What Is Cortisol? The Rundown On The Body’s Built-In Stress Response
How cortisol works:
- Cortisol is part of the body’s natural stress response system and helps regulate functions linked to energy, alertness, metabolism and recovery.
- Stress, sleep and cortisol are closely connected, with ongoing stress and poor sleep potentially influencing the body’s natural cortisol rhythm over time.
- High cortisol symptoms may include trouble sleeping, feeling tired but wired, brain fog, mood changes and difficulty switching off.
- Consistent sleep, balanced nutrition, regular movement and stress management practices may all help support healthy cortisol balance and overall wellbeing.
Ever feel like your brain is still racing long after the workday ends? Or like you’re tired, but somehow still running on high alert? For many people, that always-on feeling can be linked to the body’s stress response, and one of the key hormones involved is cortisol.
Often called the stress hormone, cortisol helps the body respond to pressure, stay alert and manage everyday demands. It also plays an important role in a range of different functions¹.
In this guide, we’ll break down what cortisol actually is, how the stress response works and why supporting balance matters for overall wellbeing.
What does cortisol do?
Cortisol is produced by the adrenal glands and released as part of the body’s built-in stress response system, known as the hypothalamic-pituitary-adrenal (HPA) axis. This system works closely with the brain and nervous system to help the body respond to challenges¹.
Importantly, cortisol itself is not bad. Short-term increases in cortisol are considered normal and even helpful. However, your overall wellbeing suffers when stress becomes more constant, and cortisol remains elevated for long periods of time².
Along with supporting stress response, cortisol helps regulate a range of functions, including energy production, metabolism, immune system function, blood pressure and the sleep-wake cycle³.
Assisting in energy production
One of cortisol's key jobs is helping the body manage and distribute energy. To do this, it influences how the body uses carbohydrates, fats and proteins, while also helping regulate blood sugar levels. During times of stress or increased demand, cortisol helps increase glucose availability so the body has the energy it needs to respond³. Cortisol also follows a natural daily rhythm that supports alertness during the day and recovery overnight³.
Supporting immune function
Beyond energy and sleep, cortisol helps regulate inflammation and immune function. In balanced amounts, cortisol supports the body’s ability to respond to physical and emotional stressors. It also contributes to cardiovascular function and may influence mood, focus and memory³.
Importantly, the body is designed to carefully regulate cortisol levels through a feedback system involving the brain and adrenal glands. The goal isn’t to eliminate cortisol completely, but rather to support a healthy balance over time.
What causes high cortisol?
One of the main drivers of high cortisol is chronic stress. Unlike short bursts of stress that the body can recover from relatively quickly, ongoing emotional, mental or physical stress may keep the body’s stress response system activated over time⁴.
Here are a few factors that may contribute to high cortisol levels:
- Sleep: Disrupted sleep patterns, inconsistent sleep schedules, or not getting enough quality sleep may influence cortisol regulation⁴.
- Physical activity: While movement is generally supportive for wellbeing, consistently intense exercise without enough rest and recovery may place additional stress on the body⁴.
- Diet: Irregular eating patterns or not consuming enough energy throughout the day may also affect cortisol levels, as the body works to maintain stable blood sugar and energy availability⁴.
High cortisol symptoms
Elevated cortisol levels can show up in a range of physical, mental and emotional ways. The experience can also feel different from person to person, particularly when stress has been building gradually over time.
Common signs of high cortisol may include:
- Changes in mood, including irritability, anxiety or feeling emotionally overwhelmed⁵ ⁶
- Difficulty falling or staying asleep⁶
- Feeling tired despite sleeping⁶
- Brain fog or trouble concentrating⁶
- Low motivation or feeling flat
- Changes in appetite or weight⁷
- Higher blood pressure levels⁷
It’s important to remember that many of these symptoms can overlap with other health conditions, life stages or mental health concerns. Feeling tired, stressed or emotionally flat does not automatically mean cortisol is too high. If symptoms feel ongoing or difficult to manage, speaking with a GP or qualified healthcare professional is always a good place to start.
How does high cortisol affect sleep?
Sleep and cortisol influence one another closely⁸. As part of its natural daily rhythm, cortisol gradually declines through the evening to support rest, while melatonin, the hormone involved in sleep regulation, begins to rise⁸.
When cortisol stays elevated later into the evening, that balance can be thrown off. Higher cortisol levels may suppress melatonin release, delay sleep onset and increase nighttime waking⁸. It's one of the reasons stress can leave people feeling physically exhausted but mentally wide awake at bedtime.
Over time, the two can start reinforcing each other. Poor sleep may affect the body's normal cortisol rhythm, while ongoing stress and elevated cortisol may further reduce sleep quality⁹. It's a cycle that can make it genuinely hard to feel rested, even after a full night in bed.
Cortisol levels: what's normal?
Cortisol is designed to fluctuate. Rather than sitting at one steady level, it follows a natural daily rhythm that helps regulate energy, alertness, metabolism and recovery throughout the day¹⁰.
In healthy adults, cortisol generally peaks in the morning around the time of waking, helping the body feel alert and ready for the day ahead. Levels then gradually decline across the afternoon and evening, reaching their lowest point overnight to support rest and recovery⁹ ¹⁰ ¹¹.
This rise and fall is part of the body's circadian rhythm and plays an important role in keeping multiple systems working in sync, including sleep, metabolism and energy regulation¹¹.
Because cortisol shifts throughout the day, there isn't one single number that applies to everyone. What's considered normal can depend on a range of factors, including the time of day, sleep patterns, stress levels, physical activity, medications and individual health factors.
A level that's considered normal early in the morning could look very different from what would be expected late at night.
How to check cortisol levels
If there are concerns about cortisol levels, testing is typically organised through a GP or healthcare professional. Depending on the situation, cortisol may be measured through blood, saliva12 or urine testing.
Importantly, cortisol testing is usually interpreted alongside symptoms, medical history and other health factors rather than being used as a standalone diagnosis tool.
How to lower cortisol
Supporting healthy cortisol balance is less about switching off stress completely and more about helping the body find a steady, sustainable rhythm over time. If you're looking for practical ways on how to reduce cortisol, the good news is that small, consistent habits can make a real difference.
Prioritise consistent sleep
Regular sleep patterns are one of the most practical ways to help reduce cortisol levels over time. Going to bed and waking at similar times each day, creating a calming evening routine and allowing enough time for quality sleep may all help support the body's natural recovery processes¹³.
Focus on moderate, regular movement
Physical activity can help reduce cortisol levels and support sleep quality. Research suggests regular movement may contribute to modest reductions in cortisol levels, particularly when exercise is balanced and sustainable rather than excessive¹⁴.
Moderate activities like walking, strength training, yoga or any form of movement you genuinely enjoy may all help support overall wellbeing and recovery¹⁴.
Build in stress management practices
Learning how to reduce stress doesn't require a perfectly structured routine. Practices like mindfulness, meditation, breathing exercises or simple relaxation techniques may help support the body's stress response and recovery over time¹⁵. Even short moments of pause throughout the day can give the nervous system a chance to slow down.
Support your body with balanced nutrition
Eating regularly and choosing balanced meals throughout the day may help support stable energy levels and blood sugar regulation, both of which are closely connected to cortisol. Consistent nourishment, hydration and enough overall energy intake can all help support the body during periods of increased stress or demand.
Understanding cortisol
Cortisol is often talked about as the body’s stress hormone, but its role is far more than stress alone. Cortisol plays an important role in keeping the body functioning day to day.
Like many systems in the body, cortisol works best when balance is maintained. Short-term increases are a normal and healthy part of responding to challenges, but ongoing stress, poor sleep, irregular routines and limited recovery can all influence the body’s natural cortisol rhythm over time.
Want to explore more topics linked to stress, sleep and wellbeing? Head over to the Swisse Wellness Hub and read more articles like making sense of the mental load for parents and a guide to self-care.
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