Optimal Ranges
What is the optimal range for Cortisol?
Clinical (NHS) Range
166-507 nmol/L (morning)
nmol/L
Performance-Optimised Range
280-450 nmol/L (morning)
nmol/L
| Range | Value | Unit |
|---|---|---|
| Clinical (NHS) reference 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. 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
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
What are the symptoms of low or high Cortisol?
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
Which foods support Cortisol levels?
Supplementation
How do you improve Cortisol levels?
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
How is Cortisol tested in the UK?
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
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.0000000000017186Related Biomarkers
Related Guides
Explore Cortisol in depth
Test your Cortisol levels
Cortisol is included in the Helvy 50+ biomarker panel. Get your results in 5 days with a personalised protocol.
Order Your TestThis 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.