Cortisol is a steroid hormone produced by the adrenal glands that plays a role in regulating energy use, blood pressure, and the sleep-wake cycle. Getting 7–9 hours of regular sleep at night, maintaining a meal schedule that avoids long periods of fasting, engaging in 150 minutes of moderate-intensity activity per week, and limiting caffeine consumption to the afternoon can help keep cortisol close to its natural daily rhythm.
What Is Cortisol, and What Are Its Functions in the Body?
Cortisol is a steroid hormone produced in the outer layer of the adrenal glands located above the kidneys. Regular sleep times, a meal schedule that avoids long periods of fasting, moderate exercise, timed caffeine intake, and short rest breaks throughout the day can help keep cortisol close to its natural rhythm. It is normal for the hormone to fluctuate throughout the day. The goal is not a constant low level, but a healthy rhythm.
Cortisol production begins with signals from the hypothalamus and pituitary gland in the brain. The hypothalamus releases CRH, the pituitary gland releases ACTH, and ACTH directs the adrenal glands to produce cortisol. When cortisol levels in the blood rise, feedback reaches the same centers, and production slows. This cycle is called the HPA axis.
Cortisol’s main functions include:
- Participating in glucose production in the liver during periods of fasting to help maintain energy flow to the brain
- Playing a role in regulating blood pressure and vascular tone
- Playing a role in adjusting the intensity of the immune response
- Contributing to the alignment of the sleep-wake cycle with the internal clock
- Playing a role in reprioritizing attention and energy use in response to a sudden threat
Cortisol has a half-life in the blood of approximately 60–90 minutes. An increase caused by a single stressful event subsides within a few hours after the trigger ends. The real imbalance usually arises not from short-term increases, but from a disruption in rhythm caused by weeks of sleep deprivation and periods of continuous strain.
How Does Cortisol Change Throughout the Day?
Cortisol follows a 24-hour cycle and reaches its highest level shortly after waking. Within 30–45 minutes after waking, cortisol increases by an average of 50–75% compared to its level at the moment of waking; this increase is called the cortisol awakening response. It then gradually decreases throughout the day and reaches its lowest level around midnight.
| Time of day | Cortisol level | Effect on the body |
| 30–45 minutes after waking | Daily peak | Alertness, transition to energy use |
| Midday | Moderate | Focus and daily activity |
| 6:00–9:00 PM | Low | Transition to relaxation |
| Around midnight | Lowest | Environment suitable for deep sleep |
| After 3:00–4:00 AM | Increase again | Preparation for waking |
For serum cortisol measured in laboratories between 7:00 and 9:00 AM, the reference range is generally given as approximately 5–25 µg/dL (138–690 nmol/L). The evening value is usually half or less than the morning value. Reference ranges vary depending on the laboratory and measurement method.
A reversed rhythm—meaning low in the morning and high in the evening—is common in night shift workers and those with irregular sleep schedules. Intense screen light in the evening may also play a role in delaying melatonin release and shifting the cycle.
What Factors Affect Cortisol Levels?
Most factors affecting cortisol are daily habits: sleep duration, caffeine, exercise intensity, meal schedule, and ongoing mental load. Each stimulates the HPA axis through a different mechanism.
Sleep
The recommended sleep duration for adults is 7–9 hours at night. Research has shown that a single night of restricted sleep is associated with higher-than-normal cortisol levels the next evening. Keeping bedtime and wake-up times within a 1-hour window, even on weekends, helps maintain the regularity of the internal clock. For more information on this, you can check out the guide on how to establish a sleep routine.
Caffeine
For healthy adults, the safe upper limit for daily caffeine intake is considered 400 mg; this amount is equivalent to approximately 3–4 cups of filtered coffee. Caffeine has an average half-life of 5 hours, meaning that half of the caffeine in a coffee consumed at 4:00 PM is still in circulation at 9:00 PM. Caffeine significantly increases cortisol release, especially in people who do not consume it regularly. For the amounts found in daily sources, you can check out the page on what caffeine is and which beverages contain it.
Exercise
150 minutes of moderate-intensity activity per week is the general recommendation. Short, intense workouts cause a temporary increase in cortisol; this is the body’s normal adaptation response. However, high-intensity workouts exceeding 60 minutes every day without allowing for recovery days can make it harder to recover.
Nutrition
Since one of cortisol’s functions is to help maintain blood sugar, long periods of fasting and very low energy intake are conditions that stimulate cortisol. Meals containing protein, fiber, and complex carbohydrates can help keep blood sugar more balanced.
How Are Cortisol Levels Measured?
Cortisol can be measured in blood, saliva, and 24-hour urine samples. The choice of method depends on the question you are seeking an answer to. A single blood test only shows the level at the moment it is taken and provides limited information about the rhythm.
- Serum: Generally taken between 7:00 and 9:00 AM, it shows total cortisol, including the protein-bound portion.
- Saliva: Reflects biologically active free cortisol. A rhythm profile can be created by taking samples at four different times during the day.
- 24-hour urine: Provides the total free cortisol output for one day and is less affected by momentary fluctuations.
Medications containing estrogen can increase cortisol-binding protein, making total serum cortisol appear higher than it is. A sleepless night before a test, morning coffee, and intense exercise can also skew the results. Therefore, the results should be interpreted by the healthcare professional who ordered the test, along with the clinical picture.
What Information About Cortisol Is Incorrect?
The most common misconception about cortisol is viewing the hormone as entirely negative. Cortisol is a vital hormone, and it is difficult to start the day awake without a morning peak.
Incorrect: The lower cortisol is, the better. A lack of sufficient increase in the morning is also a sign of an imbalance in the rhythm. In assessment, the focus is not on a single number, but on the curve throughout the day.
Incorrect: A single saliva test done at home is sufficient. Because cortisol changes from hour to hour, a single sample does not show the rhythm. At least 4 time points are needed for a profile.
Incorrect: The adrenal glands get tired from stress and stop working. This description does not correspond to an accepted diagnosis in medical literature. In cases of prolonged strain, what changes is usually not the capacity of the glands, but the feedback and rhythm regulation in the HPA axis.
Incorrect: A single food or supplement determines the cortisol rhythm on its own. The cortisol rhythm is the combined result of sleep, light, meal timing, and stress load. When choosing a dietary supplement, it is a more realistic approach to examine measurable characteristics such as the form of the ingredients, dosage per serving, manufacturing certifications, and raw material source.
For Whom Is Lifestyle Adjustment Suitable, and For Whom Is It Not Enough?
Sleep, nutrition, and activity adjustments are a suitable starting point for healthy adults whose rhythm has shifted due to a demanding work pace, irregular bedtimes, or long screen time. These adjustments are free and low-risk for most people.
However, the following groups should consult a healthcare professional before making adjustments on their own:
- Those using medications containing corticosteroids in cream, spray, or tablet form; abruptly stopping these medications is risky.
- Pregnant women; cortisol naturally increases 2–3 times during pregnancy, and different reference values are used.
- Those who work continuous night shifts; light and sleep schedules should be established according to the shift schedule.
- Those who notice unexplained persistent fatigue, unexpected changes in body weight, muscle weakness, or new changes in the skin.
- Those taking more than one regular medication and individuals under the age of 18.
How to Create a Daily Plan for Cortisol Balance?
A practical way to support the cortisol rhythm is to incorporate a single habit into each part of the day. The following plan provides a general framework for healthy adults.
1. Within 30 minutes of waking, go out into the sunlight for 10–15 minutes; morning light plays a role in aligning the internal clock with the daily rhythm.
2. Drink your first coffee 60–90 minutes after waking and do not consume caffeine after 2:00 PM.
3. Eat breakfast within 2 hours of waking, including approximately 20–30 g of protein.
4. Leave a 4–5-hour gap between main meals and avoid long periods of fasting.
5. Spread out your 150 minutes of weekly activity across the days; finish intense workouts before 7:00 PM.
6. Take a 5-minute breathing break 2–3 times during the day: inhaling for 4 seconds and exhaling for 6 seconds creates a rhythm of approximately 6 breaths per minute.
7. Reduce screen brightness 60 minutes before bedtime and keep the bedroom between 18–20°C.
8. Fix your bedtime and wake-up time within a 1-hour window, including weekends.
Maintaining the plan in the same way for several weeks and recording sleep times and energy levels in short notes makes it easier to see which habit suits your personal rhythm. Implementing changes one or two steps at a time each week, rather than all at once, helps sustain new habits.
Frequently Asked Questions
What is cortisol?
Cortisol is a steroid hormone produced by the adrenal glands that plays a role in regulating energy use, blood pressure, and the sleep-wake cycle.
When is cortisol highest during the day?
Cortisol generally reaches its highest level 30–45 minutes after waking, gradually decreases throughout the day, and reaches its lowest level around midnight.
Does caffeine affect cortisol?
Caffeine can increase cortisol release, especially in people who do not consume it regularly. Since caffeine has an average half-life of 5 hours, limiting consumption in the afternoon can help regulate sleep.
How is cortisol measured?
Cortisol can be measured in blood, saliva, and 24-hour urine samples. The results should be interpreted by the healthcare professional who ordered the test, along with the clinical picture.
Who Should Consult a Healthcare Professional Before Making Adjustments Related to Cortisol?
Those using medications containing corticosteroids, pregnant women, night shift workers, individuals taking more than one regular medication, individuals under the age of 18, and those who notice unexplained persistent symptoms should consult a healthcare professional first.
