Helvy
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Hormones
In the UK, the standard clinical (NHS) reference range for Cortisol is 166-507 nmol/L (morning), with 280-450 nmol/L (morning) considered the performance-optimised range. A result within these ranges suggests typical status; only a qualified clinician can interpret an individual reading.
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 range · UK
280-450 nmol/L (morning)
Performance-optimised band · clinical (NHS) range 166-507 nmol/L (morning)
Reference ranges for Cortisol, not a personal result. Any individual reading should be interpreted by a qualified clinician.
Optimal ranges
| Range | Value |
|---|---|
| Clinical (NHS) reference range | 166-507 nmol/L (morning) |
| Performance-optimised range | 280-450 nmol/L (morning) |
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. A result in either range suggests typical status and is not a diagnosis; any individual reading should be interpreted by a qualified clinician.
Why it matters
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
Low / Deficiency
High / Excess
Dietary sources
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.
Testing
Cortisol is measured from a blood sample. With Helvy, that means a finger-prick kit taken at home and posted to a UKAS-accredited UK laboratory, with results in around 5 days, reviewed by a qualified clinician. Your result is reported against both the clinical range (166-507 nmol/L (morning)) and the performance-optimal range (280-450 nmol/L (morning)), so you can see not just whether you are “normal” but whether you are optimal. If you make a change, retest after 8-12 weeks to confirm it worked.
Research
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.0000000000017186Test for this
Related biomarkers
Related guides
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.
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