Vitamin D, specifically 25-hydroxyvitamin D (25-OH vitamin D), is vital for bone health, aiding in calcium and phosphorus absorption, and plays a role in reducing inflammation, cell growth modulation, and supporting immune and neuromuscular functions. It is essential for preventing rickets in children, osteomalacia in adults, and linked to reducing the risk of osteoporosis, cardiovascular diseases, certain cancers, autoimmune conditions, and depression. Vitamin D levels are influenced by dietary factors, sun exposure, and individual characteristics like age and skin pigmentation.
Deficiency in vitamin D can cause weak bones in children (rickets) and adults (osteomalacia), and contribute to osteoporosis. Low levels are also associated with increased risks of cardiovascular diseases, certain cancers, and impaired immune function. Factors such as limited sun exposure, dark skin, obesity, and conditions affecting fat absorption like celiac or Crohn's disease can reduce vitamin D levels. Additionally, magnesium deficiency can impair vitamin D activation, and liver or kidney diseases can affect its conversion to active forms.
Conversely, vitamin D toxicity, though rare, can result from excessive supplementation, leading to hypercalcemia with symptoms like nausea and kidney complications. Balanced vitamin D levels are typically achieved through diet, sunlight, and possibly supplementation. Obesity can sequester vitamin D in fat tissue, reducing its availability, while aging and darker skin reduce skin-based vitamin D production. Regular monitoring is advised for those at risk of deficiency or on high-dose supplements.
To maintain healthy Vitamin D levels:
Ensure regular, safe sun exposure. Aim for 10-30 minutes of midday sunlight several times per week, depending on your skin type and location.
Consume vitamin D-rich foods such as fatty fish (salmon, mackerel, sardines), egg yolks, and fortified dairy products or plant-based alternatives.
Consider vitamin D supplementation, especially if you have limited sun exposure, darker skin, or live in northern latitudes. Consult with a healthcare provider for appropriate dosage.
Maintain a healthy weight, as obesity can affect vitamin D absorption and utilization.
Ensure adequate intake of magnesium, which is necessary for vitamin D metabolism. Include magnesium-rich foods like nuts, seeds, and leafy greens in your diet.
Vitamin D (25-OH) can be measured in: ng/100mL, ng/dL, ng/L, ng/mL, ng%, nmol/L, µg/L
Reference ranges represent typical values for healthy individuals. Your healthcare provider must interpret your specific results.
| Age Range | Gender | Unit | Optimal | Normal | Source |
|---|---|---|---|---|---|
| All ages | All genders | ng/mL | - | 25 - 80 | Pagana, 2019 |
Vitamin D has anti-inflammatory properties and plays a role in modulating the immune system. Low levels of vitamin D are associated with increased susceptibility to infection, chronic inflammation, and autoimmunity. Adequate vitamin D levels can help reduce inflammation and support immune health.[Cannell, 2015][Calton, 2015]
Explore 6 additional health topics related to this biomarker in the Health3 app.
Vitamin D, as calcitriol (1,25(OH)2D), increases intestinal phosphate absorption and also facilitates its renal reabsorption, leading to elevated serum phosphate levels[Akimbekov, 2022][Shaker, 2000].
Explore 3 additional biomarker interactions related to this biomarker in the Health3 app.
The test you receive from a lab measures 25-hydroxyvitamin D (abbreviated 25(OH)D or calcidiol) — the major circulating form of vitamin D and the best indicator of overall vitamin D status. It is produced in the liver from both dietary vitamin D and vitamin D made in the skin by UVB sunlight. The active hormone form, calcitriol (1,25-dihydroxyvitamin D), is tightly regulated by the kidneys and parathyroid hormone and is not a reliable measure of nutritional status. When your doctor orders a "vitamin D test," they are almost always ordering the 25(OH)D version.
Results are reported in either ng/mL (used primarily in the US) or nmol/L (used in Europe, Canada, Australia, and the UK). To convert ng/mL to nmol/L, multiply by 2.5. For example: 30 ng/mL = 75 nmol/L; 50 ng/mL = 125 nmol/L. Always confirm which unit your lab uses before comparing to reference ranges. Our free blood test unit converter can assist with conversions.
Different organisations define vitamin D sufficiency differently. Understanding these thresholds helps you interpret your result in context. Note that individual laboratory ranges may vary, and your healthcare provider's interpretation matters most.
The 2024 Endocrine Society guideline update is significant: it no longer recommends supplementing healthy adults to targets above 20 ng/mL unless they have specific risk factors. For people over 75, those at high fracture risk, or pregnant women, the Society still supports supplementation. See our detailed comparison in the Vitamin D optimal levels guide. You can also interpret your result using our Vitamin D level interpreter.
Vitamin D toxicity (hypervitaminosis D) is rare and almost exclusively caused by excessive supplementation, not sun exposure — because the skin has a self-limiting mechanism for vitamin D synthesis. Toxicity primarily manifests through hypercalcaemia (elevated calcium), which can cause nausea, vomiting, weakness, frequent urination, and in severe cases kidney damage.
Vitamin D deficiency is very common globally. Research suggests that roughly 40% of US adults have levels below 20 ng/mL. Low vitamin D can result from limited sun exposure, dark skin pigmentation (reduces UVB absorption), obesity (vitamin D sequesters in adipose tissue), malabsorption conditions (celiac disease, Crohn's disease, gastric bypass surgery), chronic kidney or liver disease, or simply inadequate dietary intake.
Consequences of deficiency include:
The following associations are largely observational — low vitamin D frequently co-occurs with these conditions, but randomised trial evidence for supplementation benefits varies:
For context on metabolic conditions related to vitamin D, see the Metabolic Health topic page. If you're tracking vitamin D as part of deficiency management, see our use-case guide: blood test tracking for vitamin D deficiency.
A single vitamin D reading gives you a snapshot, but trends matter more than any individual value. Vitamin D levels change with seasons (typically lowest in late winter in northern latitudes), supplementation, and changes in sun exposure. If you start a supplement or change your dose, research suggests retesting after 8–12 weeks to assess the full response, as it takes this long for levels to reach a new steady state.
Health3 lets you track 25(OH)D readings over time to see seasonal patterns and monitor your response to interventions. Testing just once a year — ideally at the season when your levels are expected to be lowest — provides useful longitudinal data.
Vitamin D does not act in isolation. The following markers provide important context:
See the broader Bone Health and Energy & Fatigue topic pages for related biomarkers.
Most guidelines define sufficiency as ≥20 ng/mL (50 nmol/L). The 2011 Endocrine Society guideline suggested ≥30 ng/mL (75 nmol/L) for at-risk populations, but the 2024 update no longer supports supplementing all adults to higher targets. Your own lab's reference range and your healthcare provider's clinical context are the most relevant guides.
The IOM defines deficiency as <12 ng/mL (30 nmol/L) and insufficiency as 12–19 ng/mL. The Endocrine Society sets deficiency at <20 ng/mL. Below 10 ng/mL is considered severe deficiency and warrants prompt treatment. Values between 20–29 ng/mL are often described as "insufficient" in clinical practice, particularly for older adults, pregnant women, or those with osteoporosis.
20 ng/mL (50 nmol/L) is the minimum sufficient level per the IOM and NHS; most adults at this level have adequate vitamin D for bone health. 30 ng/mL (75 nmol/L) is the threshold preferred by the 2011 Endocrine Society guideline for populations with higher requirements. 50 ng/mL (125 nmol/L) is considered within the optimal range by many functional medicine practitioners, though RCT evidence for benefits above 30 ng/mL in healthy adults is limited. Use the Vitamin D level interpreter to evaluate your specific result in context.
For most adults, the RDA is 600–800 IU/day, with a tolerable upper limit of 4,000 IU/day. People with confirmed deficiency may be prescribed higher doses (e.g., 50,000 IU weekly) for a loading period under medical supervision. The 2024 Endocrine Society guideline recommends empirical supplementation at 600–800 IU for adults aged 50–74 with risk factors, and 800–1,000 IU for those aged 75+ — without needing baseline testing. Always consult a healthcare provider before starting high-dose supplementation.
Research suggests vitamin D3 (cholecalciferol) raises serum 25(OH)D more effectively and maintains levels longer than equivalent doses of vitamin D2 (ergocalciferol). Most clinical guidelines prefer D3. Vegans may prefer D2 or lichen-derived D3 supplements.
Very few foods contain significant vitamin D naturally: fatty fish (salmon, mackerel, sardines), egg yolks, and beef liver are the main sources. Many dairy products, plant milks, and cereals are fortified. In practice, diet alone rarely maintains sufficient levels without adequate sun exposure or supplementation, particularly in northern latitudes or for people with limited sun access.
Studies suggest an association between low vitamin D levels and poor sleep quality, shorter sleep duration, and daytime sleepiness. The proposed mechanism involves vitamin D receptors in brain regions involved in sleep regulation. However, RCT evidence for sleep improvement from supplementation is limited. Explore the Energy & Fatigue topic page for related markers.
Research suggests that adequate vitamin D supports muscle function, strength, and recovery — making it particularly relevant for athletes. Studies indicate that vitamin D deficiency is common even among elite athletes, especially those who train indoors. Many sports medicine practitioners recommend maintaining levels above 40 ng/mL for performance purposes, though the evidence base is still developing. See our use-case page on blood test tracking for athletes and bodybuilders.
This page is for educational purposes only and does not constitute medical advice, diagnosis, or treatment. Vitamin D reference ranges vary between laboratories. A result outside the published ranges does not necessarily indicate disease, and a result within range does not rule out a clinical issue. Always discuss your blood test results with a qualified healthcare provider who can interpret them in the context of your full clinical picture. Biomarker tracking in Health3 is designed for personal health awareness, not clinical diagnosis.
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