Cortisol

Cortisol is produced by the adrenal glands under instruction from the pituitary. It follows a strong daily rhythm: highest within an hour of waking, falling through the day, lowest around midnight. That rhythm is the reason sampling time matters so much for interpreting the number.

Its job is to mobilise energy. It raises blood glucose, releases fatty acids, and shifts the body toward using fuel rather than storing it. It also modulates immune activity and helps regulate blood pressure. The daily peak is what gets you out of bed.

Below 140 nmol/L on a morning sample is under the reference range. Reported effects include difficulty waking, fatigue that does not improve with rest, low blood pressure, salt craving and poor tolerance of physical or emotional stress.

Sampling time is the first thing to rule out. A sample drawn late in the morning or in the afternoon will read lower simply because of the rhythm, without indicating anything about output.

Long-term use of corticosteroid medication, including inhaled and topical forms, suppresses adrenal output. A genuinely low morning result is worth discussing with your practitioner rather than interpreting alone.

Between 140 and 620 nmol/L your morning cortisol sits inside the reference range for this panel.

A single measurement captures one point on a curve. The shape of the rhythm across the day carries information that one number cannot, which is why persistent symptoms alongside an in-range result are still worth raising.

Above 620 nmol/L on a morning sample is above the reference range. Sustained elevation is associated with disturbed sleep, central weight gain, raised blood glucose, reduced recovery from training and lower stress tolerance.

Acute causes are common and often overlooked: an early start, a stressful commute, a fasted training session or simple anxiety about the blood draw itself will all raise the reading.

Sustained elevation without an obvious situational cause is a reason to speak to your practitioner.

The Western pattern keeps the stress response switched on far longer than the system was built for. Chronic work pressure, artificial light after dark, short sleep and stimulant intake through the afternoon all act on the same axis.

Light is the underrated one. Evening screen exposure delays the fall in cortisol and shifts the whole rhythm later, which then flattens the morning peak the next day. This marker sits at the centre of the Stress Adaptation domain of the Western Lifestyle Index.

Steady blood glucose reduces cortisol excursions. Protein and fibre with each meal do more for this than any specific food.

Caffeine raises cortisol and has a half-life of five to six hours, so an afternoon coffee is still active at bedtime. Moving the last cup earlier is one of the more effective single changes.

Alcohol disrupts the second half of the night and raises next-morning cortisol, even when it shortens the time taken to fall asleep.

Magnesium glycinate supports sleep quality and is often depleted where stress is chronic, so it is worth addressing the magnesium result first.

Ashwagandha and rhodiola are the adaptogens most commonly used where the pattern is sustained elevation. Effects vary between individuals.

Phosphatidylserine is used for evening elevation specifically. Discuss any of these with your practitioner if you take medication, since interactions are possible.