Cortisol rhythm
Cortisol shows the strongest diurnal pattern:
- Lowest around midnight
- Begins rising 2-3 hours before waking
- Peaks 30-45 minutes after waking (cortisol awakening response, CAR)
- Declines through the day
- Lowest in evening
The CAR is essential for normal energy, mood, and metabolic readiness for the day.
Testosterone rhythm
In men:
- T pulses during sleep, particularly REM
- Peaks at waking (~7-9 AM)
- Declines through the day
- Lowest in evening
- Lab draws should be 8-10 AM for accurate measurement
Growth hormone rhythm
GH is highly pulsatile:
- 4-5 pulses per night, mostly during slow-wave (deep) sleep
- Peak release in first half of sleep
- Some daytime pulses but smaller
- Total daily GH largely depends on deep sleep quality
Sleep deprivation crashes GH output.
Melatonin and circadian
Melatonin from pineal gland:
- Begins rising 2 hours before habitual sleep onset
- Peaks during sleep
- Falls with dawn light exposure
- Light exposure (especially blue) suppresses melatonin
Melatonin is the master circadian signaling molecule.
Thyroid rhythm
TSH shows modest diurnal variation:
- Peaks late evening / early morning hours
- Lower in afternoon
- Daily variation within ~30%
- Lab draws should be consistent timing for tracking
Insulin sensitivity rhythm
Insulin sensitivity follows diurnal pattern:
- Best in morning
- Deteriorates through the day
- Lowest at night
- This is part of why late eating tends to drive worse glycemic outcomes
What disrupts rhythms
- Shift work
- Jet lag
- Late-night light exposure (phones, screens)
- Inconsistent sleep timing
- Late eating
- Late caffeine
- Late alcohol
- Chronic stress
Optimization strategies
- Consistent sleep-wake timing (most powerful single intervention)
- Morning sunlight exposure (anchors circadian)
- Limit late blue light
- Earlier eating window
- Limit late caffeine and alcohol
- Adequate sleep duration (7+ hours)
- Cool, dark sleeping environment
The clinical insight: Diurnal rhythm consistency is one of the most underutilized hormonal interventions. Many patients seeking hormonal optimization can move major markers (cortisol, T, GH) substantially through sleep timing alone, before any medication consideration.
Bottom line
Major hormones follow strong diurnal patterns tied to sleep-wake cycles. Disrupting rhythms through shift work, late-night activity, or inconsistent sleep dysregulates hormone biology system-wide. Optimizing rhythm through consistent sleep timing, morning sun, and reduced evening disruptors supports hormone health.