What the value means
The test measures 25-hydroxyvitamin D; 1 ng/mL equals 2.5 nmol/L. Cut-offs differ between laboratories and professional bodies: the US National Academy of Medicine considers 50 nmol/L (20 ng/mL) adequate for most people, while an older Endocrine Society guideline used 75 nmol/L (30 ng/mL). The updated 2024 Endocrine Society guideline no longer sets a fixed target for healthy adults, because large trials such as VITAL did not show a clear benefit of high doses for the heart or cancer in people without deficiency. A “normal” value is therefore not a single exact number. Your level is adequate but with little reserve – in Central Europe the sun barely supplies the skin from October to March.
Possible causes
- Season – levels naturally fall in winter and spring.
- Little time outdoors – office work, sunscreen, covered skin.
- Higher body weight – vitamin D is stored in fat tissue, so blood levels tend to be lower.
- Age and darker skin – the skin produces vitamin D less efficiently.
- Diet – there are few natural sources, mainly oily fish and eggs.
What you can do
- Sensible sun – from spring to autumn, short periods outdoors with bare arms, without burning.
- Diet – oily fish (salmon, sardines, mackerel), eggs, fortified foods.
- Supplements – modest vitamin D3 supplementation in winter is a common and safe choice; follow the label, do not exceed the EFSA upper limit and discuss higher doses with your doctor.
- Follow-up – if you start supplementing, you can recheck after 2–3 months, ideally at the same laboratory.
When to see a doctor
See a doctor if you have osteoporosis, frequent fractures, kidney, liver or bowel disease, take medicines that affect vitamin D metabolism, are pregnant, or have bone pain and muscle weakness. With parathyroid disorders or raised calcium, do not take vitamin D on your own.