Cortisol: What It Does, Why It Goes Wrong, and How to Rebalance It Through Nutrition

Cortisol is one of the most misunderstood hormones in women's health. It is essential for life, and yet chronic dysregulation of cortisol underpins a wide range of symptoms that women experience daily: fatigue, anxiety, weight gain, poor sleep, hormonal imbalance, gut problems, and impaired immune function.

Understanding cortisol and how to support its healthy regulation is foundational work for almost every complex chronic health presentation.

What Is Cortisol?

Cortisol is a glucocorticoid hormone produced by the adrenal cortex in response to signals from the hypothalamic-pituitary-adrenal (HPA) axis. It is the body's primary stress hormone, but calling it that undersells its importance. Cortisol regulates blood sugar, immune function, inflammation, metabolism, sleep-wake cycles, and blood pressure. It has receptors in virtually every tissue in the body.

Cortisol follows a diurnal rhythm: it peaks in the morning shortly after waking (the cortisol awakening response, or CAR), stimulating alertness and metabolic readiness, then declines through the day to allow sleep onset at night. This rhythm is as fundamental to health as sleep itself.

What Disrupts Cortisol?

Multiple factors disrupt cortisol's diurnal rhythm and HPA axis function:

• Chronic psychological stress

• Poor or insufficient sleep

• Blood sugar instability (hypoglycaemia triggers cortisol release)

• Over-exercising or high-intensity training without adequate recovery

• Chronic infection, inflammation, or gut dysfunction

• Nutritional deficiencies (particularly vitamin C, magnesium, B5, and zinc)

• Alcohol and caffeine in excess

• Shift work or chronic circadian rhythm disruption

• Oestrogen fluctuations in perimenopause (oestrogen influences cortisol binding proteins)

Signs of Cortisol Dysregulation

Cortisol dysregulation rarely presents as a simple "high" or "low." It typically involves a disrupted diurnal pattern:

High Cortisol Pattern

• Difficulty falling asleep despite exhaustion

• Wired but tired feeling, especially in the evening

• Anxiety, hypervigilance, and racing thoughts

• Abdominal weight gain

• Blood sugar instability: energy crashes, cravings

• Suppressed immune function with frequent illness

• Menstrual irregularities (high cortisol suppresses GnRH and disrupts the reproductive axis)

Low Cortisol Pattern (HPA Axis Hypoactivation)

• Profound, unrelenting fatigue, especially in the morning

• Difficulty waking even after adequate sleep

• Low blood pressure and dizziness on standing

• Salt cravings

• Amplified stress response to minor triggers

• Low mood, flat affect, and poor motivation

• Heightened PMDD or premenstrual symptoms

Many women cycle between both patterns, with high cortisol in the evening and low cortisol in the morning, a pattern sometimes called "blunted CAR" or HPA axis flattening [1].

Cortisol, Hormones, and Women's Health

Progesterone Steal

Chronically elevated cortisol demand can divert progesterone (which shares a common biosynthetic pathway) into cortisol production via a mechanism sometimes called "progesterone steal." While the biochemistry is more complex than a simple trade-off, the clinical outcome is functionally the same: reduced progesterone relative to oestrogen, contributing to oestrogen dominance and worsening PMDD.

Gut Function

Cortisol directly influences gut motility, intestinal permeability, and the microbiome composition. Chronic HPA activation is associated with increased intestinal permeability, SIBO risk, and dysbiosis. The relationship is bidirectional: gut dysfunction drives HPA activation through inflammatory signalling, creating a reinforcing cycle. See the full article on the gut-brain axis.

MTHFR and COMT Interactions

Cortisol regulation intersects with methylation. Women with slow COMT variants have impaired catecholamine clearance, which amplifies stress reactivity. Women with MTHFR variants may have impaired neurotransmitter synthesis that reduces stress resilience.

Nutritional Strategies for Cortisol Support

Blood Sugar Stabilisation

Every blood sugar crash triggers a cortisol spike. Protein and fat at each meal, eating every 4 to 5 hours, and eliminating late-night sugar and alcohol prevents reactive hypoglycaemia and reduces the cortisol burden.

Vitamin C

The adrenal glands have the highest concentration of vitamin C of any tissue in the body. Vitamin C is required for cortisol synthesis and for adrenal recovery post-stress. Under chronic stress, vitamin C is rapidly depleted. Supplemental vitamin C at 500 to 1000mg daily (with food) supports adrenal function [2].

Magnesium

Magnesium directly inhibits cortisol secretion from the adrenal glands and modulates GABA-A receptor function, reducing anxious arousal. Magnesium glycinate at 300 to 400mg before bed supports sleep, reduces evening cortisol, and improves HPA axis regulation.

Adaptogenic Herbs

Ashwagandha (Withania somnifera) has the strongest evidence base for cortisol reduction, with a meta-analysis of randomised controlled trials showing significant reductions in cortisol and stress scores [3]. Rhodiola rosea supports stress resilience and reduces HPA reactivity. These should be used under clinical guidance, particularly when cortisol patterns are complex.

Phosphatidylserine

Phosphatidylserine (PS) is a phospholipid that blunts the cortisol response to exercise and psychological stress. Evidence from RCTs shows that PS supplementation reduces cortisol output and improves the stress response [4]. It is particularly useful in the high-cortisol evening pattern.

Prioritise Sleep

Cortisol and sleep are tightly coupled. Disrupted cortisol impairs sleep; disrupted sleep disrupts cortisol. Supporting the circadian rhythm through consistent sleep/wake times, morning light exposure, blue light reduction in the evening, and magnesium supplementation is the most powerful single intervention for normalising cortisol patterns.

Testing Cortisol

A single blood or salivary cortisol test provides a snapshot, not a pattern. The most clinically useful assessment is a 4-point diurnal salivary cortisol test, ideally combined with DHEA-S. The DUTCH comprehensive hormone test provides cortisol metabolites alongside the full hormonal picture. See the full article on functional testing for details.

Exhausted, wired, and can't regulate your stress response?

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References

• Fries E, et al. A new view on hypocortisolism. Psychoneuroendocrinology. 2005;30(10):1010-1016. PubMed

• Peters EM, et al. Vitamin C supplementation attenuates the increases in circulating cortisol, adrenaline and anti-inflammatory polypeptides following ultramarathon running. International Journal of Sports Medicine. 2001;22(7):537-543. PubMed

• Pratte MA, et al. An alternative treatment for anxiety: a systematic review of human trial results reported for the Ayurvedic herb ashwagandha. Journal of Alternative and Complementary Medicine. 2014;20(12):901-908. PubMed

• Monteleone P, et al. Effects of phosphatidylserine on the neuroendocrine response to physical stress in humans. Neuroendocrinology. 1990;52(3):243-248. PubMed