Vitamin D (25-Hydroxyvitamin D)
A blood test that measures the level of vitamin D in the body, important for bone health, immune function, and calcium absorption.
Last medically reviewed: April 10, 2026 | Reviewed by LabResult.MD Editorial Team
What is Vitamin D?
Vitamin D is a fat-soluble vitamin that plays a critical role in helping the body absorb calcium and phosphorus, which are essential for building and maintaining strong bones. It also supports immune system function, muscle health, and brain cell activity.
The body produces vitamin D when the skin is exposed to sunlight. It can also be obtained from certain foods (like fatty fish, fortified milk, and egg yolks) and supplements. The 25-hydroxyvitamin D blood test is the most accurate way to measure how much vitamin D is in the body.
Why Is It Tested?
A healthcare provider may order a vitamin D test to:
- Check for vitamin D deficiency or insufficiency
- Monitor bone health, especially in older adults
- Evaluate calcium metabolism disorders
- Assess risk factors for osteoporosis or bone fractures
- Monitor people with conditions that affect vitamin D absorption (such as Crohn's disease or celiac disease)
- Evaluate fatigue, muscle weakness, or bone pain that could be related to low vitamin D
Normal Reference Ranges
Reference ranges may vary by laboratory, testing method, age, and other factors. Always use the ranges provided on your lab report.
| Status | Level (ng/mL) | Level (nmol/L) |
|---|---|---|
| Deficient | Less than 20 ng/mL | Less than 50 nmol/L |
| Insufficient | 20 – 29 ng/mL | 50 – 72 nmol/L |
| Sufficient (Normal) | 30 – 100 ng/mL | 75 – 250 nmol/L |
| Potentially Toxic | Greater than 100 ng/mL | Greater than 250 nmol/L |
What Does a High Vitamin D Level Mean?
Vitamin D levels above the normal range are uncommon but can occur, usually from taking too many vitamin D supplements. High levels could indicate:
- Excessive supplementation of vitamin D
- Granulomatous diseases (such as sarcoidosis), which can cause the body to produce excess vitamin D
- Certain lymphomas
Very high levels of vitamin D (toxicity) can lead to a buildup of calcium in the blood, which may cause nausea, weakness, kidney problems, and other symptoms. A healthcare provider may recommend adjusting supplement intake or further testing.
What Does a Low Vitamin D Level Mean?
Low vitamin D is very common, especially in people who live in northern latitudes, spend most of their time indoors, or have darker skin. Low levels could be related to:
- Insufficient sun exposure
- Inadequate dietary intake of vitamin D
- Conditions that reduce absorption (celiac disease, Crohn's disease, gastric bypass surgery)
- Liver or kidney disorders that affect vitamin D conversion
- Certain medications (such as some anti-seizure drugs and steroids)
- Obesity (vitamin D can become sequestered in fat tissue)
Over time, low vitamin D may contribute to weakened bones (osteomalacia in adults, rickets in children), increased fracture risk, muscle weakness, fatigue, and impaired immune function.
Common Next Steps
Depending on the result, a healthcare provider may recommend:
- Vitamin D supplementation (with dosage based on the severity of deficiency)
- Increased sun exposure and dietary changes
- Follow-up testing after 2–3 months to check if levels have improved
- Additional tests such as calcium, phosphorus, parathyroid hormone (PTH), or bone density scans
- Evaluation for underlying conditions if deficiency persists despite supplementation
Frequently Asked Questions
What is a normal vitamin D level?
A sufficient vitamin D level is generally considered to be 30–100 ng/mL (75–250 nmol/L). Levels between 20–29 ng/mL are considered insufficient, and levels below 20 ng/mL indicate deficiency, according to the Endocrine Society.
How common is vitamin D deficiency?
Vitamin D deficiency is very common. According to research published in the journal Nutrition Research, an estimated 42% of U.S. adults are vitamin D deficient. Risk factors include limited sun exposure, darker skin pigmentation, obesity, living in northern latitudes, and being over age 65.
What is the difference between vitamin D2 and D3?
Vitamin D2 (ergocalciferol) comes from plant sources and fortified foods, while vitamin D3 (cholecalciferol) is produced by the skin in response to sunlight and found in animal-based foods. Research suggests vitamin D3 is more effective at raising and maintaining blood levels. The 25-hydroxyvitamin D blood test measures the combined total of both forms.
Related Tests and Biomarkers
Sources
- Endocrine Society. Evaluation, Treatment, and Prevention of Vitamin D Deficiency (Clinical Practice Guideline)
- Forrest KYZ, Stuhldreher WL. Prevalence and correlates of vitamin D deficiency in US adults. Nutrition Research. 2011;31(1):48-54
- MedlinePlus. Vitamin D Test. U.S. National Library of Medicine
Disclaimer: This information is for educational purposes only and is not a substitute for professional medical advice. Reference ranges vary by laboratory. Always discuss your results with a qualified healthcare provider.