What do the numbers mean?
| 25-OH Vitamin D (nmol/L) | Label | What it means |
|---|---|---|
| Below 25 nmol/L | Deficient | High risk of bone disease, immune dysfunction, depression |
| 25–50 nmol/L | Insufficient | Symptoms likely — fatigue, low mood, muscle weakness |
| 50–75 nmol/L | Adequate | NHS minimum, but many feel better above 75 |
| 75–150 nmol/L | Optimal | Most research supports this range for overall health |
| Above 250 nmol/L | Toxicity risk | Supplement-induced excess — rare but possible |
Vitamin D is technically a hormone, not just a vitamin. It regulates calcium absorption, immune function, mood, and over 200 genes. Its effects are systemic — which is why deficiency shows up in so many different ways.
Normal vs Optimal — there is a difference
The NHS classifies 50 nmol/L as adequate. Many vitamin D researchers and endocrinologists argue the optimal range for immune function, mood, and bone health is 75–120 nmol/L.
A result of 52 nmol/L passes as normal. Yet a meaningful number of people at that level report fatigue, seasonal depression, and frequent infections. This gap between "not deficient" and "thriving" is where most people fall through the cracks.
Common symptoms you might notice
Common causes
- Limited sun exposure — the primary source of vitamin D (UK winters especially)
- Dark skin — melanin reduces UV absorption, requiring more sun exposure
- Obesity — vitamin D is fat-soluble and sequestered in adipose tissue
- Gut malabsorption — Crohn's, coeliac disease, bariatric surgery
- Kidney or liver disease — impairs conversion to the active form
- Strict vegan or vegetarian diet with no fortified foods
Questions to ask your doctor
Copy these before your next appointment. Your doctor will appreciate that you came prepared.
- My vitamin D is {value} nmol/L — what level are you aiming to get me to?
- What dose of D3 do you recommend, and should I take it with K2?
- How long until we retest, and what level would you consider optimal for me?
- Is there an underlying absorption issue we should rule out?
- Are my calcium and PTH levels normal given this vitamin D result?
Have this marker in your results?
Get your vitamin D result contextualised alongside your calcium, PTH, and other markers. Upload your full report and get a plain-English breakdown of every value — plus a personalised question list for your doctor.