Optimal Ranges
Clinical (NHS) 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.
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
Signs your levels may be off
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
Foods that support Vitamin D levels
Supplementation
Evidence-based supplementation approach
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.
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
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.