Jet lag is nature's way of making you look like your passport photo. -Linda Perret

It used to be that sailing ships, and later liners, went through time zones at a stately pace so that everyone had time to adjust.

In the early days of flying the large number of stops between, say, England and Australia, forced a regime of rest, fly, rest. Now we can fly to almost anywhere in Europe with one stop. Under those conditions jet lag can possibly, probably, certainly set in.

It is caused because on long travel sectors, such as London to Sydney, you fly through ten time zones. The result is that the natural body rhythm which tells us when to wake up, when to eat, when to go to the loo, is thrown totally out of synchronisation.

The end results, depending on the age and the metabolism and the experience of the passenger, can be pretty horrendous. In the section on stress the evidence is that eight trips a year which put you through jet lag makes it fairly certain you are going to be ill. A point seriously worth pondering.

Why is this? Our bodies, and to a certain extent our minds, are carefully and fairly rigidly set to a 24-hour clock which keeps pace with the seasons. In any 24 hours there is a series of biological functions that follow a reasonably precise timetable. Jet lag sets this all on its heels, so our body knows not whether it is Arthur or Martha.

Your circadian rhythm - the internal metronome that tells you when to sleep, when to wake, when to work, when to take it easy - is thrown out of kilter because your senses are sending signals that it is light when it should be dark and so on. The body and the brain takes a long time to get over this.

The problems are demonstrated physically, through signs such as heartbeat and temperature. The mental recovery rate is very similar to the physical recovery rate. The problem does not occur if you stay in the same time zone, no matter how far you fly.

What can be done about it?

There is, as yet, no sure and certain cure-all. But there are some actions you can take which will act as a form of limited damage control and help you recover quicker.

Work on the general basis that your body needs 24 hours to recover for each two hours of time shift. No time shift, no recovery period. This you may find strange.

If you fly London to Johannesburg you suffer no jet lag penalty. But change that to London to New York and you are suddenly in deep strife.

Jet lag affects your judgment. Many companies now have a rule that business executives may not make a business decision until they have had a full 24-hour rest period. This seems pretty sensible.

My own view is that if I am abstemious with food and drink, if I do some gentle exercise, if I select a flight with the least possible number of stops - preferably just one - and if I try to remain awake during the daylight hours of my first day, on arrival, I shall be reasonably under control.

A few years ago I conducted a seminar in Melbourne on a Thursday and Friday, in London on the following Monday and Tuesday and in Amsterdam on that Thursday and Friday. Afterwards I came down with what, at the time, I thought was virulent flu. Now I am quite certain it was my body screaming out for rest.

As I write this I am, yet again, in London. I have just flown in from Thailand on a non-stop flight. I am writing this at three o'clock in the morning because I feel awake and alert. This afternoon I shall get my head down and sleep. By thus adjusting my work schedule I will cope with jet lag, but I do not fool myself that I have conquered it.

These are the limited steps you can take which may, just may. make it easier on yourself.

" Melatonin, an over-the counter product in the United States but not, I think, in Britain or Australia. It has been called the new miracle jet-lag pill.

A fellow journalist swears by it. He thinks that if it is taken in the morning, it delays your body clock and allows you to stay up later. On the other hand, if taken at night, it encourages sleep. That is his experience but he is a strange chap.

I have taken it and gained nothing but quite dreadful nightmares involving bank managers and worse things I could mention. It has apparently been successfully tried out on sheep. I know of no sheep with frequent flyer points. After trying it several times at night, I found that my sleep was still irregular, although deeper, but my dreams more bizarre.

" Do not drink alcohol while you fly. This may, indeed, be a counsel of perfection, but it is demonstrable that drinking while flying throws an intolerable strain on your ability to adjust.

" Exercise. This is not easy. I do yoga every other hour on board the aircraft. On several occasions I have been approached by solicitous flight attendants worried that I was in pain. This worries me not. I would rather look silly than suffer.

" When you arrive try not to go to bed; stay awake until night-time.

" Get out in the sun. Or use an artificial substitute. Sunlight is, for me, the best cure. Give me three hours of sunshine and I am fine. Going to Wales this causes me problems.

" Where possible break your flight. I would never now dream of flying direct Sydney/London unless my nearest and dearest was in severe strife. Instead, I get off at Bangkok or Singapore or Hong Kong and give my body a chance to recover.

" Remember that carbohydrate meals make you sleepy and protein meals keep you awake. Eat accordingly.

" Do not take pills of any sort if you can help it. In my experience, and that of most other travellers, it merely postpones and amplifies the agony.