sleep foundation
The National Sleep Foundation

Medically Reviewed by

The National Sleep Foundation

Written by

The National Sleep Foundation

Reflecting the sun’s natural movement in a 24-hour orbit around the earth, your body’s circadian rhythm has a 24-hour cycle. Over the course of those hours, your energy levels grow and drop multiple times, making you feel wired at certain points and sleepy at others.  But your circadian rhythm doesn’t operate in a vacuum—it is guided by variables including light exposure and your mealtime schedule.  And that’s good news since these are factors you can alter, thereby gaining some control over your internal clock.

The Time Zone Effect

You’ve probably already altered your circadian rhythm before without even trying. Think about the last time you traveled to another time zone. Within a week or so, your circadian rhythm is in sync with the new time—you know this because you are falling asleep at an hour when you used to wake up. (Of course, you have likely also experienced the fallout from an internal clock that is not capable of adjusting quickly enough to drastic time shifts, resulting in insomnia, crankiness, and confusion for your first few days abroad.)

Making the Switch

Travel isn’t the only reason you might want to change your circadian rhythm. Maybe you have a new job with different work hours or signed up for a pre-work gym class. To adjust your sleep hours, the biggest tool at your disposal is light (or lack thereof). When it’s dark outside, your brain naturally signals to your body to release melatonin, a hormone that makes you feel sleepy. When it’s light outside, your brain sends a signal to cut off the melatonin supply, making you feel more awake.  To shift your circadian rhythm earlier, dim the lights in your home an hour before bedtime to prepare yourself for sleep. As soon as the alarm goes off, turn on as many lights as you can to simulate a bright sunny morning.

Other Strategies

Your circadian rhythm responds well to light cues, but other aspects of your daily life can influence it as well. For instance, the time of day you eat can speed up or delay your internal clock. If you shift your breakfasts, lunches, and dinners to later in the day, this may also move your body’s internal clock back,  making a later bedtime feel more natural. Another variable: Your exercise routine. Hitting the gym in the evening instead of the morning can shift your circadian rhythm later as well.

Whatever strategy you follow, it’s best to make the changes in small increments. Move your plans 15 minutes earlier or later each day until your find a rhythm that works for you.