Circadian Rhythm Simulator

\uD83E\uDD14 What Is a Circadian Rhythm?

Your body runs on a 24-hour internal clock driven by the suprachiasmatic nucleus (SCN) in the brain. This master clock synchronizes every cell's timing with light-dark cycles, controlling when melatonin rises (signaling sleep), when cortisol surges (waking you up), and how body temperature fluctuates throughout the day.

Why does this matter? Disrupted circadian rhythms are linked to obesity, diabetes, depression, cancer, and cardiovascular disease. Understanding your body clock lets you optimize sleep, alertness, and overall health by aligning behavior with biology.

📖 Deep Dive

Analogy 1

Think of the SCN as a conductor leading an orchestra. Each organ is a musician with its own instrument and rhythm. The conductor (SCN) uses light as the baton to keep everyone in sync. When you fly across time zones, it is like the conductor suddenly starts waving the baton at a different tempo — the musicians stumble and need days to find the new beat. That re-synchronization struggle is jet lag.

Analogy 2

Melatonin and cortisol work like opposing traffic signals. When melatonin turns green (rises at night), it signals the body to slow down and sleep. When cortisol turns green (surges at dawn), it tells the body to wake up and go. Staring at a phone screen at midnight is like someone flashing a bright spotlight at the melatonin signal — it confuses the entire intersection, delaying the green light and causing a hormonal traffic jam.

🎯 Simulator Tips

Beginner

Press Start and watch the clock hand sweep through 24 hours — observe how melatonin (blue) and cortisol (orange) curves mirror each other.

Intermediate

Click the Jet Lag button and observe the SCN pulse frequency drop as the body struggles to re-entrain to the shifted schedule.

Expert

Set Wake Time to 5 AM (lark schedule) and compare alertness at 2 PM vs the default 7 AM wake — earlier risers hit the afternoon dip sooner.

📚 Glossary

Circadian Rhythm

~24-hour biological clock governing sleep-wake cycles, hormone release, and metabolism in all organisms.

SCN

Suprachiasmatic Nucleus — master clock in the hypothalamus synchronizing circadian rhythms to light-dark cycles.

Melatonin

Hormone produced by the pineal gland in darkness, signaling sleep time. Suppressed by blue light.

Cortisol

Steroid hormone peaking at dawn (cortisol awakening response), promoting alertness, metabolism, and immune readiness.

Chronotype

Individual preference for sleep-wake timing: morning larks, night owls, or intermediate types.

Zeitgeber

Environmental cue that synchronizes the biological clock, primarily light but also food and temperature.

DLMO

Dim Light Melatonin Onset — the time in the evening when melatonin begins to rise, marking circadian evening.

Clock Genes

Genes (CLOCK, BMAL1, PER, CRY) forming molecular feedback loops driving circadian oscillations.

Jet Lag

Misalignment between internal clock and external time zone after rapid travel across time zones.

Shift Work Disorder

Chronic circadian disruption from rotating or night shifts, increasing risk of metabolic and cardiovascular disease.

Chronotherapy

Timing medication administration to circadian rhythms for maximum efficacy and minimum side effects.

Light Therapy

Using bright light exposure at specific times to shift circadian phase, treating SAD and sleep disorders.

🏆 Key Figures

Jeffrey Hall, Michael Rosbash, Michael Young (1984)

Discovered molecular mechanisms controlling circadian rhythm (period gene), Nobel Prize in Physiology 2017

Satchin Panda (2012)

Salk Institute researcher who discovered time-restricted eating's metabolic benefits and light-sensing melanopsin

Russell Foster (1991)

Oxford professor who discovered non-visual light receptors (melanopsin) in the eye regulating circadian rhythms

Till Roenneberg (2003)

LMU Munich chronobiologist who developed the Munich Chronotype Questionnaire mapping human chronotypes

Colin Pittendrigh (1954)

'Father of circadian biology' who established core properties of biological clocks

🎓 Learning Resources

Molecular components of the circadian clock in Drosophila [paper]
Foundational work on period gene and circadian molecular feedback loops (Nobel Prize 2017)
Time-Restricted Feeding and Its Effects on Obesity [paper]
Satchin Panda's study showing meal timing affects metabolism independently of calories (Cell Metabolism, 2012)
Society for Research on Biological Rhythms [article]
Scientific society advancing circadian rhythm research
Circadian Clock Tool [article]
Satchin Panda's app for tracking personal circadian patterns

💬 Message to Learners

Your body is a precision timepiece billions of years in the making. Every hormone surge, every temperature shift follows a script written by evolution. This simulator lets you see that invisible script — and learn how light, food, and habits can rewrite it for better or worse.