Monday, January 17, 2011

Jet lag

With certainty, human beings never travelled much more than 10 km in a day throughout human evolution. Even 30 years ago, you could easily find adults who had never been in a plane in their life. Now, I have children in their early 20s who have been to more countries than I have.

In 1966 I was booted out of London and sent off to live in Adelaide, South Australia. The flight was London, Frankfurt, Athens, Cairo, Karachi, Singapore, Sydney, Melbourne, Adelaide. That’s eight legs for a flight that has two legs now and only one in 2020. I don’t recall getting jet lag, probably because the trip took so long (you disembarked and pfaffed around at each airport; no shopping malls).

Circadian disrhythmia

Travelling across time zones now is rapid and will upset your circadian rhythm (from circa diem, Latin for “about 24 hours”). More than 300 bodily functions occur with a 24 hour rhythm. These functions normally have “high” and “low' points during the 24 hour period, corresponding to a sleep-wake cycle. For example, body temperature, (which peaks at around 6 pm), heart rate, (which is higher in the afternoon), and the stomach, (which empties a little more quickly in the morning than in the evening) all have a circadian rhythm.

Adjusting body clock

When travelling across time zones, some people adjust their body clocks to their destination time in the two or three days before departure. On arrival they can quickly adopt local times for eating and sleeping. This can be very effective when crossing 1-4 time zones. For example, if you are travelling east, gradually get up earlier each morning so that you are 1-2 hours “closer” to your destination time zone.

Getting sunlight early in the morning also helps this transition. Do the reverse if you are travelling west. Adjust to getting up later before you leave and expose yourself to bright sunlight in the evening if possible so that your body feels like it is closer to your destination time zone.

Anything you can do food-wise?

Yes, but it is going to sound a bit obvious. Some folk pre-order a vegetarian or low-fat dish, not because they are necessarily vego or weight conscious, it’s just that the “special meals” are often better quality. Besides, fatty meals can make you feel a bit gluggy. It’s not as if you can go for a long walk afterwards to feel more normal.

The humidity in aircraft is around 10-15%, which means that moisture is lost from your body a bit quicker than normal, estimated at an extra 20-25 mL per hour. I have read that new aircraft will have a higher humidity because anecdotal feedback has been that people experience less jet lag at a more normal humidity of 25-30%. Anyway, this is the reason you are told to “keep up your fluids” when flying. That includes tea and coffee (caffeine does not cause excessive fluid loss), water and juice.

It doesn’t include alcohol. I don’t drink alcohol on flights for two reasons: 1) it is dehydrating; and 2) my wine tastes dreadful in a dry atmosphere from a plastic cup (yeah, I know, you travel business class and get a very nice red in a glass, so it doesn’t apply). One advantage of having a beer or wine with your airline meal is that alcohol reduces platelet aggregability so blood is less sticky and you have less chance of deep vein thrombosis.

What does it all mean?

Most people jump on a plane, cross a few time zones, then cruise straight into local time. That’s probably the best you can do when crossing four or more time zones and on holidays. With three or less time zones, I like to pre-adjust my body clock in the preceding days at one hour a day, especially for easterly travel. When you arrive, immediately adopt the local time, try not to nap during the day to catch up sleep, and sleep in a cool bedroom. It can be helpful to go for a walk three hours or so before bedtime for a more restful sleep. Despite all the theories, the best cure for jet lag is still time. I think that being fit and eating sensibly helps.

Final tip – get to the airport early. The last thing you want to get is a middle seat. Sorry. Forgot. You travel business class.

Reference: Journal of Sports Sciences 2007; 25 (S1): S125-S134

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