What cortisol does in the short term

Cortisol is produced by the adrenal glands through the HPA axis, which stands for hypothalamic-pituitary-adrenal axis. In acute stress, it helps mobilise energy, raise blood glucose, increase alertness, regulate inflammation and redirect resources towards survival. This is useful short-term physiology. The body borrows energy from tomorrow to deal with today.

The issue is when tomorrow keeps getting billed.

 

What does chronic stress do to the body?

Chronic stress can affect almost every major system in the body, including metabolism, cardiovascular health, immune function, sleep, digestion, reproductive hormones, mood and cognition. In the short term, the stress response is protective. It helps the body respond to danger by increasing alertness, raising blood glucose and mobilising energy. But when this response stays activated for too long, the same biological mechanisms that once protected us can begin to contribute to inflammation, metabolic dysfunction, poor sleep, hormonal disruption and increased disease risk (McEwen, 1998; Mariotti, 2015).

Cortisol is often described as the “stress hormone”, but that makes it sound more sinister than it really is. Cortisol is essential for life. It helps regulate blood pressure, inflammation, immune activity, glucose metabolism, sleep-wake timing and energy availability. The issue is not cortisol itself, but chronic cortisol dysregulation, where cortisol is persistently elevated, poorly timed, flattened across the day or no longer responding normally to the body’s feedback systems (Hirotsu, Tufik and Andersen, 2015; Nicolaides et al., 2020).

What is cortisol and why does it matter?

Cortisol is a glucocorticoid hormone produced by the adrenal glands. Its release is controlled by the hypothalamic-pituitary-adrenal axis, usually shortened to the HPA axis. When the brain detects a threat, the hypothalamus signals the pituitary gland, which then signals the adrenal glands to release cortisol.

In a healthy rhythm, cortisol usually peaks in the morning to help us wake up, then gradually declines throughout the day. This daily pattern supports energy, focus, metabolism and sleep timing. However, chronic stress, poor sleep, illness, trauma, shift work, overtraining, under-fuelling and psychological strain can all disrupt this rhythm (Androulakis et al., 2021).

Definition:
Chronic cortisol dysregulation refers to an abnormal long-term stress hormone pattern. This may involve persistently high cortisol, low morning cortisol, high evening cortisol, a flattened daily rhythm or impaired feedback from the brain and immune system.

Is high cortisol always bad?

No. Cortisol is not inherently bad. A short-term cortisol rise is normal and beneficial during exercise, illness, acute stress, low blood sugar or waking in the morning. Problems are more likely when cortisol remains elevated or poorly regulated over time.

This distinction matters because many people search for “how to lower cortisol”, but the goal is not to crush cortisol into the basement. The goal is to restore a healthy rhythm: appropriately high in the morning, appropriately low at night, and responsive to genuine physiological demand. Cortisol should behave like a well-trained guard dog, not a smoke alarm screaming at toast.

 

 

Long-term implications of chronic stress and cortisol dysregulation

1. Chronic stress can increase blood pressure and cardiovascular risk

Long-term stress activates both the HPA axis and the sympathetic nervous system. This can increase heart rate, blood pressure, vascular tone and inflammatory signalling. Over time, chronic stress exposure has been associated with higher risk of hypertension, cardiovascular disease, heart attack and stroke (Steptoe and Kivimäki, 2012; Mayo Clinic, 2024).

This does not mean stress alone “causes” heart disease. Cardiovascular risk is multifactorial and includes genetics, age, cholesterol, ApoB, blood pressure, smoking, diabetes, inflammation, body composition, diet and physical activity. However, chronic stress can amplify several of these risk pathways by increasing blood pressure, worsening sleep, affecting glucose regulation and encouraging coping behaviours such as alcohol intake, overeating or inactivity (American Psychological Association, 2018).

Summary:
Chronic stress may increase cardiovascular risk by raising blood pressure, increasing sympathetic nervous system activity, worsening inflammation and indirectly influencing behaviours that affect heart health.

2. High cortisol can contribute to blood sugar imbalance and insulin resistance

Cortisol helps raise blood glucose by stimulating glucose production in the liver and reducing glucose uptake in some tissues. This is useful in acute stress because it gives the body fast access to energy. But when cortisol remains elevated for long periods, it can contribute to higher glucose levels, increased insulin demand and reduced insulin sensitivity (Hirotsu, Tufik and Andersen, 2015).

Over time, chronic stress may therefore contribute to metabolic dysfunction, especially in people already at risk of insulin resistance, prediabetes, type 2 diabetes, abdominal weight gain, poor sleep or low physical activity. Research has linked chronic stress biology with obesity, metabolic syndrome and cardiovascular disease risk, partly through glucocorticoid and inflammatory pathways (Mariotti, 2015; Cohen et al., 2012).

Relevant biomarkers: fasting glucose, HbA1c, fasting insulin, HOMA-IR, triglycerides, HDL cholesterol, ApoB, hs-CRP.

3. Chronic stress may promote abdominal fat gain and metabolic syndrome

Persistently elevated cortisol can influence appetite, cravings, insulin signalling and fat distribution. Cortisol has been associated with increased preference for calorie-dense foods and greater central adiposity, particularly when combined with poor sleep and high perceived stress (Adam and Epel, 2007).

This is one reason some people under long-term stress feel as if their body has become metabolically “sticky”. They may not simply be lacking willpower. Their biology may be nudging them towards higher appetite, poorer glucose control, reduced satiety and altered fat storage.

Summary:
Chronic stress can make weight management harder by affecting appetite, blood sugar, insulin sensitivity, sleep quality and abdominal fat distribution.

4. Long-term stress can weaken immune defence and increase inflammation

Cortisol normally helps regulate inflammation. In the short term, this can be useful. But chronic stress may lead to glucocorticoid receptor resistance, where immune cells become less responsive to cortisol’s anti-inflammatory signals. This can result in a paradoxical state where cortisol is high or dysregulated, yet inflammation remains elevated (Cohen et al., 2012).

Chronic stress has also been linked to altered immune cell activity, increased susceptibility to infections, slower wound healing and disrupted inflammatory control (Alotiby, 2024; Nunez et al., 2025).

This is where the phrase “stress lowers immunity” becomes a little too simplistic. More accurately, chronic stress can dysregulate immunity, meaning some immune responses may be suppressed while inflammatory signalling becomes harder to control.

Relevant biomarkers: hs-CRP, white blood cell count, neutrophils, lymphocytes, vitamin D, ferritin, thyroid antibodies where clinically appropriate.

5. Cortisol dysregulation can disrupt sleep and circadian rhythm

Cortisol and sleep have a two-way relationship. Poor sleep can increase HPA axis activity, and chronic stress can disrupt sleep by increasing evening arousal, reducing sleep depth and interfering with the normal decline in cortisol at night (Hirotsu, Tufik and Andersen, 2015; Nicolaides et al., 2020).

A healthy cortisol rhythm supports waking and daytime energy. A disrupted rhythm can contribute to feeling “tired but wired”, struggling to fall asleep, waking in the night, waking unrefreshed or experiencing energy crashes during the day.

This can create a fairly unpleasant loop:

stress → poor sleep → higher cortisol output → worse glucose control → more cravings → more inflammation → more stress

A tiny biochemical hamster wheel, but with worse lighting.

6. Chronic stress can affect mood, memory and cognitive function

The brain is highly sensitive to chronic stress. The hippocampus, amygdala and prefrontal cortex are particularly involved in memory, emotional regulation, threat detection and decision-making. Long-term HPA axis dysregulation has been associated with anxiety, depressive symptoms, poorer concentration, impaired memory and reduced emotional resilience (Knezevic et al., 2023; Lei et al., 2025).

This does not mean cortisol is the sole cause of mental health issues. Mood and cognition are influenced by psychological, social, biological and environmental factors. However, chronic stress can create a physiological background state that makes calm, focus and emotional regulation harder to sustain.

Summary:
Chronic stress can affect the brain by altering HPA axis activity, inflammation, sleep and neurotransmitter-related pathways, which may contribute to anxiety, low mood, poor focus and memory problems.

7. Stress can affect sex hormones, fertility and reproductive health

The stress response can influence the hypothalamic-pituitary-gonadal axis, which regulates reproductive hormones. When the body perceives long-term threat, it may down-prioritise reproduction, growth and repair.

In women, chronic stress may contribute to menstrual irregularity, altered ovulation, worsened PMS symptoms and changes in reproductive hormone patterns. In men, chronic stress has been associated with lower testosterone, reduced libido and impaired reproductive function, although the relationship is complex and influenced by sleep, weight, alcohol, medication, illness and age (Whirledge and Cidlowski, 2010).

In plain English: the body may not prioritise reproduction when it thinks you are being chased by a metaphorical tiger every day.

Relevant biomarkers: oestradiol, progesterone, FSH, LH, prolactin, testosterone, free testosterone, SHBG, DHEA-S, cortisol, TSH, FT4, FT3.

8. Chronic stress can affect thyroid function

The thyroid system is closely connected with energy metabolism, inflammation, illness, nutrient status and stress physiology. Chronic stress may influence thyroid hormone conversion, thyroid signalling and immune function, although thyroid dysfunction should never be assumed to be “just stress”.

For someone experiencing fatigue, weight changes, low mood, poor cold tolerance, hair shedding, constipation, palpitations or menstrual changes, thyroid testing may help distinguish stress-related symptoms from thyroid disease or autoimmune thyroid conditions.

Relevant biomarkers: TSH, free T4, free T3, thyroid peroxidase antibodies and thyroglobulin antibodies, where appropriate.

9. Chronic stress can affect digestion and gut health

Stress can alter gut motility, gastric acid secretion, gut barrier function, microbiome composition and immune activity in the gut. This is one reason chronic stress can worsen symptoms such as bloating, abdominal pain, reflux, diarrhoea, constipation and IBS-like symptoms (Mayer, 2011; Mariotti, 2015).

The gut and brain communicate through the gut-brain axis, involving the nervous system, immune system, endocrine signals and microbial metabolites. Stress is not “all in the head”. It can quite literally reach the gut via nerves, hormones and inflammatory signalling.

10. Long-term cortisol elevation may impair recovery, muscle and bone health

Cortisol is catabolic, meaning it helps break down stored energy and tissue when needed. In short bursts, this is normal. However, prolonged cortisol exposure can interfere with muscle repair, collagen turnover, bone remodelling and recovery from exercise or injury (McEwen, 1998; Chrousos, 2009).

This is particularly relevant for active people who train hard, sleep poorly and under-fuel. Over time, high stress load can contribute to reduced training adaptation, slower recovery, increased injury risk and a sense of “doing everything right” but still feeling depleted.

Relevant biomarkers: vitamin D, magnesium, ferritin, full blood count, CRP, testosterone, thyroid markers, cortisol, HbA1c.

 

What are the symptoms of high cortisol or chronic stress?

Common symptoms associated with chronic stress or cortisol dysregulation may include:

• difficulty sleeping or waking through the night
• feeling tired but wired
• anxiety, irritability or low mood
• brain fog or poor concentration
• headaches or muscle tension
• increased cravings or appetite changes
• abdominal weight gain
• blood sugar swings
• digestive symptoms
• low libido
• irregular periods
• poor exercise recovery
• frequent illness or slow recovery

These symptoms are non-specific, which means they can also be caused by thyroid disorders, anaemia, diabetes, vitamin deficiencies, hormonal changes, infection, inflammatory conditions, medication effects or mental health conditions. That is why testing can be useful: it helps move from guessing to evidence.

 

Can you test cortisol?

Yes, cortisol can be tested, but interpretation depends heavily on timing and context. Cortisol follows a daily rhythm, so a single measurement may not tell the full story. Morning cortisol, evening cortisol, salivary cortisol, blood cortisol and urinary cortisol can all provide different types of information.

For general health optimisation, cortisol is often most useful when interpreted alongside related biomarkers such as:

• HbA1c and glucose
• fasting insulin and HOMA-IR
• hs-CRP
• lipid profile and ApoB
• thyroid markers
• sex hormones
• vitamin D, B12, folate, ferritin and magnesium
• full blood count
• liver and kidney function

This gives a broader picture of how stress may be interacting with metabolism, inflammation, hormones and recovery.

 

The key takeaway

Chronic stress is not just a feeling. It can leave a measurable biological footprint.

Long-term cortisol dysregulation may contribute to: blood sugar imbalance, insulin resistance, abdominal fat gain, high blood pressure, inflammation, immune disruption, poor sleep, low mood, impaired recovery, digestive symptoms and hormonal changes. The body can cope beautifully with short bursts of stress. It is the long, unrelenting drip-feed that becomes biologically expensive.

From a preventative health perspective, the goal is not simply to “feel less stressed”. It is to understand how stress is affecting the body and whether it is showing up in measurable biomarkers.

That is where health testing becomes powerful. It can help turn a vague feeling of “something is off” into objective data, clearer direction and a more targeted plan of action.

 

Stress & Cortisol FAQs

What does high cortisol do to the body long term?

Long-term high cortisol may affect blood sugar regulation, blood pressure, inflammation, sleep, immune function, weight regulation, mood, digestion and reproductive hormones. Chronic cortisol dysregulation has been associated with increased risk of metabolic syndrome, cardiovascular disease, sleep disturbance, anxiety, depression and immune imbalance (Mariotti, 2015; Cohen et al., 2012).

Can chronic stress cause inflammation?

Yes. Chronic stress may contribute to inflammation by causing glucocorticoid receptor resistance, where immune cells become less sensitive to cortisol’s anti-inflammatory effects. This can make it harder for the body to regulate inflammatory responses effectively (Cohen et al., 2012).

Can stress raise blood sugar?

Yes. Cortisol helps raise blood glucose during stress by increasing glucose production and changing insulin sensitivity. In chronic stress, this may contribute to blood sugar instability and insulin resistance, particularly in people already at risk of metabolic dysfunction (Hirotsu, Tufik and Andersen, 2015).

Can stress affect hormones?

Yes. Chronic stress can influence reproductive hormones, thyroid signalling and adrenal hormones through interactions between the HPA axis, thyroid axis and reproductive axis. This may contribute to menstrual changes, low libido, altered testosterone, fatigue and fertility-related symptoms, although other medical causes should also be considered.

Can stress affect sleep?

Yes. Cortisol helps regulate the sleep-wake cycle. Chronic stress can disrupt the normal cortisol rhythm, particularly if cortisol remains high in the evening. This may contribute to difficulty falling asleep, waking during the night or feeling unrefreshed in the morning (Nicolaides et al., 2020).

What biomarkers can show the effects of chronic stress?

Useful biomarkers may include cortisol, HbA1c, glucose, fasting insulin, HOMA-IR, hs-CRP, lipid profile, ApoB, thyroid markers, sex hormones, vitamin D, ferritin, magnesium, full blood count, liver function and kidney function. These do not “diagnose stress”, but they can show how stress may be affecting metabolism, inflammation, hormones and recovery.