Vitamins & minerals
Vitamin D blood test
A vitamin D blood test measures 25-hydroxyvitamin D (25-OH vitamin D), the stored form of vitamin D and the best indicator of your overall vitamin D status. It shows whether you have enough vitamin D for healthy bones, muscles and immune function, or whether you are insufficient or deficient.
- What it measures
- 25-hydroxyvitamin D (your stored vitamin D)
- Sample
- Venous blood sample
- Fasting
- Not required
- Also known as
- 25-hydroxyvitamin D, 25-OH vitamin D, vitamin D3
- Included in 57 Health tests
- 6 panels, from £135
Vitamin D reference range
Guide only| Category | Guide range |
|---|---|
| Deficient | < 25 nmol/L |
| Insufficient | 25–50 nmol/L |
| Sufficient | > 50 nmol/L |
These UK thresholds are based on 25-hydroxyvitamin D and are widely used by the NHS. Vitamin D is usually reported in nmol/L in the UK; some labs use ng/mL, where 1 ng/mL ≈ 2.5 nmol/L.
These are general UK adult guide ranges from public health sources, shown for orientation only. Reference ranges vary by laboratory, assay, age and sex, so your result is always interpreted against the range quoted by the analysing laboratory on your report.
What does a high vitamin D level mean?
A very high vitamin D is uncommon and is almost always caused by taking high-dose supplements, not by sunshine or food, as the body self-limits how much it makes from sun.
Levels above roughly 125 nmol/L are unlikely to add benefit, and true toxicity, which raises blood calcium and can cause nausea and kidney problems, generally only occurs at much higher levels from prolonged over-supplementation.
What does a low vitamin D level mean?
A low vitamin D (insufficiency or deficiency) is very common in the UK, especially over winter, and can contribute to tiredness, and bone or muscle aches and weakness.
Severe, prolonged deficiency can lead to bone problems: osteomalacia in adults and rickets in children. Risk is higher with limited sun exposure, darker skin, covering the skin, and older age.
When to consider a vitamin D test
- Persistent tiredness or low energy
- Bone or muscle aches, or muscle weakness
- Limited time outdoors, or mostly covered skin
- Darker skin tone (higher deficiency risk in the UK)
- Pregnancy, or planning a pregnancy
- Osteoporosis or bone-health concerns
- Checking a level before or after starting supplements
Frequently asked questions
This page is general information about a blood marker and is not medical advice or a diagnosis. A vitamin D test screens and gives context; results are interpreted by a clinician alongside your symptoms, history and other markers. Always follow the guidance on your own report.