Sleep, stress and exhaustion
Recovery happens at night. If cortisol does not fall in the evening, melatonin does not rise and deep sleep stays short — and the next day the very reserve that should absorb strain is missing.
So what comes first is not a single value but the course of the day: several saliva samples show whether the curve still has the right shape.
What is measured here
Speichel
Speichel
Urin
Urin
Urine, blood
Urin
Urin
Kapillarblut
several sample typesNot the level, but the shape of the curve
A single cortisol value tells you almost nothing, because it changes several times over across the day. Several samples show the course: the rise after waking, the fall through the day and the low point at night.
Schematic curves, not measured ones. We do not use the terms “adrenal weakness” or “adrenal fatigue” — they are not an established diagnosis. What a profile means is for a practitioner to interpret.
From tryptophan to sleep — four steps, four conditions
Melatonin does not appear out of nowhere. It is formed from tryptophan via serotonin, and each conversion step needs particular cofactors. If one is missing, sleep is what is missing at the end of the chain.
A description of a metabolic pathway. All the substances named are cofactors of these steps — that is not a statement that supplementing them improves sleep.
Each arrow stands for a conversion step with its own cofactor needs. The chain does not break when something is missing — it runs more slowly.
Strain on one side, protection on the other
Every time energy is produced, reactive oxygen species arise. As long as the protective side keeps up, this is normal and even necessary — it is part of how the body adapts. When the load exceeds capacity for a long time, this is called oxidative stress.
Antioxidants in high doses are not automatically a good thing: in training studies, high doses of vitamins C and E weakened the adaptation to training. That is why we measure before supplementing.
The research is not consistent
Studies with night-time cortisol measurement and sleep EEG found less deep sleep when night values were raised. Experimental doses of cortisol, by contrast, led in other studies to more deep sleep and less REM sleep in the short term. What is established is the link between lack of sleep and raised evening cortisol, not every direction of the effect.
The rating describes how well supported the statement is — it is not itself measured.
A list of sources that drops the inconvenient study is not a list of sources. The study with the opposite result is therefore in the sources below, with its name and year.
Deep sleep needs cortisol at its lowest
Deep sleep falls in the first half of the night — exactly when cortisol is at its lowest. This is the phase in which tissue repair takes place, growth hormone is released and the brain is cleared out. If cortisol stays high in the evening, sleep shifts into the lighter stages.
A schematic course based on the literature on circadian rhythm, not a curve from measurements. The curves show the direction, not absolute values.
Where the figures come from
- Sleep and Circadian Regulation of Cortisol: A Short Review, PMC 2022.
- Reduced slow-wave sleep and altered diurnal cortisol rhythms in patients with Addison’s disease, European Journal of Endocrinology 2018.
- Daily associations between salivary cortisol and electroencephalographic-assessed sleep: a 15-day intensive longitudinal study, SLEEP 2024.
- Balbo M, Leproult R, Van Cauter E, Impact of sleep and its disturbances on hypothalamo-pituitary-adrenal axis activity, University of Chicago.
- Acute Cortisol Administration Promotes Sleep Intensity in Man, Neuropsychopharmacology 2003 — the study with the opposite result.
- Review articles on redox signalling, antioxidants and training adaptation.
Why four samples instead of one?
Cortisol changes several times over across the day. A single value can look high because it was taken in the morning, or low because it was taken in the evening — neither tells you anything.
Only the shape of the curve shows whether the rise after waking is there and whether the fall across the day happens.
Is a flat profile a diagnosis?
No. A flat curve is a reason to look further, not a finding. It can have many causes, from shift work through illness to the sample collection itself.
We do not use the terms “adrenal weakness” and “adrenal fatigue”. They are not an established diagnosis.
What has sleep got to do with cortisol?
The link runs both ways. Raised cortisol in the evening shortens deep sleep, and too little sleep raises evening cortisol the next day.
Out of that loop comes what many describe as “tired and wired at the same time”. The evidence is not consistent in every direction — that is set out in the section above.
Should I take antioxidants?
Not without measuring first. In several training studies, high-dose vitamins C and E weakened the body's adaptation to training — more is not better here.
Reactive compounds have a job to do: in moderate amounts they are involved in steering how the body adapts. The problem only starts when they lastingly outweigh the protective side.
When does this belong in a medical practice?
With lasting exhaustion, always. Physical conditions can lie behind it — thyroid, blood count, heart, depression — that a saliva sample does not show.
These analyses supply measured values with the laboratory's reference range. A diagnosis is made by a doctor or a non-medical practitioner.
Everything on this page comes from study results and describes groups, not individual cases. Persistent exhaustion needs to be assessed by a doctor.