Circadian rhythms are the body’s mechanism for setting a schedule. The body has a sort of internal circadian pacemaker, or clock, centered in the brain. This clock governs things like appetite and sleep, taking cues from things like sunlight and darkness. The brain likes to keep to a schedule based on this clock.
But what if your lifestyle is out of sync with your body clock? What if you need to be awake and working when your brain is telling your body to sleep? Some sleep disruptions can be traced to the clash between body clock and lifestyle. These secondary sleep disorders are called circadian rhythm disorders. Two of the most common examples of circadian rhythm disorders are jet lag and night-shift work.
A good way to understand how "stubborn" the body clock can be and how difficult it can be to adjust it is to realize that the clock also affects behaviors such as eating. Just because you all of a sudden change the hours at which you eat doesn't mean your body will automatically feel hungry at the new times. Likewise, just because you switch from a day job to a job that keeps you working until 2 a.m. doesn't mean your body will automatically adjust to your new bedtime or wake-up time.
Your circadian clock can be adjusted somewhat, but it generally takes time and consistency. If you change your bedtime, your body will likely adjust eventually, but only if you consistently stick to the new bedtime and waking time. In addition, the body seems to adjust better if the bedtime is moved later rather than earlier. As you'll learn shortly, this seems to be why, when you're traveling through time zones, it's easier to adjust if you're moving east to west rather than west to east.
Treating circadian rhythm disorders often involves a combination of chronotherapy (gradually moving the bedtime up or back) and light therapy (exposing yourself to sunlight to reset the body clock and reinforce awake time). For example, if your body wants you to sleep late in the morning but your boss doesn't, try gradually moving your bedtime up and exposing yourself to bright sunlight in the early morning to help reset your sleep-wake cycle.
Jet lag is a particularly stubborn cause of insomnia. Learn how to overcome it on the next page.