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Hormones

Cortisol

Cortisol is the body's primary stress hormone, produced by the adrenal glands in response to physical and psychological stress. It follows a diurnal rhythm — peaking in the early morning (6-8am) to wake you up, then declining through the day. A morning blood test captures your cortisol awakening response, which is the most diagnostically useful measurement.

Optimal Ranges

Clinical (NHS) Range

166-507 nmol/L (morning)

nmol/L

Performance-Optimised Range

280-450 nmol/L (morning)

nmol/L

The clinical range defines what is considered medically “normal” — broad enough to cover 95% of the population. The performance range reflects where research and clinical experience suggest most people feel and function at their best.

Why It Matters

Why Cortisol matters for performance

Chronically elevated cortisol — from overtraining, sleep deprivation, work stress, or poor diet — drives muscle breakdown, fat storage (particularly visceral/abdominal), immune suppression, and impaired recovery. It also directly antagonises testosterone production, creating a catabolic environment that undermines training adaptations. Conversely, blunted morning cortisol (often seen in burnout or 'adrenal fatigue') leads to difficulty waking, low morning energy, and reliance on caffeine. The cortisol:DHEA-S ratio is increasingly used as a measure of stress resilience.

Symptoms

Signs your levels may be off

Low / Deficiency

  • Extreme fatigue and difficulty waking
  • Dizziness on standing
  • Salt cravings
  • Low blood pressure
  • Weight loss

High / Excess

  • Visceral fat gain (especially abdominal)
  • Insomnia and disrupted sleep
  • Anxiety and irritability
  • Muscle wasting despite training
  • Frequent illness (immune suppression)

Dietary Sources

Foods that support Cortisol levels

No dietary sources — cortisol is produced endogenouslyReduce caffeine intake (especially after 12pm)Regular meals prevent cortisol spikes from low blood sugarOmega-3 fatty acids modulate the cortisol responseDark chocolate (flavanols) may reduce cortisol reactivity

Supplementation

Evidence-based supplementation

Ashwagandha (KSM-66 extract, 600mg daily) is the most evidence-based supplement for cortisol management — a 2019 meta-analysis in Medicine showed significant cortisol reduction vs placebo. Phosphatidylserine (400mg daily) can blunt exercise-induced cortisol spikes. Magnesium glycinate (300-400mg evening) supports the parasympathetic nervous system and improves sleep quality. L-theanine (200mg) promotes calm focus without sedation. However, supplements only manage the symptom — the root causes (sleep, stress, overtraining, diet) must be addressed.

Research

Key study

An investigation into the stress-relieving and pharmacological actions of an ashwagandha extract

Lopresti AL, Smith SJ, Malvi H, et al.

Medicine (2019)

DOI: 10.1097/MD.0000000000017186

Related Biomarkers

Hormones

DHEA-Sulphate

Optimal: 7.0-12.0 µmol/L

Hormones

Total Testosterone

Optimal: 20-30 nmol/L

Vitamins & Minerals

Magnesium (Serum)

Optimal: 0.85-1.0 mmol/L

Related Guides

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8 biomarkers behind fatigue

Complete Guide to Blood Tests

What to test and why it matters

Test your Cortisol levels

Cortisol is included in the Helvy 50+ biomarker panel. Get your results in 5 days with a personalised protocol.

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This content is for educational purposes only and does not constitute medical advice. Your data suggests areas for optimisation, but any concerns should be discussed with a qualified healthcare professional. If your results flag values outside safe ranges, we recommend consulting your GP.