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The morning peak
People wake because cortisol rises, a process called the cortisol awakening response. It can be matched to outside cues, which is why some people wake a minute before the alarm. The higher the peak in the first sixty minutes, the better mood, focus, attention, and learning are for the day.
What a flat curve does
The peak also sets the baseline for everything after it. With a high morning peak, a stressful text produces a brief blip that returns to normal. With a flattened curve, the same text produces a bigger, longer spike riding on a higher baseline, and cortisol's interaction with melatonin disrupts sleep. A flat curve goes along with shorter lifespan and less recovery from every kind of illness.
Mapping the curve
The curve was mapped with repeated blood draws around the clock and then tracked against caffeine, cold plunges, exercise, and sunlight. Cushing syndrome, a massive overproduction of cortisol, is very rare. Most people's morning cortisol is too low and their afternoon and nighttime cortisol is too high.
How big is the morning cortisol jump?
Saliva studies, including a 1997 study by Jens Pruessner's group, found that cortisol climbs sharply within thirty minutes of waking and then declines through the day. The rise is often 50 percent or more above the level at waking. It happens even when people wake without an alarm. The pattern is among the most reliable features of the stress hormone system.
Why does cortisol come in pulses?
Stafford Lightman's lab at the University of Bristol sampled blood from rats and people at frequent intervals and found that cortisol is released in pulses roughly every hour. The pulses are tallest in the early morning and shrink toward midnight. The daily rhythm is built from many smaller bursts, not a smooth curve. Frequent sampling is what made the pulses visible.
Why is Cushing syndrome so rare?
Surgeon Harvey Cushing described the condition in 1932, in patients whose pituitary tumors caused their adrenal glands to overproduce cortisol. Estimates put new diagnoses at roughly two to eight per million people per year. Symptoms include weight gain in the face and trunk, thin skin, and high blood pressure. Most cases in adults involve a small tumor or a glucocorticoid medication.
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