Why does jet lag feel worse travelling from west to east?

"West is best, east is a beast" the saying goes, and most travellers agree. When you travel in an easterly direction, the jet lag is a whole lot worse than travelling the opposite way. That's bad news for Australians travelling home from Europe or heading to the US, and science researchers have come up with some ideas that explain this phenomenon.

For most of us, research suggests, our circadian rhythms – the internal sleep/wake clock that tells us when to sleep and when to get up – are slightly longer than 24 hours. We find it easier to stay up an hour past our bedtime than we do to get up an hour earlier in the morning. Therefore, travelling west, and coping with a later sleep/wake time than at home, comes more naturally than travelling east and hitting the sack earlier.

The main cue that helps regulate our body clock is morning light, which tells us when it's time to get out and start hunting, harvesting or sightseeing. Exposing yourself to morning light at your destination is critical, although other research also suggests that you can only expect your body clock to adjust by about two hours per day.