Winter of our discontent

Out-of-sync circadian rhythms may help explain a seasonal form of depression.

- Marc Wilson

Sorry to rub it in, but I'm in an airport again. Sydney International, waiting for my connection. Apparently, it's about 7pm in Sydney, but it's dark outside and my body's telling me it's really 9pm. Next transfer is in Dubai, apparently around 6am; who knows what my circadian system's going to think by then.

Your circadian system is your internal 24-hour body clock, and when your body clock doesn't match the actual time of the place you're in, that's jetlag. Or, in technical terms, a circadian rhythm sleep-wake disorder. And it's not all in your head, either - when you're jetlagged, your body isn't producing all the right hormones at all the right times, including melatonin, which plays a role in getting you ready for a kip.

Everyone knows what jetlag feels like, even if you've spent your whole life in the same time zone. Ever stayed up a couple hours later on Friday and Saturday night because they're not work nights? Yep, that's all it takes to jetlag you. First thing I'll be doing when I'm next outside an airport is to get me some sunlight to reset my body clock.