Number 44, 2009
Circadian rhythms and cardiovascular disease

Jet lag

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Graham Jackson
Guy's and St Thomas’ Hospitals NHS Trust, London, UK
Correspondence: Graham Jackson, Suite 301 Emblem House, London Bridge Hospital, 27 Tooley Street, London SE1 2PR, UK.
E-mail: gjcardiol@talk21.com

Case report
The time in Bermuda is 4 hours behind that in the UK, and traveling westwards from London takes 7½ hours. Using my British Airways Air Miles, my wife and I flew first class return, obviously in comfort. I am always cautious regarding avoiding dehydration (1 litre of water for every 5 hours flying time) and excess of both alcohol (wine only) and caffeine (avoided). Traveling west I do not sleep, but traveling east – as long as it is a night flight – I settle down as soon as is practical. On this occasion, we left London at 15.00 h, arriving on time at 18.30 h local time (22.30 h UK time). The travel fatigue that is associated with any long journey was not evident (comfortable travel, excitement on arrival) and our hotel was reached at 20.15 h. A quick “freshening up” was followed by dinner on the restaurant terrace, where we were greeted warmly (our fourth visit – nice to be recognized). A relaxing meal, good wine, and bed at 22.30 h. Awake at 03.00 h (why is it always 3 a.m.?) and grateful for the in-room filter-coffee maker at 05.00 h. A lazy day by the pool/beach followed, with slight fatigue only. Sleep disturbance persisted for 4 days, in spite of our taking no caffeine after 17.00 h (tea). The holiday was very enjoyable, with good weather, and very relaxing. Seven days later, we left Bermuda at 20.00 h, arriving back in London the next day at 06.30 h local time. A smooth and excellent flight and 2 hours’ sleep. The rest of the day was spent dealing with emails and the post, and checking with my secretary about the week's events – from home, as planned – keeping going as long as possible to try to get back on UK time, bed at 22.30 h, and a complete night's sleep to 06. 00 h. No further symptoms or problems. Unusually, I had experienced far more sleep disturbance going west than east. In contrast, traveling east my wife adjusted after 1 day only, and traveling west 2 days of fatigue slowed her – we are all individuals where jet lag is concerned.

Discussion
Jet lag is a result of the body clock not being adjusted to the new time zone [1]. The rhythm most affected is sleep. As the body clock adjusts, jet lag resolves. As the number of time zones crossed increases, so the severity of the jet lag increases, with flights to the east more affected than those to the west. The world is divided into 24 time zones based around the Greenwich meridian in the UK, and the time changes by 1 hour for every 15 degrees traveled in either direction. Traveling over three time zones increases the risk of jet lag. Flying east, the body finds it more of a challenge to adjust to a longer day, so jet lag lasts (in days) for two-thirds the number of time zones crossed traveling east, compared with approximately a half the number traveling west. Speeding up the time frame may help prevent or reduce jet lag.
The best way to alleviate jet lag is to adjust the body clock to maximize the synchronization of the circadian phase to the rhythm of light and dark at the destination [2]. Traveling west, it is helpful to stay awake as long as it is light; traveling east, staying awake (avoiding bright light in the morning) and being out and about as much as feasible in the afternoon are to be recommended. Melatonin secreted by the pineal gland is turned off by light, and this pattern of behavior is designed to turn it back on naturally at the correct time: the release of melatonin is associated with it being time to sleep. Advice on general issues is summed up in Table I.

Table I. Advice for coping with travel fatigue.

Summary
If a journey crosses fewer than three time zones, jet lag is unlikely to be significant. If the time away is fewer than 3 days it is advisable to try to keep on your home time. If the journey is more than three times zones, jet lag can be minimized by using light to promote body clock adjustment, taking melatonin to help with clock adjustment and sleep, and keeping alert during daytime (caffeine of your choice – mine's a cappuccino!).

Personal note
We were in the sky traveling smoothly at exactly the same time as the Air France flight was, tragically, not doing so. At times like these, we can only reflect on our vulnerability and offer sincerest condolences.

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