Circadian Rhythm
Your body's master clock. The circadian rhythm is a 24-hour cycle controlling sleep, hormone release, metabolism, cellular repair, and immune function. Every cell has its own clock, synchronized by light and meal timing. Disruption is linked to obesity, diabetes, cancer, and mental illness.
The Daily Rhythm
Morning (6-10am)
Cortisol peaks. Melatonin drops. Blood pressure rises. Alertness increases. Best time for light exposure.
Midday (10am-2pm)
Peak alertness. Best coordination. Highest reaction time. Cognitive performance peak.
Afternoon (2-6pm)
Best cardiovascular performance. Highest muscle strength. Body temperature peaks.
Night (10pm-6am)
Melatonin rises. Growth hormone peaks. Cellular repair. Memory consolidation. Temperature drops.
Zeitgebers (Time-Givers)
Light Exposure
Most powerful. Morning bright light sets clock. Evening blue light disrupts. Eyes send signal to SCN.
Meal Timing
Peripheral clocks sync to food. Eating at night disrupts rhythm. Time-restricted eating helps.
Exercise
Morning exercise strengthens rhythm. Late exercise can delay sleep. Consistency matters.
Social Interaction
Human contact influences rhythm. Schedules, routines. Isolation disrupts.
Temperature
Body temp fluctuates 24h. Cool environment promotes sleep. Sauna/cold exposure timing.
Sleep Schedule
Consistent bed/wake times. Even on weekends. Social jet lag harms health.
Consequences of Disruption
Metabolic Disease
Shift work increases diabetes risk 40%. Obesity link. Insulin resistance. Meal timing matters.
Cancer Risk
Night shift = WHO carcinogen. Melatonin suppression. DNA repair impaired. Breast cancer link.
Mental Health
Depression, bipolar, anxiety. Sleep-wake disruption. Light therapy helps. Rhythm restoration.
Cardiovascular
Blood pressure dysregulation. Heart attack timing. Shift work increases risk.
Immune Function
Immune cells are rhythmic. Disruption = poor defense. Vaccine timing matters. Inflammation increases.
Cognitive Decline
Memory consolidation during sleep. Alzheimer's risk. Glymphatic cleaning at night.
Optimizing Circadian Health
Morning Light
Get bright light within 30-60 min of waking. 10+ minutes outside. Light box if needed.
Evening Dim
Dim lights 2-3 hours before bed. Blue-blocking glasses. Red/amber lighting.
Consistent Schedule
Same sleep/wake daily. Weekend consistency. Avoid "social jet lag."
Time-Restricted Eating
Eat during daylight hours. 10-12 hour window. No late-night eating. Breakfast matters.
Exercise Timing
Morning or early afternoon best. Avoid vigorous exercise 3h before bed. Consistency key.
Cool Sleeping Environment
65-68°F optimal. Body temp must drop. Hot shower before bed (then cool).