What this test measures
Most labs that report "Vitamin D3" or "Vitamin D" measure total 25-hydroxyvitamin D in serum (the sum of D2 and D3 forms). It reflects both diet and skin synthesis from sunlight, has a long half-life (about 3 weeks), and is the single best test of body vitamin D stores.
Vitamin D is fat-soluble; it is converted to 25-OH D in the liver and then to its active form 1,25-dihydroxyvitamin D (calcitriol) in the kidney. Calcitriol regulates calcium absorption, bone mineralisation, immune function and many other processes.
Why it matters
India has one of the highest prevalences of vitamin D deficiency in the world — multiple large studies report deficiency in 70–90% of urban adults, even in sunny regions. Causes include dark skin (reduced synthesis), conservative dress, indoor lifestyles, air pollution (reduces UV-B), low dietary intake, and predominantly vegetarian diets. Children, pregnant women, the elderly and people with darker skin are at highest risk.
Consequences range from bone disease (rickets in children, osteomalacia and osteoporosis in adults) to muscle pain and weakness, fatigue, depression, and an increased risk of falls and fractures. Treatment is cheap and effective — high-dose oral cholecalciferol followed by a maintenance dose. The Endocrine Society defines deficiency as <20 ng/mL, insufficiency 20–29 ng/mL, and sufficiency ≥30 ng/mL.
How to prepare
No fasting required. Tell your doctor about any vitamin D supplements or injections you have taken in the last 3 months — a recent megadose injection can give a misleadingly high level. Continue your normal diet and supplements unless your doctor advises otherwise.
Markers & reference ranges
Reference ranges below are typical adult values. Your lab's reported range may differ slightly based on the assay platform and patient demographics — always read your report against the range printed on it.
| Marker | Normal range | If low | If high |
|---|---|---|---|
| 25-Hydroxyvitamin D (ng/mL)[1][2] | Deficiency <20 · Insufficiency 20–29 · Sufficient 30–100 · Toxicity >150 | <20 ng/mL — deficient. Symptoms — bone pain (especially low back, hips, ribs), muscle weakness, fatigue, frequent infections, low mood. Persistent low values cause osteomalacia in adults and rickets in children. <12 ng/mL — severe deficiency, needs treatment doses. 20–29 ng/mL — insufficient — supplementation recommended in adults at risk. | >100 ng/mL — supraphysiological — usually recent supplementation, no immediate harm. >150 ng/mL — toxicity risk: hypercalcaemia (nausea, vomiting, weakness, confusion, kidney stones, kidney injury). Almost always from over-supplementation; very rarely from granulomatous disease (sarcoid, TB, lymphoma — where 1,25(OH)2D is the culprit and 25-OH D may be normal). |
25-OH Vitamin D — interpretation and action
| 25-OH D (ng/mL) | Status | Typical treatment |
|---|---|---|
| < 10 | Severe deficiency | Cholecalciferol 60,000 IU weekly × 8 weeks → re-test → maintenance 1000–2000 IU/day |
| 10 – 19 | Deficiency | Cholecalciferol 60,000 IU weekly × 6–8 weeks → maintenance |
| 20 – 29 | Insufficiency | Cholecalciferol 1000–2000 IU/day; recheck in 3 months |
| 30 – 60 | Sufficient | Maintenance dose if not getting sun + dietary sources |
| 60 – 100 | High-normal | No action; check supplementation history |
| > 150 | Toxicity risk | Stop supplements; check calcium; symptomatic treatment |
Frequently asked questions
How common is vitamin D deficiency in India?
Very common — Indian studies show 70–90% deficiency in urban adults across all ages, including children, pregnant women and the elderly. Even people who live in sunny regions are often deficient because of skin colour, clothing, indoor lifestyles and air pollution.
Do I need to fast?
No fasting is required. If you had a vitamin D injection recently, mention it — recent megadoses give misleadingly high values.
What is the difference between D2 and D3?
D2 (ergocalciferol) is plant-derived; D3 (cholecalciferol) is the form made by skin and found in animal foods. D3 is more effective at raising and maintaining 25-OH D levels and is the supplement of choice. Most modern assays measure total (D2 + D3) 25-OH D.
How much sun exposure do I need?
About 15–30 minutes of midday sun on arms and legs, 3 times a week, helps — but in Indian conditions (skin colour, pollution, indoor jobs), this is often insufficient and supplementation is recommended at risk.
My vitamin D is 14 ng/mL. How is it treated?
High-dose oral cholecalciferol (often 60,000 IU weekly for 6–8 weeks), followed by re-testing and a maintenance dose (typically 1000–2000 IU/day). Severe deficiency with bone pain or muscle weakness may need a more intensive course under medical guidance.
Is vitamin D injection better than tablets?
For most people, weekly oral cholecalciferol works just as well, is cheaper and avoids the long-tail effect of injections. Injections are useful for severe deficiency, malabsorption, or when adherence is a concern.
Can too much vitamin D cause harm?
Yes — sustained levels above 100–150 ng/mL can cause hypercalcaemia, nausea, kidney stones and kidney injury. Stick to recommended doses. Routine high-dose supplementation without testing is not advised.
How often should I get tested?
Once at baseline, then 3 months after treatment to confirm response. Annually for maintenance, especially in pregnancy, the elderly, dark-skinned individuals, and people on long-term steroids or anti-epileptics.
Related Vitamins / Nutrition tests
Tests commonly ordered alongside VITAMIN D3, or that help interpret an unexpected result.
Sources & references
- Endocrine Society — Vitamin D Clinical Practice Guideline · accessed 2026-05-30T00:00:00.000Z
- NIH Office of Dietary Supplements — Vitamin D · accessed 2026-05-30T00:00:00.000Z
- NCBI StatPearls — Vitamin D Deficiency · accessed 2026-05-30T00:00:00.000Z
- ICMR Recommended Dietary Allowances for Indians 2020 · accessed 2026-05-30T00:00:00.000Z
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