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Vitamin D
The vitamin of sunlight and bones: the test measures 25-hydroxyvitamin D, the storage form in the blood.
Other names: 25-hydroxyvitamin D, 25(OH)D, calcidiolSection: Vitamins
Updated: August 29, 2026·MedProtect editorial team Reference information — not a diagnosis or a prescription
In shortThere is no single agreed range: many experts recommend a level of 20–40 ng/mL (60–100 nmol/L), while others recommend 30–50 ng/mL (75–125 nmol/L). Reports describe the total 25(OH)D level as deficient, insufficient, sufficient, or possibly toxic.
Reference ranges
Group
Reference range
Many experts recommend
20–40 ng/mL (60–100 nmol/L)
Others recommend
30–50 ng/mL (75–125 nmol/L)
Expert groups recommend different ranges, and normal value ranges vary slightly among different laboratories. Reports usually describe the result in words: deficient, insufficient, sufficient, or toxic.
Reference range vs optimal — not the same thing
Many laboratories quote 30–100 ng/mL. Based on Endocrine Society guidance and meta-analyses, the optimal level for most adults is 40–60 ng/mL (100–150 nmol/L): below 20 is deficiency, 20–30 insufficiency. Sustained values above 100 carry a risk of toxicity.
Check your value
Enter the number from your lab report — see how it compares with the typical range. Mind the units shown in the chosen row.
A rough comparison with a typical range, not a diagnosis. Reference ranges vary between laboratories — check the range on your own report and let a clinician interpret the result.
What this marker is
A vitamin D test measures the level of vitamin D in the blood. Vitamin D helps the body absorb calcium to build healthy bones and teeth, and it keeps muscles, nerves, and the immune system working normally. A marked deficiency can lead to bone disorders and other medical conditions.
Vitamin D comes from three sources: sunlight on bare skin, certain foods — only a few, such as egg yolks, liver, and fatty fish, contain it naturally, which is why it is added to many cereals and dairy products — and supplements. Before the body can use vitamin D, the liver changes it into 25-hydroxyvitamin D, or 25(OH)D. Most vitamin D blood tests measure 25(OH)D because that is the most accurate way to see whether the body has enough. A different test measures “active vitamin D” (calcitriol); it is not used to check vitamin D status but may help monitor kidney problems or find the cause of abnormal calcium levels.
Results may be reported as total vitamin D or as the separate amounts of vitamin D2 (ergocalciferol, from fortified plant foods and ergocalciferol supplements) and vitamin D3 (cholecalciferol, made by the skin or absorbed from animal sources and cholecalciferol supplements). The two forms work similarly in the body; the important value is the total 25-hydroxyvitamin D level.
Routine vitamin D testing is not recommended for everyone, including pregnant women. Testing is done when a bone or other health condition could be caused by very low levels — osteomalacia, low bone density, osteoporosis, rickets in children — or when the risk of deficiency is high: little sunlight exposure, malnutrition, weight-loss surgery, conditions that impair nutrient absorption such as Crohn's disease, ulcerative colitis, or celiac disease, kidney or liver disease, age over 65, obesity, or medicines that affect vitamin D levels, such as certain statins, steroids, weight-loss medicines, or phenytoin. If supplements are being taken for a diagnosed deficiency, a repeat test shows whether the level is improving.
When it is high
Too much vitamin D from supplementsA higher-than-normal level — hypervitaminosis D — is most commonly caused by taking too much vitamin D. Getting too much from sunlight or food alone does not happen; supplements are the usual source.
HypercalcemiaExcess vitamin D can result in too much calcium in the blood, which may lead to many symptoms — nausea and vomiting, poor appetite, constipation, muscle weakness, weight loss — and to kidney damage.
When it is low
Too little sunlightLack of skin exposure to sunlight, darkly pigmented skin, or consistent use of high-SPF sunscreen reduce the skin's own production of vitamin D.
Diet and absorption problemsToo little vitamin D in the diet, poor food absorption, and poor vitamin D absorption due to advanced age, weight-loss surgery, or conditions in which fat is not absorbed well all lower the level.
Liver and kidney diseasesBoth organs take part in converting vitamin D into its usable forms, so their diseases lower the measured level.
Certain medicinesPhenytoin, phenobarbital, and rifampin are among the medicines that can lower vitamin D.
Groups at higher riskA low level is more common in African American children, especially in the winter, and in infants who are breastfed only, because breast milk is low in vitamin D.
What can skew the result
These factors can shift the value without any disease — worth considering before a retest:
Sunlight exposure, skin pigmentation, and sunscreen useCertain statins, steroids, weight-loss medicines, phenytoin, phenobarbital, rifampinKidney or liver diseaseConditions that impair nutrient absorption: Crohn's disease, ulcerative colitis, celiac diseaseAge over 65, obesity, weight-loss surgery
How to prepare
Usually no fasting is needed, but this depends on the laboratory and the testing method — the laboratory's instructions take precedence. The provider should know about all medicines, vitamins, and supplements being taken, because they may affect the results; nothing is stopped without the provider's advice.
When a retest makes sense
For a deficient or insufficient result, the provider may recommend vitamin D supplements and/or more vitamin D-rich foods — usually a safer strategy than more sun, which may cause skin cancer — and a repeat test shows whether the level is improving. For a high or toxic result, the supplements are stopped, because too much vitamin D can seriously damage organs and blood vessels.
Who usually reviews this result
A result outside the reference range is usually reviewed by: your GP or primary care doctor. Bring your lab report and any previous results to the appointment.
Names used on lab reports
Your report may use any of these names: 25-hydroxyvitamin D25(OH)DCalcidiolCholecalciferol testErgocalciferol test
Units and conversion
Measured in: ng/mL
ng/mL=nmol/L
ng/mL × 2.496 = nmol/L. Example: 30 ng/mL = 75 nmol/L. Results are rounded to 2 decimal places.
Several markers on your report?
See how MedProtect explains results in the app: the whole report, a check of the recognized values, and a clear breakdown.
No. Routine testing of all adults, even during pregnancy, is generally not recommended. The test is for people with a condition that could be caused by low vitamin D or with a high risk of deficiency.
What is the difference between D2, D3, and total vitamin D?
D2 (ergocalciferol) comes from fortified plant foods and ergocalciferol supplements; D3 (cholecalciferol) is made by the skin or absorbed from animal sources and cholecalciferol supplements. The two work similarly, and the number that matters is the total 25-hydroxyvitamin D level.
Can vitamin D be too high?
Yes, and supplements are almost always the cause. Too much vitamin D can raise blood calcium and damage the kidneys; symptoms include nausea, vomiting, poor appetite, constipation, muscle weakness, and weight loss.
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