Circadian Rhythm: Your Body's Internal Clock Explained

Your body runs on an internal 24-hour clock that affects nearly every aspect of your health. Understanding your circadian rhythm is key to optimizing sleep, energy, and overall well-being.

What Is the Circadian Rhythm?

The circadian rhythm is a 24-hour internal clock that regulates your sleep-wake cycle and many other bodily functions. "Circadian" comes from Latin meaning "about a day." This biological clock is controlled by a region of your brain called the suprachiasmatic nucleus (SCN), located in the hypothalamus.

Your circadian rhythm doesn't just control sleep—it influences hormone release, body temperature, digestion, immune function, and even cognitive performance throughout the day.

How It Works: The Light Connection

Light is the primary signal (called a "zeitgeber") that synchronizes your internal clock with the external world. Here's the process:

1. Light enters your eyes and is detected by special photoreceptors
2. These signals travel to the SCN in your brain
3. The SCN coordinates with the pineal gland
4. The pineal gland regulates melatonin production—the "sleep hormone"

Morning light suppresses melatonin and signals wakefulness. Darkness triggers melatonin release, preparing you for sleep.

Your 24-Hour Cycle

A typical circadian rhythm follows this pattern:

• 6-8 AM: Cortisol rises, melatonin drops, body temperature increases
• 9-11 AM: Peak alertness and concentration
• 2-3 PM: Post-lunch dip in alertness (natural—not just from food)
• 4-6 PM: Peak physical performance and coordination
• 7-9 PM: Melatonin begins rising, body temp starts dropping
• 10 PM-2 AM: Deepest sleep occurs
• 3-6 AM: Body temperature at lowest, most REM sleep

Use our Circadian Rhythm Planner to map your personal rhythm.

Chronotypes: Morning Larks vs Night Owls

Not everyone's circadian rhythm is identical. Your "chronotype" is your natural preference for sleep timing:

• Morning types (larks): Peak earlier, prefer 6 AM wake times
• Evening types (owls): Peak later, prefer staying up past midnight
• Intermediate: Most people fall somewhere in between

Chronotype is largely genetic—about 50% heritable. Fighting your natural chronotype leads to "social jet lag" and reduced well-being.

What Disrupts Your Circadian Rhythm?

• Artificial light at night: Especially blue light from screens
• Irregular sleep schedule: Different bed/wake times
• Shift work: Working against natural light-dark cycles
• Jet lag: Crossing time zones faster than your clock can adjust
• Lack of morning light: Staying indoors reduces clock-setting signals

How to Optimize Your Circadian Rhythm

1. Get Bright Light in the Morning

Expose yourself to bright light within 30-60 minutes of waking. Sunlight is best (10,000+ lux), but a light therapy lamp works too. This anchors your circadian rhythm.

2. Dim Lights in the Evening

Starting 2-3 hours before bed, dim overhead lights and avoid bright screens. Use night mode on devices and consider blue-light blocking glasses.

3. Keep a Consistent Schedule

Go to bed and wake up at the same time every day—including weekends. Consistency is one of the most powerful tools for circadian health.

4. Time Your Meals

Eating signals your peripheral clocks. Avoid large meals within 3 hours of bedtime. Some research suggests time-restricted eating (e.g., 10-hour window) supports circadian alignment.