Helvy
Early access is openJoin the list
Vitamins & Minerals
In the UK, the standard clinical (NHS) reference range for Vitamin D (25-OH) is 30-100 nmol/L, with 100-150 nmol/L considered the performance-optimised range. A result within these ranges suggests typical status; only a qualified clinician can interpret an individual reading.
Vitamin D (25-hydroxyvitamin D) is a fat-soluble hormone precursor synthesised in the skin upon UVB exposure and obtained through diet. It plays a critical role in calcium absorption, immune regulation, and gene expression across hundreds of pathways. Blood levels of 25-OH-D are the gold standard for assessing vitamin D status.
Optimal range · UK
100-150 nmol/L
Performance-optimised band · clinical (NHS) range 30-100 nmol/L
Reference ranges for Vitamin D, not a personal result. Any individual reading should be interpreted by a qualified clinician.
Optimal ranges
| Range | Value |
|---|---|
| Clinical (NHS) reference range | 30-100 nmol/L |
| Performance-optimised range | 100-150 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
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
Low / Deficiency
High / Excess
Dietary sources
Supplementation
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
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
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-0030-1269854Test 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.
Your next step