# 17 | The Truth About Cortisol

Type "cortisol" into any search engine and within seconds you will be met with a wave of supplements, detox protocols and morning routines promising to "fix" your stress hormone. The wellness industry has turned cortisol into a villain - something to suppress or hack your way around. The reality is both more straightforward and more interesting than that and understanding what cortisol actually does is considerably more useful than buying something to block it.

What Cortisol Actually Is

Cortisol is a hormone produced by the adrenal glands, two small glands that sit above the kidneys. It is released in response to stress but it is also essential for basic daily function where it helps regulate blood sugar, supports immune responses, reduces inflammation and plays a central role in the sleep-wake cycle. Cortisol levels are naturally highest in the morning, where they help the body wake up and become alert, and gradually decline throughout the day. This daily rhythm is normal and necessary.

The stress response that cortisol drives — often called the fight-or-flight response — exists for good reason. When the brain perceives a threat, cortisol and adrenaline are released rapidly to prepare the body to respond: heart rate increases, blood sugar rises, digestion slows and non-essential functions are temporarily put on hold. In the short term, this is not harmful. It is the body doing exactly what it is built to do.

When the Problem Starts

The issue is not cortisol itself — it is what happens when the stress response is activated repeatedly, over a long period of time, without adequate recovery. When the body is under sustained pressure, cortisol levels can remain chronically elevated and over time this has measurable consequences across multiple body systems.

Research consistently links chronically elevated cortisol to disrupted sleep, weight gain particularly around the abdomen, impaired immune function and reduced ability to regulate blood sugar. In women specifically, prolonged high cortisol can suppress the hormones that regulate the menstrual cycle, leading to irregular or absent periods. It can worsen PMS, reduce thyroid function and interfere with the production of progesterone — because when the body is under sustained stress, reproductive function is deprioritised in favour of survival.

There is also a well-established relationship between chronic stress and the gut. Elevated cortisol alters how quickly food moves through the digestive system, increases gut permeability and can disrupt the balance of gut bacteria — which, as we explored in our last journal, has its own downstream effects on hormonal health.

What "Adrenal Fatigue" Actually Means

This is where a clear line needs to be drawn. "Adrenal fatigue" — the idea that the adrenal glands become exhausted from overproducing cortisol and essentially burn out — is not a recognised medical diagnosis. It does not appear in clinical guidelines and the major endocrinology bodies globally do not support it as a condition. Studies looking for evidence of adrenal insufficiency in people diagnosed with "adrenal fatigue" by wellness practitioners have consistently failed to find it.

There is, however, a real condition called adrenal insufficiency — also known as Addison's disease — in which the adrenal glands do not produce enough cortisol. This is a serious, diagnosable medical condition with specific symptoms, blood tests and treatment. It is not the same thing as feeling exhausted after a stressful few months, and conflating the two does a disservice to people living with actual adrenal insufficiency.

The symptoms that wellness culture attributes to adrenal fatigue — tiredness, brain fog, low mood, difficulty concentrating, disrupted sleep — exist and worth taking seriously. But their causes are varied and in many cases addressable and they deserve proper investigation rather than a protocol built on a diagnosis that does not exist.

What the Evidence Actually Supports

Managing the effects of chronic stress on the body does not require a cortisol supplement, a special tea or a five-step morning routine. The interventions with the most consistent evidence behind them are also the least glamorous: adequate and regular sleep, which is one of the most powerful regulators of the cortisol rhythm; regular movement, which has been shown to reduce both perceived stress and cortisol reactivity over time; sufficient dietary protein and blood sugar stability throughout the day, which reduces the cortisol spikes that come with energy crashes; and rest — not passive screen time but activities that allow the nervous system to actually downregulate.

Certain adaptogens — plant compounds sometimes marketed for stress support — have some early-stage research behind them but the evidence base is not yet strong enough to support the claims made about most of them in the supplement market. If you are considering them, they are unlikely to cause harm in healthy individuals, but they are not a substitute for addressing the underlying source of chronic stress.

When to Seek Support

If you are experiencing symptoms that feel disproportionate to your circumstances — profound fatigue that does not improve with rest, significant mood changes, very disrupted sleep or irregular periods without an obvious cause — it is worth speaking to your GP or healthcare provider. Cortisol can be measured through blood, urine, or saliva tests and a clinician can assess whether your levels fall within a normal range and investigate further if they do not. Self-diagnosing through a wellness lens and self-treating through supplements is, at best, an expensive distraction from answers that are actually available to you.

Cortisol is not something to fear or fight but something to understand.

References

1.    Cadegiani FA, Kater CE. Adrenal fatigue does not exist: a systematic review. BMC Endocrine Disorders. 2016 Aug 24;16(1):48. doi: 10.1186/s12902-016-0128-4. PMID: 27557747; PMCID: PMC4997656. (The definitive systematic review on this topic; no subsequent review has contradicted its findings.)

2.    Padalkar P, Doshi PR, Padwal M. Investigating the relationship between cortisol, a stress marker, and immune function across age and gender. Cureus. 2025 May 28;17(5):e85009. doi: 10.7759/cureus.85009. PMID: 40585625; PMCID: PMC12205267.

3.    Garcia de Leon R, Baaske A, Albert AY, Booth A, Racey CS, Gordon S, Smith LW, Gottschlich A, Sadarangani M, Kaida A, Ogilvie GS, Brotto LA, Galea LAM. Higher perceived stress during the COVID-19 pandemic increased menstrual dysregulation and menopause symptoms. Women's Health (London). 2023;19:17455057231199051. doi: 10.1177/17455057231199051. PMID: 37665720; PMCID: PMC10478301.

4.    Whirledge S, Cidlowski JA. Glucocorticoids, stress, and fertility. Minerva Endocrinologica. 2010 Jun;35(2):109–125. PMID: 20595939; PMCID: PMC3547681. (Remains the most cited paper specifically on cortisol and reproductive suppression.)

5.    Sánchez-Borrego R et al. Diet, the gut microbiome, and estrogen physiology: a review in menopausal health and interventions. Nutrients. 2026 Mar 26;18(7):1052. doi: 10.3390/nu18071052. PMCID: PMC13074627.