Understanding Your Body's Circadian Rhythm

Are you a night owl or a morning person? Your answer has more to do with biology than habit. Your circadian rhythm, which is your body’s internal 24-hour clock, controls nearly every system in your body, from energy and focus to digestion and immune function.

New research shows that keeping your circadian rhythm in sync matters far beyond getting a good night’s sleep. A 2024 scientific report from the American Heart Association links circadian disruption to higher rates of heart disease, type 2 diabetes, obesity and high blood pressure.

The good news: You can guide your biological clock back on track with a few consistent habits.

Key Takeaways: Your Circadian Rhythm

• Your circadian rhythm controls more than sleep.
• Light is the most powerful signal for your biological clock.
• Consistent habits can reset a disrupted clock.

What Is A Circadian Rhythm?

Your circadian rhythm is your body’s internal 24-hour clock. It runs in the background every day. It coordinates when you sleep, when you digest food, when your hormones release and when your cells repair themselves.

Like a conductor, one small region in your brain keeps everything in your body running on the same schedule. When that schedule is disrupted, it can hurt your health.

How Your Biological Clock Works

Light. Light is the most powerful signal for your body clock. Morning sunlight tells your brain it’s time to wake up and start your day. As evening sets in, fading light tells your brain to wind down and prepare for sleep.

Melatonin. As the light fades, your brain releases melatonin, the hormone that makes you feel sleepy. It rises naturally each evening, peaks in the middle of the night and fades again by morning. It also supports your immune system and heart health, not just your sleep.

What Your Circadian Rhythm Controls

Your biological clock does more than manage your sleep. Your body follows a consistent schedule every day.

What Happens When Your Circadian Rhythm Is Disrupted?

Life doesn’t always cooperate with your body clock. A one-time disruption, like jet lag after a trip, is uncomfortable, but your body recovers. The concern is when any disruption becomes the norm.

Common causes of circadian disruption

• Chronic stress
• Excessive screen time at night
• Jet lag
• Nighttime eating
• Shift work and irregular schedules
• Social jet lag

Health conditions linked to circadian disruption

Research links chronic circadian disruption to:

• Sleep disorders: Insomnia, sleep apnea and restless legs syndrome are all tied to a disrupted body clock.
• Weight gain and diabetes: When your clock is off, your body struggles to regulate appetite and blood sugar.
• Heart disease and high blood pressure: A 2024 American Heart Association report found that disrupting your body clock raises your risk of heart disease and high blood pressure.
• Depression and mood changes: A 2024 study tracking over 800 medical residents found that circadian disruption was linked to lower mood and higher depression scores.
• Seasonal depression (SAD): Less daylight in fall and winter can throw off the hormones that regulate your mood.
• A weaker immune system: Your immune system runs on a schedule, too. Disrupt it and you may get sick more easily or respond less well to vaccines.

Can Your Circadian Rhythm Change Over Time?

Yes, your circadian rhythm can change, and this matters. Your biological clock is not fixed for life. It changes naturally across your life and adapts in response to changes.

Adolescents and young adults tend to have a "delayed" chronotype, which means their clock runs later. This explains why teenagers stay up late and struggle to wake early. As adults age, the clock shifts earlier, which is why many older adults feel tired in the evening and rise at dawn.

Your genes play a role in whether you’re a morning person or a night owl, but your daily habits can shift that over time.

Six Ways To Support Your Body Clock

Small, consistent habits make a big difference. Here’s where to start:

1. Wake up at the same time every day. Yes, even on weekends. Your body clock thrives on routine.
2. Get outside in the morning. Even 10 minutes of natural light helps your brain wake up and sets your clock for the day.
3. Dim the lights before bed. Turn off screens an hour before sleep and keep your bedroom cool, dark and quiet.
4. Eat during daylight hours. Your digestive system follows a clock, too. Try not to eat within two to three hours of bedtime.
5. Exercise consistently. Morning or early afternoon exercise works best for most people’s sleep. If you prefer evenings, try to finish by 7pm.
6. Wind down before bed. A few minutes of calm breathing or light stretching can lower stress hormones and help your body shift into sleep mode.

Circadian Health For Shift Workers

Shift work is hard on your body clock. If your schedule changes often or you work nights, these tips can help:

• Ask your doctor about melatonin to help reset your clock between shifts.
• Get regular checkups — shift workers have a higher risk for heart disease and metabolic conditions.
• Keep your sleep schedule as consistent as you can, even on days off.
• Use blackout curtains to protect your daytime sleep.

When To See A Doctor About Poor Sleep

Many people assume poor sleep is just part of life. Sleep disorders are medical conditions that respond well to treatment. Consider talking with your doctor if you:

• Have trouble falling or staying asleep most nights
• Wake up tired even after a full night’s sleep
• Snore loudly
• Can’t stay awake during the day
• Feel uncomfortable, or have restless legs at night
• Notice your mood, focus or energy gets worse
• Feel down or low-energy every fall and winter

Ready to sleep better? The Franciscan Health Sleep Medicine team offers comprehensive evaluations, including sleep studies, to help you find the answers — and the rest you deserve. Find a Franciscan Health sleep specialist near you.