← All Tests
Vitamin Test

Vitamin D (25-OH Vitamin D)

Vitamin D is essential for strong bones, immunity and muscle function. Here's exactly what your test number means and what to do about it.

Written and clinically reviewed by Suman Konda, PharmD, Clinical Pharmacist · Based on peer-reviewed sources · Editorial policy · Not medical advice

Last reviewed and updated: · How we check our content

What is a Vitamin D test?

The Vitamin D test measures 25-hydroxyvitamin D (25-OH Vitamin D) in your blood: the main form your body stores. Vitamin D deficiency is extremely common worldwide, affecting an estimated 1 billion people, largely due to indoor lifestyles, darker skin pigmentation and dietary habits. The test is a simple blood draw and results are reported in ng/mL or nmol/L.

Vitamin D Normal Range Chart

LevelValue (ng/mL)Value (nmol/L)Interpretation
Severely Deficient< 10< 25Very Low
Deficient10 – 2025 – 50Low
Insufficient20 – 3050 – 75Below Optimal
Sufficient / Normal30 – 10075 – 250Normal
Toxicity risk> 100> 250Too High
Vitamin D (25-OH Vitamin D): reference intervals by group (ng/mL)A bar for each group showing its reference interval on a shared scale. The same figures appear in the table above.1285582109Deficient10–20Insufficient20–30Sufficient / Normal30–100ng/mL
Vitamin D (25-OH Vitamin D): reference intervals by group (ng/mL), drawn from the table above. Intervals differ between laboratories: compare your result against the range printed on your own report.

What does LOW Vitamin D mean?

LOW Vitamin D below 20 ng/mL: Deficiency

Low Vitamin D is called deficiency. Common causes include limited sun exposure, covering skin fully outdoors, vegetarian/vegan diet (few natural food sources), obesity (Vitamin D gets stored in fat), kidney or liver disease that prevents activation, and malabsorption conditions like coeliac disease. Symptoms can include bone pain, muscle weakness, fatigue and frequent infections: but many people have no symptoms at all.

What does very low Vitamin D mean?

LOW Vitamin D below 10 ng/mL: Severe Deficiency

Severe deficiency can lead to rickets in children (soft, deformed bones) and osteomalacia in adults (bone pain and muscle weakness). At this level your doctor will usually prescribe high-dose Vitamin D supplements (often 60,000 IU weekly for several weeks) followed by a maintenance dose.

What does HIGH Vitamin D mean?

HIGH Vitamin D above 100 ng/mL: Toxicity Risk

Vitamin D toxicity (hypervitaminosis D) is rare and almost always caused by taking very high supplement doses for a long time: not from sun exposure. It causes too much calcium to build up in the blood (hypercalcaemia), leading to nausea, weakness, frequent urination, kidney stones and, in severe cases, heart problems. Stop supplements and consult your doctor.

How to improve low Vitamin D

Your doctor will typically recommend one or more of these approaches:

  • Supplements: Cholecalciferol (Vitamin D3) tablets or sachets. Doses and duration depend on how low your level is.
  • Sun exposure: 15–30 minutes of midday sun on arms and legs (without sunscreen) several times a week helps, but results vary by skin tone and latitude.
  • Diet: Fatty fish (salmon, mackerel), egg yolks, fortified milk and cereals contain some Vitamin D, though diet alone rarely corrects a deficiency.
  • Follow-up test: After 3 months of treatment your doctor will recheck levels to see if they've improved.

Questions to ask your doctor

  • What dose of Vitamin D should I take and for how long?
  • Should I also check my calcium and parathyroid hormone (PTH)?
  • When should I get a repeat test?
  • Do I need Vitamin D3 alone or combined with Vitamin K2?

Why vitamin D deficiency is so common

Vitamin D is made in the skin through sunlight exposure, but modern indoor lifestyles, northern latitudes, darker skin, covering up, and older age all reduce how much we produce. Because very few foods contain much vitamin D, deficiency is widespread: affecting a large share of the population, particularly in winter.

The blood test measures 25-hydroxyvitamin D, the best marker of your overall stores. Levels below 25 nmol/L indicate deficiency, 25–50 nmol/L insufficiency, and above 50 nmol/L is generally considered adequate, with an optimal range often quoted as 75–120 nmol/L.

What deficiency does to the body

Vitamin D is essential for absorbing calcium and keeping bones strong. Severe, prolonged deficiency causes rickets in children and osteomalacia (soft, painful bones) in adults, and it contributes to osteoporosis and fracture risk.

Milder deficiency is often linked with tiredness, muscle aches and low mood, and vitamin D also plays a role in immune function, though supplementing beyond correcting a deficiency has not been shown to provide extra benefit for most people.

Correcting and maintaining healthy levels

Deficiency is treated with a course of higher-dose vitamin D (for example a loading regimen), followed by a lower daily maintenance dose. In many countries a daily supplement of around 10 micrograms (400 IU) is recommended for everyone during autumn and winter.

Sensible sunlight exposure in summer and eating oily fish, eggs and fortified foods also help. Because vitamin D is fat-soluble and stored, very high doses over long periods can cause harm, so it is best to supplement to correct a measured deficiency rather than taking excessive amounts.

Frequently Asked Questions

Do I need to fast for a vitamin D test?
No. Vitamin D testing does not require fasting and can be done at any time of day.
Can I get enough vitamin D from food alone?
It is difficult, as few foods are naturally rich in vitamin D. Sunlight and supplements are the main reliable sources for most people, especially in winter.
How long does it take to correct a deficiency?
With appropriate supplementation, levels usually improve over 6–12 weeks, after which a maintenance dose keeps them stable.
Can you take too much vitamin D?
Yes. Excessive long-term high-dose supplements can raise calcium to harmful levels. Stick to recommended doses unless a doctor is treating a diagnosed deficiency.

What current guidelines say about routine testing

Evidence on vitamin D testing has shifted in recent years. The 2024 Endocrine Society clinical practice guideline reviewed randomised trial evidence and suggests against routine 25(OH)D testing in the general healthy population, because no clear target level for disease prevention has been established in people without a specific indication.

Testing remains appropriate where there is a genuine clinical reason, for example symptoms of deficiency, bone disease, malabsorption conditions such as coeliac disease, chronic kidney or liver disease, or before starting treatment for osteoporosis. The same guideline does support empiric supplementation without testing for certain groups, including children and adolescents, adults over 75, those who are pregnant, and people with high-risk prediabetes.

Practical takeawayIf you have no symptoms and no risk factors, a daily supplement during autumn and winter is generally more useful than a blood test. If you do have symptoms or a relevant medical condition, testing is worthwhile: discuss it with your doctor.

References

The clinical information on this page is based on peer-reviewed sources indexed in PubMed, the biomedical literature database of the US National Library of Medicine.

  1. Demay MB, Pittas AG, Bikle DD, et al.. Vitamin D for the prevention of disease: an Endocrine Society clinical practice guideline. J Clin Endocrinol Metab. 2024;109(8):1907-1947. doi:10.1210/clinem/dgae290 · PMID 38828931
  2. Pludowski P, Holick MF, Grant WB, et al.. Vitamin D supplementation guidelines. J Steroid Biochem Mol Biol. 2017;175:125-135. doi:10.1016/j.jsbmb.2017.01.021 · PMID 28216084
  3. Vitamin D. In: StatPearls. Treasure Island (FL): StatPearls Publishing. NCBI Bookshelf NBK441912

Related reading

Medical Disclaimer: This page is for general educational purposes only. Vitamin D reference ranges may vary slightly between laboratories. The information here does not constitute medical advice and is not a substitute for consultation with a qualified doctor. Always discuss your reports with your physician before making any health decisions.