Cortisol and sleep: what studies show and what they don't

Cortisol and sleep are tied together by the body clock. Cortisol rises toward morning and is lowest early in sleep. The questions people ask are whether poor sleep changes cortisol, and whether cortisol is why they can’t sleep.

The studies find links between the two, but they don’t agree on which way the link runs, or even on whether cortisol ends up higher or lower. This page sets out what was found and what a cortisol test can and can’t tell you about your sleep.

Cortisol AM and PM

A morning result and a later one, because cortisol changes through the day. Follow the times on your lab order.

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A cortisol result can't diagnose a sleep problem. It shows your level at the time of each draw. If you take a steroid medicine, ask your prescriber how it affects results.

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The daily rhythm

A 2025 review describes the usual pattern. Cortisol climbs during the later part of sleep and peaks within 30 to 45 minutes after waking. It then falls through the day and reaches its lowest point in the early part of sleep (Int J Mol Sci, 2025). NIDDK puts the same idea simply: cortisol production normally drops just after a person falls asleep.

Because of this, a cortisol value only means something next to the time it was taken. The ranges and times on this site assume a person who sleeps at night. See the body clock and cortisol for the pattern in more detail.

Does poor sleep change cortisol?

Three kinds of study point in different directions.

Years of short sleep. The Whitehall II study followed UK civil servants for about 10 years. Sleep was self-reported at three points, and saliva was collected six times across one ordinary day. The analysis included 3,125 people. People who repeatedly reported sleeping five hours or less had lower cortisol on waking and a flatter fall through the day than people who never reported short sleep. Chronic insomnia symptoms did not show that flatter fall. Some groups had a steeper rise after waking, but the pattern was inconsistent. It reached statistical significance for two reports of short sleep and not three. The authors say they can’t rule out other explanations, and cortisol was measured on a single day (Psychoneuroendocrinology, 2016).

One night without sleep. In a small 2022 experiment, 23 young adults stayed awake for 24 hours. Their morning salivary cortisol was lower afterward, and markers of inflammation (CRP and IL-6) were higher. The paper itself notes that human studies have found cortisol to rise after sleep loss in some cases and fall in others. It also notes that whether people kept to the instruction to avoid caffeine was not checked, and that each person’s morning peak was not accounted for (Front Behav Neurosci, 2022).

People with insomnia compared with people without. A 2026 meta-analysis pooled 32 studies of circulating biomarkers in insomnia. Ten reported hormone measures, and the pooled result for cortisol was higher in people with insomnia. But the studies differed so much from one another (an I-squared of 97.6 percent) that the authors say pooled numbers show a general trend, not a precise size. They rate the certainty of the evidence as low to very low. The studies were observational comparisons of groups, so they can’t show which came first (Front Immunol, 2026).

So the findings conflict: lower on waking, flatter across the day, lower after a night awake, and higher in insomnia. Differences in who was studied, how sleep was defined and when and how cortisol was measured all make direct comparison hard.

Does cortisol cause insomnia or poor sleep?

The sources show association, not cause. The 2026 meta-analysis suggests that a state of high arousal could keep cortisol up and disrupt sleep, but it calls for longer studies to sort out cause and effect. A 2021 review of hair cortisol, a measure of longer-term cortisol exposure, says sleep disorders have been associated with high cortisol in adults and children, and it calls for more studies. Its own examples show the mixed picture: one study found that 12-month-old infants who slept 10 hours or more a night had lower hair cortisol than those who slept less, while another found that sleep measures were generally not linked to hair cortisol in children aged 2 to 6 (Life, 2021).

MedlinePlus describes the more usual causes of insomnia. Most chronic insomnia is secondary, meaning it is a symptom or side effect of another problem, such as a medical condition, a medicine or another sleep disorder. Caffeine, tobacco and alcohol can also cause it. When insomnia has no other cause, long-lasting stress, emotional upset, travel and shift work can be factors. See coffee and cortisol and alcohol and cortisol.

What a cortisol test can and can’t tell you about sleep

A cortisol blood test is used to help diagnose or rule out conditions that cause too much or too little cortisol, such as Cushing syndrome and adrenal insufficiency. It is not used to diagnose insomnia. MedlinePlus says insomnia is diagnosed from a medical history, a sleep history and a physical exam, and sometimes a sleep study.

A result also depends on more than sleep. MedlinePlus lists stress, pregnancy, exercise, hot and cold temperatures and some medicines, such as birth control pills, as things that can change a result. A single morning level after a bad night can’t separate those causes, and it can’t tell you whether your sleep is the reason or the result.

A morning sample plus a later one shows how far your level falls during the day, which is the question people often have in mind. See AM and PM timing. If your sleep schedule is not an ordinary night schedule, ask the clinician who orders the test how to time it, and follow the timing on your lab order.

When to see a clinician

MedlinePlus describes chronic insomnia as lasting a month or longer. It says insomnia can cause daytime sleepiness, a lack of energy, anxiety, depression and irritability, trouble focusing, and drowsiness while driving. Book an appointment if sleep trouble has lasted, or if it affects your days.

Cortisol-related conditions are a much less common reason for poor sleep, so sleep trouble alone isn’t a reason to suspect one. Tell a clinician if you also have the signs of too much cortisol, such as easy bruising and wide purple stretch marks (high cortisol), or of too little, such as long-lasting fatigue, weight loss and loss of appetite (low cortisol).

If you take a steroid medicine, don’t stop or change it because of sleep trouble. Ask your prescriber.