Doctor Ellen Leibenluft describes how circadian rhythms, the 24-hour sleep-wake cycle, may be disrupted in bipolar disorder.

Circadian rhythms are rhythms in our body that alternate about every 24 hours. 'Circa’ means 'about', 'dian' means 'day' so circadian rhythms have what's called a period of about 24 hours. For a long time there has been interest in the question of whether problems in the circadian cycle or the sleep-wake cycle has something to do with what causes bipolar disorder. Certainly, we know that when people are manic or when they are depressed they have trouble with their sleep-wake cycle. When they are manic they don’t sleep and they don’t really care about sleeping, they aren’t tired. When they are depressed, particularly bipolar people who are depressed, typically they want to sleep a lot. That shows you that these problems are symptoms but it doesn’t necessarily prove that problems in the sleep-wake cycle cause bipolar disorder. The evidence that we have for that is if you take someone who has bipolar disorder and you keep them awake for all or part of the night, they have a rather significant chance of becoming manic. So we do know that these disturbances in the sleep-wake cycle can actually cause problems in the mood cycle; you can drive the mood cycle if you will by disturbing the sleep wake cycle. That’s very important clinically because some of the treatments for bipolar disorder, one of the things that they do is try to stabilize the sleep-wake cycle. It’s important for people with bipolar disorder to try to stay on a pretty regular sleep-wake cycle. For example, people with bipolar disorder may have a great deal of difficulty with shift work or with jet lag, they may have mood shifts when they suffer jet lag.

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