. Although, the Therapeutic Goods Administration does not advise taking melatonin in combination with alcohol, Thioridazine and Imipramine, and benzodiazepine or other hypnotics.

Nine out of ten randomised trials on airline passengers, airline staff and military personnel crossing five or more time zones saw decreased jet lag symptoms in subjects when melatonin was taken one hour before the destination bedtime (10pm to midnight). Doses of melatonin closer to 5mg were seen to be significantly more effective than a slow-release 2mg dose (Herxheimer A, Petrie KJ).

Adjusting to a new time zone before arrival, known as preentrainment, can be another way of dealing with jet lag. This is to do with our chronosense, a biological response to light generated by the suprachiasmatic nucleus that can be active even in blind newborn babies (Sernagor E).

A study on 28 participants trialled a three-day treatment of exposing differing amounts of light in the first 3.5 hours of waking, advancing normal wake time by one hour each day. Participants who received the greatest amount of bright light over the three days experienced a phase shift of nearly two hours, which can be particularly helpful for those travelling east and arriving in the morning (Burgess HJ, Crowley SJ, Gazda CJ, Fogg LF, Eastman CI)

The disadvantage of this treatment is the inconvenience of being exposed to bright light and still carrying out normal morning duties.

Another study from the same research team combined morning bright light exposure with afternoon doses of melatonin over three days before a flight. Participants experienced a phase advancement of nearly 2.5 hours and no jet lag symptoms with a 0.5mg dose of melatonin and alternating exposure of bright and dim light for 30 minutes (Revell VL, Eastman CI).

Previously, the typical method of dealing with jet lag would be drinking yourself to sleep on the flight followed by a stupendous amount of coffee consumed on arrival. The health implications of these methods are obviously detrimental. Until we make genetic advances to cope with jet lag however, the other options available today are safe and effective for returning back to your regular time zone.
Images courtesy of visual.dichotomy, Will Fisher and Wikimedia.