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Biomarker library / Vitamins and minerals

Vitamin D (25-hydroxyvitamin D) (25(OH)D)

Also called 25-OH vitamin D, calcidiol, vitamin D blood test

The blood test measures 25-hydroxyvitamin D, the storage form your liver makes from vitamin D produced in skin or taken in food and supplements. It reflects your overall vitamin D supply over recent weeks.

Written by the VitalDecades editorial team Reviewed by the editorial review process Updated

01  /  Reference ranges

What counts as normal

Scale in ng/mL. Cut points from the sources listed below.
Population Adults
Category Deficient
Range under 12 ng/mL Under 30 nmol/L. Associated with rickets and osteomalacia.
Source NIH Office of Dietary Supplements, Vitamin D Fact Sheet for Health Professionals (NASEM cutoffs)

Effective

Population Adults
Category Inadequate for bone and overall health
Range 12 or higher and under 20 ng/mL 30 to under 50 nmol/L.
Source NIH Office of Dietary Supplements, Vitamin D Fact Sheet for Health Professionals (NASEM cutoffs)

Effective

Population Adults
Category Adequate for bone and overall health
Range 20 to 50 ng/mL 50 to 125 nmol/L.
Source NIH Office of Dietary Supplements, Vitamin D Fact Sheet for Health Professionals (NASEM cutoffs)

Effective

Population Adults
Category Linked to potential adverse effects
Range over 50 ng/mL Above 125 nmol/L; usually from high-dose supplements.
Source NIH Office of Dietary Supplements, Vitamin D Fact Sheet for Health Professionals (NASEM cutoffs)

Effective

Normal vs optimal

Adequate for bone and overall health is 20 ng/mL (50 nmol/L) and above in the NASEM framework. Higher is not established as better: the 2024 Endocrine Society panel found no defined optimal level for disease prevention, and values above 50 ng/mL (125 nmol/L) are linked to potential adverse effects. We do not print an optimal number because the bodies that set these cutoffs say there is not one.

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02  /  Why it matters

What the number tells you

Vitamin D is required for calcium absorption and bone health; sustained deficiency causes rickets in children and osteomalacia in adults. The cutoffs below are the National Academies (NASEM) framework as stated by the NIH Office of Dietary Supplements. Worth knowing before you order a test: the Endocrine Society's 2024 guideline found no clinical-trial evidence to support routine 25(OH)D screening in the general population, found no clear evidence for an optimal target level, and suggests against routine testing in people without an established indication.

03  /  In practice

Testing and what moves it

When it is tested

  • With an established indication: bone disease, malabsorption, kidney or liver disease, or medicines that affect vitamin D metabolism.
  • The Endocrine Society (2024) suggests against routine testing in healthy adults, including in people with obesity or dark complexion, because trial evidence does not support it.
  • If you do test, the RDA context: 600 IU/day for adults 19 to 70 and 800 IU/day over 70 (NASEM).

What raises it

  • Sun exposure, vitamin D-containing food (fatty fish, fortified milk) and supplements.
  • Levels above 50 ng/mL usually come from high-dose supplementation, not sun.

What lowers it

  • Limited sun exposure, darker skin (more melanin means slower skin synthesis), malabsorption, obesity, kidney and liver disease.
  • Winter at higher latitudes.

04  /  Related

Read next

Hemoglobin A1C A1CFerritinTSH (thyroid-stimulating hormone) TSH

Frequently asked questions

What is a normal vitamin D level?

In the NASEM framework the NIH ODS states, 20 ng/mL (50 nmol/L) and above is adequate for bone and overall health; under 12 ng/mL is deficient; over 50 ng/mL is linked to potential adverse effects. Some labs and societies have used higher "sufficiency" bars, but the 2024 Endocrine Society guideline found no evidence defining an optimal target.

Should I get my vitamin D tested?

Probably not routinely. The Endocrine Society's 2024 guideline suggests against routine 25(OH)D testing in all populations it considered, because no trial evidence supports screening and there is no established target. Testing makes sense with a clinical indication such as bone disease or malabsorption.

My result is in nmol/L. How do I convert it?

Divide by 2.5: 50 nmol/L is 20 ng/mL, 125 nmol/L is 50 ng/mL. US labs usually report ng/mL; most other countries report nmol/L.