Cortisol and Stress Response: What Your Body Is Trying to Tell You
- Jun 15
- 8 min read
Updated: Jun 30
Cortisol has become the villain of modern wellness, but without it, you would struggle to wake up, focus, adapt or respond to life at all. Often called the body's "stress hormone", cortisol is also considered a master hormone of the stress response because of its far-reaching influence throughout the body. Produced by the adrenal glands, it helps regulate energy, stabilise blood sugar, control inflammation, support immune function and keep your internal clock running on time.
In a UK-wide survey by the Mental Health Foundation, 74% of adults reported feeling so stressed during the previous year that they felt overwhelmed or unable to cope. Modern stress is rarely short-lived or physical. It is often continuous, low-grade and woven into everyday life through work demands, poor sleep, constant stimulation and lack of recovery.
In the right amounts, cortisol is not harmful, but instead intelligent - rising to help you perform, think clearly and meet daily demands. The problem begins when pressure never truly switches off. While symptoms vary from person to person, common signs of cortisol imbalance may include stubborn weight gain around the middle, broken sleep or waking in the early hours, fatigue, low libido, hair thinning, mood changes, irritability and difficulty maintaining stable blood sugar levels. For some women, irregular menstrual cycles or fertility challenges may also occur, sometimes reflecting changes in prolactin alongside cortisol.
What Does Cortisol Do?
Stress is not just something you feel. It is something your body actively coordinates. The moment the brain perceives pressure, whether it is an approaching deadline, poor sleep, emotional strain or intense exercise, it switches the body into a state of heightened readiness. This is often known as the "fight or flight" response, an evolutionary survival mechanism designed to help us react quickly to challenges or threats. At the centre of this process is the HPA axis, a communication network connecting the brain and adrenal glands.
Cortisol does not act alone. The same stress signals that trigger cortisol release also influence prolactin, a hormone involved in reproductive and metabolic health. In the short term, this relationship helps the body adapt to periods of increased demand. However, when stress becomes persistent, the balance can begin to shift, with prolactin levels rising alongside ongoing cortisol activation. Over time, this may contribute to symptoms such as menstrual irregularity, low libido, fatigue and changes in energy levels. This may help explain why chronic stress can sometimes be associated with symptoms that overlap with hormonal concerns. At Reborne, we routinely assess prolactin alongside cortisol, particularly in individuals experiencing symptoms that may be linked to hormone imbalance.
In healthy circumstances, this system is remarkably efficient. Cortisol rises when you need to wake up, focus, perform or respond quickly, then gradually settles once the challenge has passed. This natural rise-and-fall pattern is part of the body's built-in rhythm.
The problem is not cortisol itself. The problem is repetition without recovery. Recovery relies on activation of the parasympathetic nervous system, the body's natural "rest and digest" state, which helps lower cortisol and supports sleep, repair and restoration. When stress becomes chronic, the HPA axis can begin to lose its flexibility. Instead of rising and falling in a healthy rhythm, the stress-response system may remain activated for longer than intended or become less responsive over time. This disruption can alter cortisol timing, stress sensitivity and recovery, with effects extending far beyond moments of immediate pressure.
When Stress Starts Showing Up In Daily Life
The stress response influences multiple systems simultaneously, including the nervous system, immune system, metabolism and circadian rhythm. The brain itself is highly sensitive to stress biology, particularly areas involved in memory, emotional regulation and decision-making.
For some people, signs of high cortisol begin with energy. You sleep for enough hours but wake feeling unrefreshed, rely heavily on caffeine to function or feel strangely alert late at night despite exhaustion. Others notice changes in focus and emotional resilience, becoming more forgetful, mentally foggy or reactive to small pressures that once felt manageable. Stress can also affect the body more physically - from digestion to recovery from exercise, inflamed or dull skin, and increased frequency of minor illnesses during periods of prolonged strain. Importantly, these signs are not proof that something is “wrong” with you. More often, they are signals that the body has been adapting to demand for longer than it was designed to.
Sometimes, the most important thing the nervous system needs is not more performance, but permission to recover. Wondering how to reduce cortisol naturally? Supporting a healthier stress response is therefore not about eliminating cortisol or striving for perfect calm. Consistent sleep, exposure to morning light, restorative movement, balanced nutrition, emotional support and moments away from constant stimulation all help reinforce the message that the body is safe enough to switch out of survival mode.
Understand Your Daily Cortisol Rhythm at Reborne Longevity
Cortisol naturally follows a daily rhythm, typically higher in the morning, helping us wake, mobilise and engage with the day, before gradually declining towards its lowest levels overnight. This early rise, known as the Cortisol Awakening Response (CAR), is one of the body's most important biological signals. In a healthy system, morning cortisol increases by approximately 50-75% within the first 30-60 minutes after waking, helping regulate alertness, energy availability and circadian rhythm. Throughout the day, cortisol continues to fluctuate in smaller pulses in response to meals, physical activity, psychological demand and changing internal needs. Research published in The Journal of Clinical Endocrinology & Metabolism suggests this rhythm plays an important role in metabolic, immune, cardiovascular and cognitive regulation. This is one reason a single cortisol reading can only tell part of the story.
At our P4 medicine-led Mayfair medical clinic, cortisol testing may be used as part of a broader clinical picture to help understand how your stress system is functioning over the course of the day:
Single Blood Draw: A snapshot of cortisol at a single point in time, routinely paired with prolactin to provide additional insight into the body's stress and hormone response.
Four-Point Salivary Cortisol Panel: Measures cortisol at key points throughout the day, from waking to bedtime, helping us understand your complete daily cortisol rhythm.
Cortisol Awakening Response (CAR) Test: Assesses the critical first 30-60 minutes after waking, when cortisol should naturally rise to prepare the body for the day ahead. A blunted, delayed or exaggerated response can be one of the earliest indicators of stress-system dysregulation.
DUTCH Test: An advanced dried urine assessment that maps your full cortisol rhythm, including the Cortisol Awakening Response, while also revealing how your body metabolises and clears cortisol. Particularly valuable in complex cases, including female hormone, fatigue and metabolic health assessments.
At Reborne, results are never interpreted in isolation. We review your cortisol rhythm, prolactin levels where relevant, wider bloodwork, wearable data, symptoms, sleep patterns and lifestyle factors to understand the full picture.
At Reborne, results are interpreted alongside your symptoms, lifestyle, sleep patterns, medical history and wider diagnostic profile to build a complete picture of your health. From there, we create a personalised strategy that may include targeted nutrition, sleep optimisation, nervous system support, evidence-informed supplementation and, where clinically appropriate, additional therapeutic or intravenous interventions. The aim is not to reduce your biology to a single number, but to understand your unique stress fingerprint, how your body responds to, adapts to and recovers from demand over time.
Medical note: This article is for educational and informational purposes only and does not constitute medical advice.
FAQ
What is the HPA axis?
The HPA axis, short for the hypothalamic-pituitary-adrenal axis, is the body’s central stress-response system. It is a communication pathway between the brain and adrenal glands that helps regulate cortisol production. When the brain perceives pressure, the HPA axis signals the release of cortisol to help the body adapt and respond.
A healthy HPA axis is designed to be flexible, activating when needed and settling once the stressor has passed.
What are common high cortisol symptoms?
Signs of high cortisol can vary from person to person and may overlap with other health conditions. Some people report high cortisol symptoms such as:
Difficulty sleeping or waking feeling unrested
Feeling “tired but wired”
Increased irritability or feeling emotionally reactive
Brain fog or difficulty concentrating
Changes in appetite or cravings for sugar and caffeine
Feeling physically tense or constantly “on edge”
Slower recovery after exercise or illness
Experiencing these high cortisol symptoms does not necessarily mean cortisol is high, but they may suggest that the body’s stress-response systems would benefit from closer attention.
How to reduce cortisol naturally
A healthier cortisol rhythm is usually supported through recovery and regulation, rather than extreme restriction or “hacks”.
Research continues to explore the benefits of:
Consistent sleep and wake times
Exposure to natural morning light
Balanced nutrition and regular meals
Moderate physical activity
Stress-management techniques such as mindfulness or breathwork
Time away from constant digital stimulation
Supportive social connection and emotional recovery
For people experiencing ongoing high cortisol symptoms, a clinical assessment may help identify contributing lifestyle, metabolic or hormonal factors.
how to check cortisol levels UK?
Doing a cortisol test in the UK can be done through blood, saliva or urine testing depending on the clinical question being explored.
At Reborne Longevity, our P4 medicine-led longevity clinic in London takes a more detailed approach by assessing cortisol patterns across different points in the day, rather than relying on a single snapshot alone. This allows our clinicians to explore how cortisol rises and falls over time, helping to build a broader picture of stress physiology, circadian rhythm and recovery patterns.
Does stress always mean cortisol is high?
Not necessarily. Stress biology is complex, and cortisol patterns can vary between individuals. Some people experiencing prolonged stress may have elevated cortisol at certain times of day, while others may experience altered rhythms or reduced responsiveness over time. This is why stress-related symptoms should always be considered as part of the bigger picture rather than attributed to one hormone alone.
Cortisol and inflammation: what is the connection?
Cortisol plays an important role in regulating inflammation throughout the body. Under healthy conditions, it helps control inflammatory signalling as part of the body’s natural stress-response system. Inflammation is complex and influenced by many factors, including sleep, nutrition, physical activity, immune health and underlying medical conditions. Cortisol is therefore best understood as one part of a much broader physiological picture.
Cortisol and metabolism: how are they linked?
Cortisol is closely involved in metabolic regulation. It helps the body manage energy availability, blood sugar balance and fuel utilisation during periods of demand. When cortisol rises temporarily, it helps mobilise stored energy so the body can respond effectively to stress. However, ongoing disruption to stress physiology may influence appetite, energy patterns and metabolic processes in some individuals.
Cortisol and the immune system: what should you know?
Cortisol and the immune system are closely connected. One of cortisol’s key functions is helping regulate immune activity and maintain balance within the body’s inflammatory response. During short-term stress, this process can be adaptive and protective. Under longer periods of strain, communication between the stress-response system and immune system may become less efficient.
What is cortisol burnout?
“Cortisol burnout” is a term commonly used online to describe feelings of exhaustion, overwhelm or prolonged stress exposure. However, it is not a formal medical diagnosis. People using this term are often describing symptoms such as fatigue, poor sleep, reduced resilience, brain fog or feeling emotionally depleted after long periods of sustained demand.
Stress physiology is complex, and symptoms associated with burnout-like experiences may involve multiple biological, psychological and lifestyle factors. Rather than assuming cortisol is simply “too high” or “too low”, a more comprehensive clinical approach considers sleep, recovery, mental wellbeing, circadian rhythm, lifestyle and broader healthspan together.
References
Attia, Peter. "Stress, Cortisol, and Sleep Deprivation: An Awful Feedback Loop." Peter Attia MD. March 14, 2022. https://peterattiamd.com/stress-cortisol-and-sleep-an-awful-feedback-loop/.
Dabbs, Ryan. "Cortisol: Everything You Need to Know About the Stress Hormone." Men's Health UK. September 5, 2025. https://www.menshealth.com/uk/health/a65529006/cortisol-stress-hormone/.
Gutierrez Nunez, Sergio, Sara Peixoto Rabelo, Nikola Subotic, James Wilson Caruso, and Nebojsa Nick Knezevic. "Chronic Stress and Autoimmunity: The Role of HPA Axis and Cortisol Dysregulation." International Journal of Molecular Sciences 26, no. 20 (October 2025): 9994. https://doi.org/10.3390/ijms26209994.
Nollet, Mathieu, William Wisden, and Nicholas P. Franks. "Sleep Deprivation and Stress: A Reciprocal Relationship." Interface Focus 10, no. 3 (June 2020): 20190092. https://doi.org/10.1098/rsfs.2019.0092.
Mental Health Foundation. Stress: Are We Coping? London: Mental Health Foundation, May 2018. https://www.mentalhealth.org.uk/sites/default/files/2022-08/stress-are-we-coping.pdf.
Ring, Melinda. "An Integrative Approach to HPA Axis Dysfunction: From Recognition to Recovery." The American Journal of Medicine (2025). https://doi.org/10.1016/j.amjmed.2025.05.044.
James, Katharine Ann, Juliet Ilena Stromin, Nina Steenkamp, and Marc Irwin Combrinck. "Understanding the Relationships between Physiological and Psychosocial Stress, Cortisol and Cognition." Frontiers in Endocrinology 14 (March 2023): 1085950. https://doi.org/10.3389/fendo.2023.1085950.
Lee, Jessica H., Emily Jane Meyer, Marni Anne Nenke, Stafford L. Lightman, and David J. Torpy. "Cortisol, Stress, and Disease—Bidirectional Associations; Role for Corticosteroid-Binding Globulin?" The Journal of Clinical Endocrinology & Metabolism 109, no. 9 (September 2024): 2161–2172. https://doi.org/10.1210/clinem/dgae412.
