Quick answer: Cortisol is the main stress hormone made by the adrenal glands. It follows a daily rhythm: highest in the morning and lowest at night. It helps regulate blood sugar, blood pressure, immunity and energy. Very high cortisol (Cushing’s) or very low cortisol (adrenal insufficiency) are medical conditions; more subtle rhythm changes can come with chronic stress and poor sleep.
Key takeaways
Cortisol is the main stress hormone from the adrenal glands and is normally highest in the morning and lowest at night.
It helps regulate blood sugar, blood pressure, immunity and energy.
Very high or very low cortisol signals medical conditions, while subtler rhythm changes often come with chronic stress and poor sleep.
What is Cortisol?
Cortisol is a steroid hormone released by the adrenal glands in response to signals from the brain. It follows a daily rhythm and rises with stress.
Why Cortisol matters
Cortisol matters for blood sugar regulation, blood pressure, and immune and inflammation control. It also shapes energy and alertness and your sleep-wake rhythm.
Understanding your result
Reference ranges vary by lab, age and sex. Your provider interprets your result against the lab’s range and your overall picture, rather than chasing a single number. Functional labs are optional. They can be helpful in more complex cases.
What low Cortisol can mean
Low cortisol can mean adrenal insufficiency (Addison’s disease), pituitary problems, or stopping steroid medications abruptly.
What high Cortisol can mean
High cortisol can reflect chronic stress and poor sleep, Cushing’s syndrome, steroid medications, or severe illness.
What affects Cortisol
Cortisol is affected by time of day, stress, sleep and caffeine, medications including steroids and birth control, and the test type (blood, saliva or urine).
Ways to support healthy levels
Morning light and a consistent sleep schedule help, along with regular meals with protein. Stress practices such as breathwork (see breathwork) and adaptogens with guidance (see adaptogens) can also support healthy levels.
What does the research show about cortisol?
The Whitehall II study collected six saliva samples across a normal weekday from 4,047 adults with an average age of 61 and followed them for about 6.1 years. A flatter fall in cortisol from morning to night was linked with a 30% higher risk of death per standard deviation (hazard ratio 1.30), driven mainly by heart-related deaths (hazard ratio 1.87), while a single morning value and the waking rise were not linked with death. Cortisol was sampled on only one day, and the participants were civil servants, so the results may not apply to everyone. (Kumari et al., 2011)
A meta-analysis pooled 179 associations from 80 studies of daily cortisol patterns. Flatter cortisol slopes were linked with poorer health overall (average correlation 0.147), with the strongest link for immune and inflammation outcomes (correlation 0.288). The studies used different sampling methods, and most were observational, so a flatter slope may be a marker of poor health as much as a cause. (Adam et al., 2017)
These findings help explain why a single blood cortisol value can miss the daily pattern, and why timing is so important when cortisol is measured.
Cortisol and healthy aging
Chronically high cortisol raises blood sugar, suppresses repair, fuels inflammation and is associated with shorter telomeres. A healthy daily rhythm supports healthy aging. For rhythm patterns, see cortisol patterns.
When to see a naturopathic doctor
It may be time to see a naturopathic doctor if you have fatigue, poor sleep or feel wired at night, or weight gain around the middle with high blood pressure. The same is true if chronic stress is affecting your health, or if you want cortisol results explained.
See a medical provider promptly for severe weakness, dizziness, vomiting, low blood pressure or salt cravings (possible adrenal crisis), or rapid weight gain with purple stretch marks.
Cortisol at a glance
| Topic | What the article explains |
|---|---|
| Why it matters | Blood sugar regulation; blood pressure; immune and inflammation control; energy and alertness; and sleep-wake rhythm |
| What can affect it | Time of day; stress, sleep and caffeine; medications, including steroids and birth control; and test type (blood, saliva or urine) |
| Supportive habits discussed | Morning light and a consistent sleep schedule; regular meals with protein; stress practices such as breathwork; and adaptogens with guidance |
Questions to bring to your clinician
These questions can help you get the most out of your next visit.
Does the time of day my cortisol was drawn change how we should read it?
How should I read my cortisol alongside the rest of my labs and my symptoms?
How often would it make sense to recheck my cortisol in my situation?
Which daily habits or medications could be influencing my cortisol before we retest?
Frequently asked questions
When should cortisol be tested?
Blood cortisol is usually tested in the morning. Saliva or urine tests can show the daily pattern.
What does high cortisol mean?
It can reflect stress, medications or, rarely, Cushing’s syndrome.
What does low cortisol mean?
It can signal adrenal insufficiency, which needs medical evaluation.
Is adrenal fatigue real?
It is not a recognized evaluation, but stress-related changes in cortisol rhythm are real.
Sources
- Adam EK, et al. Diurnal cortisol slopes and mental and physical health outcomes: A systematic review and meta-analysis. Psychoneuroendocrinology 2017. PMID: 28578301. https://pubmed.ncbi.nlm.nih.gov/28578301/
- Cain DW, et al. Immune regulation by glucocorticoids. Nat Rev Immunol 2017. PMID: 28192415. https://pubmed.ncbi.nlm.nih.gov/28192415/
- Kumari M, et al. Association of diurnal patterns in salivary cortisol with all-cause and cardiovascular mortality: findings from the Whitehall II study. J Clin Endocrinol Metab 2011. PMID: 21346074. https://pubmed.ncbi.nlm.nih.gov/21346074/
- Tomiyama AJ, et al. Does cellular aging relate to patterns of allostasis? An examination of basal and stress reactive HPA axis activity and telomere length. Physiol Behav 2012. PMID: 22138440. https://pubmed.ncbi.nlm.nih.gov/22138440/
- MedlinePlus: Cortisol Test
- MedlinePlus: Adrenal Gland Disorders
This article is for educational purposes only and is not medical advice. It does not replace an individual evaluation. Talk with your healthcare provider before starting supplements or changing medications, especially if you are pregnant, nursing, or managing a health condition.
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