Vitamin D helps your body absorb calcium, keeps bones and muscles strong, and supports your immune system. We make most of it from sunlight on our skin — which is exactly why deficiency is so common in the UK, where sunshine is limited for much of the year. Here's how to know whether a test is worth it for you.
Who is most at risk of low vitamin D?
Deficiency can affect anyone, but the risk is higher if you:
- Spend little time outdoors, or cover most of your skin
- Have darker skin (more melanin reduces vitamin D production)
- Are pregnant or breastfeeding
- Are over 65
- Are overweight
- Have a condition affecting fat absorption (e.g. coeliac or Crohn's disease)
Signs that might prompt a test
Low vitamin D is often silent, but when symptoms appear they can include tiredness, aching bones or muscles, muscle weakness, low mood, and getting frequent infections. Because these overlap with so many other conditions, a blood test is the only way to know for sure.
What the numbers mean
Vitamin D is measured as 25-hydroxyvitamin D in nmol/L. As a general guide used in the UK:
- Below 25 nmol/L — deficient
- 25–50 nmol/L — insufficient for some people
- Above 50 nmol/L — generally considered sufficient
Your doctor will interpret your result alongside your symptoms and risk factors rather than the number alone.
Check your vitamin D level
A simple blood test measures 25-hydroxyvitamin D so you know exactly where you stand — and whether you need to top up.
Book a vitamin D testHow to correct a low level
Public Health England advises everyone in the UK to consider a daily supplement of 10 micrograms (400 IU) in autumn and winter. If a test shows you're deficient, your doctor may recommend a higher "loading" dose for a period before dropping to a maintenance dose. Sensible sun exposure in summer and vitamin-D-rich foods (oily fish, eggs, fortified foods) also help.
Testing more than vitamin D
If you're testing because of tiredness or low mood, it can be more efficient to check the other common nutrient deficiencies at the same time — B12, folate, ferritin (iron), magnesium and zinc — rather than vitamin D alone.
Check your vitamin D with OneMedicine
Book online — CQC-registered clinic in Birmingham, or a home visit / local clinic nationwide. Doctor-reviewed results, most within 24 hours.
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Specialist interest: Cardiovascular Medicine · OneMedicine, CQC-registered clinic