Although you won’t hear it tick, your body has its own clock. The physical and mental changes it causes are called circadian rhythms. Most living things have them, including animals, plants, and even some germs.
Circadian rhythms affect your sleep patterns as well as other ways your body works, like your hormones, body temperature, and eating habits. When they get out of sync, they might also cause problems with your health. They’ve been linked to different disorders including diabetes, obesity, and depression.
To get good, healthy sleep, it helps to know what keeps your body’s clock on track and what might throw its rhythm off.
How Circadian Rhythms Work
About 20,000 nerve cells make up your “master clock,” a part of your brain called the suprachiasmatic nucleus. This structure, which sits inside an area called the hypothalamus, controls your circadian rhythms. While largely guided by your genes and other natural factors inside your body, things in the outside world can also alter them.
The biggest cue is light. Your body is wired to sleep when it’s dark and stay awake when it’s light outside. Nerves directly link your eyes and your body’s master clock. When daylight fades, your eyes signal your brain to make more melatonin, a hormone that makes you feel sleepy. And when the sun rises again, the signals tell the brain to turn down the melatonin.
Different Patterns for Different People
You’ve likely noticed that you feel more alert during certain parts of the day and have lower energy at others. This pattern has to do with your “chronotype,” or personal circadian rhythm. They vary from person to person, although they tend to run in families.
Most of the time, people fall into one of two groups:
Early birds: If you find it easy to wake up in the morning and feel you have the most energy early in the day, you’re a morning person or a “lark.” Some research suggests that an early bird’s body clock may run slightly faster than 24 hours.
Night owls: If you’re an evening person, some research suggests that your body clock runs slower than 24 hours. You’ll find it hard to wake up in the mornings and feel alert. You’ll have the most energy much later in the day, like 11 p.m.
Your chronotype isn’t set in stone, though. Circadian rhythms naturally change as you age. For example, the body clock shifts during adolescence, making teens want to go to bed later and sleep longer than younger kids.
Your work or school schedule may mean that you need to switch from a night owl to an early bird. You can try to alter your circadian rhythm yourself, but do it slowly. For example, try waking up 15 minutes earlier each morning over the course of a week.
Circadian Rhythms Out of Sync
Small changes can upset your circadian rhythms. These include:
Extra sleep. Your body clock works best when you stick to a schedule. In an ideal world, you’ll go to sleep and wake up within a half hour of the same time each day, even on weekends.
Travel. When you pass through time zones, you can adjust your watch but not your body clock. It will try to function on the time it is at your home, a problem you may know as jet lag. The more time zones you pass through, the more off you may feel. Your body clock will reset to the new time you’re in, but it can take a few days.
Screen time. Any amount of light signals your brain that it’s time to be up and alert. Even the blue light from your tablet, smartphone, or TV has this effect. To get a good night’s sleep, unplug from all screens 2 to 3 hours before bed. Other artificial light can have the same effect, so turn off hallway lights and face your alarm clock away from you. If you’re bothered by light outside your home, put up blackout curtains or use a sleep mask.
Night shifts. If you work nights, you’ll need to sleep during the day. This can be tough since your body is programmed to be awake when it’s light outside. Over time, you can start to have what’s called shift work disorder. You’ll find it hard to stay awake at night, yet struggle to sleep during the day. Naps during the day or your night shift can help.
Your period. Many women notice that they sleep worse before their period starts. This may be due, at least in part, to a change in circadian rhythms. Some studies show that less sleep during this time can reset your body clock and give some relief. Bright daylight or light therapy may also make a difference.