Pillars
Chronobiology.
Every hormone, immune function, and metabolic process runs on a circadian schedule. The disruption is measurable, and the consequences are systemic.
Why it matters
Your body runs on a clock. Cortisol, melatonin, growth hormone, insulin sensitivity, gut motility, immune function, and DNA repair all peak and trough on a 24-hour rhythm. Disrupt the clock and you disrupt all of it. Most chronic disease shows a circadian signature long before it shows a diagnosis.
What it is
Chronobiology is the study of biological time. A master clock in the brain (the suprachiasmatic nucleus) reads light through your eyes and synchronizes thousands of peripheral clocks in every tissue. Food timing, movement, and stress all carry timing signals too. When those signals contradict each other, the system desynchronizes.
What I read for
Morning cortisol and the diurnal curve. Sleep architecture, when wearable data is available. Patterns in fasting glucose and insulin that suggest timing problems rather than absolute dysregulation. The melatonin pattern, when it is worth measuring. The behaviors that are setting or breaking the clock.
Signs it isn't working
What this shows up as.
Most cases touch more than one of these. Recognize what you feel.
- Poor sleep quality, frequent middle-of-the-night waking, or a tired-and-wired pattern.
- Energy crashes at consistent times of day.
- Mood shifts that track with light, season, or shift work.
- Weight that resists effort, especially central weight gain.
- Daytime fatigue that does not match the hours you spent in bed.
Levers
Things you can do.
Practical, ordered roughly by impact. The plan that fits you depends on what your biology shows.
01
Morning sunlight, 10 to 15 minutes
Within 60 minutes of waking, outdoors, eyes open. The single strongest zeitgeber available.
02
Consistent sleep and wake times
Same window seven days a week. Your clock cannot read inconsistent inputs.
03
Evening light hygiene
Dim and warm in the last 90 minutes before bed. Bright overhead light at night is the modern equivalent of a stimulant.
04
Time-restricted eating
A 10 to 12 hour eating window, with the largest meal earlier in the day.
05
Exercise timing
Morning or early afternoon for most people. Late-evening high-intensity work disrupts sleep more than it builds fitness.
Written by
Daniel Tagge, MD
Board-certified family physician. North Carolina’s only physician certified in Health Optimization Medicine. Third-generation physician. NPI 1225562218.
About Dr. TaggeWhere this shows up
Symptoms this system drives.
When this system is off, here is what patients usually feel. Open any symptom for the full read.
Work with me
This area inside the Partnership.
The panels that read this system run as part of a Precision Partnership membership. I interpret your data into a written Plan that traces every recommendation back to a finding.
Connected systems
Read alongside.
No system stands alone. These are the areas that interact most with this one.
From the library
On this system.
Long-form writing on the system above, from my own clinical lens.
Questions
About Chronobiology.
Do you measure circadian rhythm directly?
I read its signatures across other panels. Morning cortisol, the diurnal curve, fasting glucose patterns, and wearable sleep data give me enough to act on. Direct dim-light melatonin onset testing exists but is rarely necessary clinically.
What about shift workers?
Shift work is one of the highest-cost circadian disruptions known. I work with shift workers, but the plan focuses on protecting what circadian function we can rather than pretending the schedule is not happening.
Is melatonin supplementation safe?
Used correctly, yes. Most people use it at the wrong time and at doses that are an order of magnitude too high. When I prescribe melatonin, it is small, early-evening, and time-bounded.