Optimal Ranges
What is the optimal range for Vitamin D?
Clinical (NHS) Range
30-100 nmol/L
nmol/L
Performance-Optimised Range
100-150 nmol/L
nmol/L
| Range | Value | Unit |
|---|---|---|
| Clinical (NHS) reference range | 30-100 nmol/L | nmol/L |
| Performance-optimised range | 100-150 nmol/L | 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 Vitamin D matters for performance
Vitamin D is one of the most common deficiencies in the UK, particularly during autumn and winter when UVB exposure drops to near zero. For men focused on performance, suboptimal vitamin D is linked to reduced testosterone production, impaired muscle protein synthesis, and slower recovery from training. Studies consistently show that men with levels above 40 ng/mL have higher free testosterone and better muscular function than those in the low-normal range.
Symptoms
What are the symptoms of low or high Vitamin D?
Low / Deficiency
- Fatigue and low energy
- Muscle weakness and aches
- Low mood and seasonal depression
- Frequent illness and slow recovery
- Bone pain and stress fractures
High / Excess
- Nausea and vomiting
- Kidney stones
- Hypercalcaemia (elevated calcium)
- Confusion and disorientation
Dietary Sources
Which foods support Vitamin D levels?
Supplementation
How do you improve Vitamin D levels?
Vitamin D3 (cholecalciferol) is the preferred form, dosed at 1,000-4,000 IU daily depending on baseline levels. Co-supplementation with vitamin K2 (MK-7) is recommended to direct calcium into bones rather than soft tissue. Fat-soluble — take with a meal containing dietary fat for optimal absorption. Retest at 90 days to confirm response.
Testing
How is Vitamin D tested in the UK?
Vitamin D 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 (30-100 nmol/L) and the performance-optimal range (100-150 nmol/L), 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
Effect of vitamin D supplementation on testosterone levels in men
Pilz S, Frisch S, Koertke H, et al.
Hormone and Metabolic Research (2011)
DOI: 10.1055/s-0030-1269854Related Biomarkers
Related Guides
Explore Vitamin D in depth
Test your Vitamin D levels
Vitamin D 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.