What is circadian rhythm? Plus, why it’s essential for better sleep

sleep

Oct 10

Written By Calm Editorial Team

Clinically reviewed by Dr. Chris Mosunic, PhD, RD, MBA

Think of circadian rhythm as your body’s master clock. Discover how it affects your energy and sleep, and 10 simple ways to support it every single day.

You know those days when your energy feels completely out of sync with your schedule? Somehow you’re exhausted by 3pm and then inexplicably wired at bedtime? Or you finally get into bed but find yourself awake, staring at the ceiling? These may not be random off-days — they could trace back to a disruption in your circadian rhythm.

Your circadian rhythm is your body’s internal clock. It plays a key role in regulating when you feel alert, when you start to wind down, and how your energy shifts throughout the day. When it’s stable, sleep tends to come more naturally. But when it’s thrown off—by late nights, travel, stress, or an irregular schedule—your whole system can feel out of step.

If you feel like your circadian rhythm’s off, here’s the good news: you can fix it. We'll break down some simple ways to sync up with your body’s natural rhythm, and why it matters for both sleep and overall wellbeing.

What is circadian rhythm?

Circadian rhythm is your body’s natural 24-hour clock. It helps decide when you feel awake, when you get sleepy, and even when your body does its behind-the-scenes work like repairing cells or balancing your hormones. The word “circadian” comes from the Latin words “circa” (about) and “diem” (day), which roughly translates to “about a day.”

Since circadian rhythm works in a 24-hour cycle, it’s important to note that everyone’s rhythm isn’t the same. For instance, some people feel most alert in the morning, while others find they’re more awake at night. The reason for this is that factors like genetics, age, and lifestyle all play a role. And because your circadian rhythm is flexible, your rhythm can shift with life changes like new jobs, travel, or just a different routine.

Why does your internal body clock matter?

When your circadian rhythm is steady, your body runs more smoothly. Sleep feels restorative, your energy fits your daily demands, and your mood and focus are more balanced. A steady rhythm also supports your less visible systems (like digestion, hormones, and immunity), which helps your body stay resilient.

When your circadian rhythm is disrupted, you may notice it in subtle ways like grogginess in the morning, restlessness at night, or an afternoon slump that feels hard to shake. Over time, chronic disruption from stress, night shifts, or irregular sleep patterns can strain your health, raising the risk of issues like blood sugar imbalance, heart problems, or mood disorders.

The upside, though, is that your internal clock is adaptable. So simple daily cues, like light and steady sleep hours, can bring it back into balance.

How does circadian rhythm work in sleep-wake cycles?

Your circadian rhythm is regulated by signals that tell your body when to wake and when to rest, with light being the strongest cue. When sunlight enters your eyes in the morning, it activates a part of the brain called the suprachiasmatic nucleus (SCN). The SCN sets off a chain reaction, where your cortisol levels rise, helping you feel alert, while your body temperature increases to boost energy.

As daylight fades, your brain flips the switch. Darkness triggers the release of melatonin, which helps you feel sleepy, while your body temperature drops slightly to prepare for rest. This daily rhythm keeps you alert in the morning and naturally drowsy at night.

But when light cues or routines are off—like if you scroll on your phone late at night or miss getting in some sunlight during the day—the signals can get scrambled. This, in turn, leads to inconsistent sleep, sluggish energy, and an out-of-sync body clock.

10 ways to support your circadian rhythm for better sleep

While your circadian rhythm may get off track quickly, the good news is that it can bounce back just as fast. Instead of thinking that you need to overhaul your whole life, focus on small, consistent habits.

Following them for a few weeks can send strong signals to your body and brain about when it’s time to wake up, stay alert, and rest. Here are 10 practical ways to support your internal clock.

1. Get natural light first thing in the morning

Light is the strongest signal for your circadian rhythm. Try to step outside within the first hour of waking: even 10–15 minutes of sunlight can help set your body clock for the day.

If you work early shifts or live somewhere with long winters, a light therapy lamp can be a helpful backup. Also, make sure to open your curtains when you’re up. It helps signal to your circadian rhythm that it’s time to start the day.

2. Keep a steady sleep schedule

Your brain thrives on consistency. Going to bed and waking up at roughly the same time (yes, even on weekends) helps your internal clock stay aligned.

If you need to adjust your bedtime to make sure that weekdays and weekends stay consistent, shift it gradually by 15–30 minutes every few days, rather than making big jumps. Your body will slowly get used to it, and you’ll start feeling drowsy when it’s time to go to bed.

💙 Try a soothing Sleep Story like Dream With Me with Harry Styles to help you drift off faster.

3. Create a gentle bedtime routine

Cues that signal it’s time to wind down can work wonders on your circadian rhythm, so creating a bedtime routine is ideal. Try a short ritual like reading a book, stretching, journaling, or making herbal tea.

Even dimming the lights 30 minutes before bed helps your body prepare for sleep. You can mix and match among different options to find the bedtime routine that works best for you.

4. Limit evening light exposure

Bright lights at night (especially from phones, tablets, or TVs) can trick your brain into thinking it’s still daytime. Try using a blue-light filter, switching to warm lighting at home, or setting a tech curfew an hour before bed.

Being on your phone or computer too late at night can also keep your brain in go mode, as opposed to calming it down for sleep.

5. Move your body during the day

Physical activity, whether it’s a brisk walk, yoga, or a gym session, can help strengthen your circadian rhythm by increasing body temperature and signalling to your body it’s time to be awake. The key, though, is in the timing.

Aim to be active during daylight hours, as exercise too close to bedtime can leave you feeling wired instead of relaxed.

💙 Learn to look forward to exercising with this Moving for Fun session with Mel Mah.

6. Time your meals with care

Your digestive system has its own mini clock that links up with your circadian rhythm, so eating at regular times helps reinforce your body’s schedule.

Try to keep meals consistent from day to day and avoid heavy, late-night dinners that can interfere with sleep. After all, when your digestive system is working overtime, it could prevent your body from relaxing into sleep.

7. Create a sleep-friendly environment

Your bedroom should feel like a cue for rest. Keep it cool, dark, and quiet: think blackout curtains, white noise machines, or even a fan.

Small touches—like keeping your phone outside the bedroom or using a bedside lamp instead of overhead lighting—can also make a big difference.

8. Time your caffeine intake

Caffeine lingers in your system for hours. While you might look forward to your late-afternoon coffee for a break, it can delay melatonin release and push your sleep cycle later.

If you struggle with falling asleep, try cutting off caffeine after lunch. If you still need the mid-day ritual, there are plenty of non-caffeinated drinks available.

9. Manage stress before bed

Stress hormones, such as cortisol, compete with melatonin, which can make it harder to wind down before bed. The best way to combat this is by establishing calming habits at night.

Activities like deep breathing, journaling, or taking a warm shower can all help your body shift into a more relaxed state. If you can’t dedicate a ton of time to it, that’s okay too. Even five minutes of a soothing activity can be enough.

💙 Ground your body and stress less with this Pump the Brakes on Stress meditation with Jay Shetty.

10. Use travel and shift-work strategies wisely

If you frequently travel across time zones for work or pleasure, try adjusting your light exposure and meal times gradually to ease the transition before you leave and when you arrive.

For shift work, the best way to deal with a lack of light is to create artificial “daylight” with lamps during your work hours, and block out the daylight with blackout curtains or sleep masks when it’s time to rest.

What is circadian rhythm FAQs

What is the definition of circadian rhythm?

Circadian rhythm is your body’s natural 24-hour clock. It helps regulate sleep, energy, hormones, digestion, and mood by working in the background every day, using signals like light, darkness, and activity to keep your body on a regular cycle.

The rhythm is actually controlled by a tiny part of your brain called the suprachiasmatic nucleus, which acts like the main center of your body’s internal clock.

What are the benefits of the circadian rhythm?

When your circadian rhythm is in sync, your body works more efficiently. Sleep tends to feel deeper and more refreshing, your energy is steadier, and your ability to focus improves.

It also supports key systems like hormone balance, immune function, and metabolism. A steady rhythm helps regulate appetite hormones, allowing you to feel hungry and full at the right times, and your cells to repair overnight.

In short, a healthy circadian rhythm makes it easier for your body and mind to stay balanced.

What happens if your circadian rhythm is disrupted?

Short-term disruption of your circadian rhythm might show up as grogginess in the morning, difficulty falling asleep at night, or energy crashes during the day.

Long-term disruptions, which can occur due to issues like chronic stress, shift work, or irregular sleep schedules, can strain your health in more subtle ways. Research has linked ongoing circadian misalignment to lowered immunity, blood sugar imbalances, heart problems, and mood disorders.

This doesn’t mean one late night will cause lasting harm, but it does highlight why supporting your body’s clock is so important.

Can you reset your circadian rhythm?

Yes, you can absolutely reset your circadian rhythm — though it takes consistency. The most powerful ways to shift it include light exposure, meal timing, and sleep scheduling.

Here are a few key examples that can help reset your circadian rhythm:

Get morning sunlight soon after waking to anchor your rhythm.
Go to bed and wake up at regular times, shifting gradually over a period of days if you need to adjust.
Keep meals consistent, avoiding heavy or late-night eating.

Small, steady changes over time are key to helping your brain and body realign with a healthier rhythm.

How long does it take to fix circadian rhythm issues?

It depends on the seriousness of your situation, but many people start noticing improvements in their circadian rhythm within a week or two of consistent changes. If you’re adjusting for jet lag, it often takes about one day per time zone crossed.

For larger disruptions, like shift work or long-term irregular schedules, it may take several weeks of steady light exposure, consistent sleep times, and daily cues for your body to fully adapt. The key is patience and consistency. Your body responds best when you give it clear signals day after day.

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Calm Editorial Team