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Vitamin D (25-OH)

25-hydroxyvitamin D, the circulating storage form of vitamin D and the standard way to judge vitamin D status. It reflects both what the skin made from sunlight and what came from food or supplements over the preceding weeks. The active hormone (1,25-dihydroxyvitamin D) is not used for this purpose, because it can stay normal while stores are empty.

General information only — not a diagnosis, not treatment and not a substitute for your doctor. Reference ranges differ between laboratories, so the range printed on your own report is the one that counts, and only a clinician who knows your history can say what a result means for you. Never start, stop or change a medicine or supplement based on this page.

Usual adult reference range

The ranges below are typical adult reference intervals. Your own laboratory sets its own, printed next to your result, and that is the one to compare against.

Source: Widely used status thresholds published by public health bodies and clinical laboratories; the exact cut-offs differ between countries and assays. · checked 2026-09-02

What a high result generally indicates

Very high levels essentially only occur with high-dose supplementation; sunlight does not cause vitamin D toxicity. The concern at extreme levels is raised blood calcium. Ordinary supplement doses do not produce this, but the number is worth a conversation if you are taking a high-dose preparation.

What a low result generally indicates

Low vitamin D is extremely common at northern latitudes between autumn and spring, and is usually about sunlight rather than diet. Severe, prolonged deficiency causes bone disease — rickets in children, osteomalacia in adults. Milder deficiency is often symptomless, which is why it is found on a blood test rather than noticed.

These are general patterns, not a diagnosis. Many things cause a high or low result, and the same figure means different things in different people. What yours means is a question for the doctor who ordered the test.

What affects this result

• Season and latitude dominate: in Estonia and Finland the skin makes almost none from October to March.
• Skin pigmentation, sunscreen use and time spent indoors all reduce synthesis.
• Body weight — vitamin D distributes into fat tissue, lowering the blood level.
• Oily fish, egg yolk and fortified products are the main dietary sources.
• Malabsorption (coeliac disease, Crohn's, bariatric surgery) reduces uptake.
• Some medicines, including certain anti-epileptics, increase its breakdown.

Before the test

No fasting needed. The season the sample was taken in matters more than the time of day.

Any preparation instruction that comes with your test slip overrides this general note — follow the one your clinician or laboratory gave you.

The one thing to take from this page

The range above is a typical interval for orientation. Your own laboratory's range, printed beside your result, is the one that applies to you — and a result is only meaningful alongside your symptoms, your history, your medicines and your other tests. That reading is a clinician's job. This page cannot diagnose anything, cannot tell you to change a medicine or a supplement, and is not a substitute for the person who ordered your test.

Frequently asked questions

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