Lab result explainedVitamins and mineralsLast updated November 1, 2026

Vitamin D levels (25-hydroxyvitamin D): what low, normal and high mean

Vitamin D (25-hydroxyvitamin D) (25(OH)D) · 25-hydroxyvitamin D · reported in ng/mL (multiply by 2.5 for nmol/L)

The vitamin D blood test measures 25-hydroxyvitamin D, the storage form of vitamin D made in the liver from what you get through skin sunlight exposure, food and supplements, and it is the number that shows whether you have enough. On US reports, 20 ng/mL or more is adequate for bone health, 12 to 19 ng/mL is insufficient, and below 12 ng/mL is deficient; many labs print a range of 30 to 100 ng/mL, which reflects a more generous target rather than a different science. The two most common reasons it is low are simply too little sun (winter, indoor life, darker skin, sunscreen) and carrying extra body fat, which holds vitamin D away from the blood.

Low vitamin D is common: roughly 4 in 10 US adults are below 20 ng/mL and about 1 in 20 below 12 ng/mL, with winter, northern latitude, darker skin and obesity all raising the odds. It rarely causes symptoms on its own at mild levels, which is why most results are found on screening. High vitamin D from sunlight is impossible, and toxicity comes only from supplements, typically tens of thousands of units a day for months, pushing 25-hydroxyvitamin D above 150 ng/mL and calcium with it.

This page explains what the test measures and why the thresholds differ, gives normal vitamin D levels by age (which, in short, do not change much), the causes and symptoms of low and high results, how long correction takes, and when a result needs more than a supplement.

25(OH)D at a glance

The test measures 25-hydroxyvitamin D (25(OH)D), the circulating storage form; it reflects sun, food and supplement intake over the past 2–3 months.
Adequate: 20 ng/mL (50 nmol/L) or more by NIH criteria; many labs and the Endocrine Society's older guideline use 30 ng/mL as the lower limit.
Deficient: under 12 ng/mL; insufficient: 12–19 ng/mL; the same cut-offs apply at every age from infancy to old age.
Low vitamin D: lack of sun, darker skin, obesity, malabsorption (celiac, bariatric surgery), kidney or liver disease, some medications.
Toxic: over 150 ng/mL with high blood calcium, almost always from supplements of 10,000 IU a day or more for months; the safe upper intake is 4,000 IU a day.
Next step: 1,000–2,000 IU of D3 daily for mild insufficiency, higher short courses for deficiency, and a recheck after about 3 months.

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What 25(OH)D measures

Vitamin D arrives in two ways: skin makes vitamin D3 when UVB light hits it, and the diet supplies D3 (fatty fish, eggs, fortified milk, most supplements) or D2 (mushrooms, some fortified foods and prescription capsules). The liver converts both into 25-hydroxyvitamin D, which circulates for 2 to 3 weeks and is the form the standard test measures. Because it is stable and reflects total input from all sources over the previous couple of months, 25(OH)D is the agreed measure of vitamin D status.

The active hormone, 1,25-dihydroxyvitamin D, is made by the kidneys from 25(OH)D in tightly controlled amounts and is not a useful test of vitamin D status: it stays normal, or even high, in deficiency because parathyroid hormone pushes its production up. It is measured only in specific situations such as kidney disease, sarcoidosis or unexplained high calcium.

Results are reported in ng/mL in the US and nmol/L elsewhere; multiply ng/mL by 2.5 to get nmol/L. Different assay methods disagree by up to 10–20 percent, so a result of 18 and a result of 22 from two labs may reflect the same status. Levels are lowest at the end of winter and highest in late summer.

Normal range for 25(OH)D

Reference ranges vary between labs and by age, sex and pregnancy. Use the range printed on your own report.

Group	Typical range (ng/mL (multiply by 2.5 for nmol/L))	Notes
Deficient (all ages)	Under 12 ng/mL (under 30 nmol/L)	Risk of rickets in children and osteomalacia in adults.
Insufficient (all ages)	12–19 ng/mL (30–49 nmol/L)	Inadequate for bone health in some people.
Adequate (all ages)	20 ng/mL (50 nmol/L) and above	NIH / National Academies threshold for bone health in 97.5% of people.
Common lab 'optimal' range	30–100 ng/mL	Based on the 2011 Endocrine Society guideline; the 2024 update no longer recommends targeting 30.
Infants and children	Same cut-offs as adults	Breastfed infants need 400 IU/day drops; deficiency under 12 ng/mL causes rickets.
Adults over 65 and pregnancy	Same cut-offs; aim for at least 20 ng/mL	Older skin makes less vitamin D and intake targets are higher (800 IU/day over 70).
Potentially toxic	Over 150 ng/mL (over 375 nmol/L)	With high calcium; levels of 100–150 are above target but rarely harmful alone.

High vitamin D (vitamin D toxicity)

A 25-hydroxyvitamin D level above the lab's upper limit (usually 100 ng/mL) means you are taking more vitamin D than you need, nearly always from supplements. Sunlight cannot cause toxicity because skin destroys excess pre-vitamin D, and diet cannot supply enough. Levels between 100 and 150 ng/mL are above target but rarely cause harm on their own; the supplement dose is reduced or paused and the level rechecked in a few months.

True vitamin D toxicity (hypervitaminosis D) is defined by a 25(OH)D above about 150 ng/mL together with a high blood calcium. The excess vitamin D drives the gut to absorb far more calcium than usual and pulls calcium from bone. High calcium is what causes the symptoms and the damage: nausea, vomiting, constipation, thirst, frequent urination, confusion, kidney stones and, if prolonged, kidney failure and calcium deposits in blood vessels. It typically takes daily doses of 10,000 IU or more, or a manufacturing or dosing error (for example, taking a weekly 50,000 IU capsule every day), for months.

A high result without high calcium is a warning to review the dose, not an emergency. A high result with high calcium needs the supplement stopped and prompt medical care; recovery takes weeks to months because vitamin D is stored in fat.

Common causes

High-dose supplements
Daily intakes above 10,000 IU for several months, or much higher single doses, overwhelm the body's storage and conversion controls. Online 'megadose' regimens and combined products (multiple supplements each containing vitamin D) are the usual route.
Dosing errors with prescription vitamin D
Taking a 50,000 IU weekly or monthly capsule daily, or pharmacy and labelling mistakes in liquid drops for infants, are well-documented causes of toxicity.
Manufacturing errors
Over-the-counter supplements are not tightly regulated; batches containing hundreds of times the labelled dose have caused clusters of toxicity. Third-party tested products reduce the risk.
Granulomatous diseases (sarcoidosis, tuberculosis) and some lymphomas
Immune cells in granulomas convert 25(OH)D to the active hormone without the kidney's controls, so even modest vitamin D intake can raise calcium. The 25(OH)D level itself may be normal; it is the 1,25 form and calcium that rise.
Excess vitamin D in animal feed or fortified foods (rare)
Historical outbreaks came from over-fortified milk; this is now very rare in the US but has occurred.
Lab artefact: recent large dose
A very large single dose (e.g. 100,000 IU) can push 25(OH)D above 100 ng/mL for a few weeks without toxicity; timing of the last dose matters when interpreting a high result.

Symptoms that can go with it

Often none below about 150 ng/mL
Nausea, vomiting, loss of appetite
Constipation
Excessive thirst and frequent urination
Fatigue, muscle weakness
Confusion, irritability, drowsiness
Bone pain
Kidney stones or flank pain
Irregular heartbeat (severe hypercalcemia)

Low vitamin D (deficiency and insufficiency)

A 25-hydroxyvitamin D below 20 ng/mL means your body is getting less vitamin D than it needs for calcium absorption and bone health; below 12 ng/mL is frank deficiency, where parathyroid hormone rises, calcium is pulled from bone, and over months to years adults develop osteomalacia (soft, painful bones and muscle weakness) and children develop rickets. Most low results are between 12 and 20 ng/mL and have no symptoms at all; they are found on screening in people with limited sun, darker skin or higher body weight, especially in late winter.

What a low level means for health beyond bones is less settled than headlines suggest. Observational studies link low vitamin D to almost every chronic disease, but the large randomized trials that gave vitamin D to people who were not deficient (VITAL, D-Health, ViDA) found no reduction in cancer, cardiovascular events, fractures or depression. The 2024 Endocrine Society guideline therefore recommends against routine testing in healthy adults under 75 and against chasing a specific target, while still advising supplementation for people at risk, in pregnancy, over 75 and in children.

Correcting a low level is straightforward and safe at ordinary doses. A level between 12 and 20 usually responds to 1,000–2,000 IU of D3 daily; a level under 12 is often treated with 50,000 IU weekly for 6–8 weeks or 5,000–6,000 IU daily, then a maintenance dose. Each 1,000 IU a day raises 25(OH)D by roughly 6–10 ng/mL after 2–3 months, less in people with obesity.

Common causes

Too little UVB sunlight
Skin makes most of the body's vitamin D, but UVB is absent in winter above about 37° latitude (roughly north of Atlanta or Los Angeles), is blocked by glass, clothing, cloud and sunscreen, and is weak before 10 am and after 3 pm. Indoor work and shift work are major contributors.
Darker skin
Melanin absorbs UVB, so darker skin needs 3–6 times longer sun exposure to make the same vitamin D. About 60–80% of Black adults in the US have 25(OH)D under 20 ng/mL, though bone outcomes do not track the number as closely, and some of the difference reflects assay and binding-protein factors.
Obesity
Vitamin D is fat-soluble and is diluted across a larger volume of body fat, so people with a BMI over 30 have 25(OH)D levels about a third lower for the same intake and need roughly 2–3 times the dose to correct a deficiency.
Older age
Skin over 65 makes about a quarter of the vitamin D that young skin does from the same sun, and older adults spend less time outdoors. Recommended intake rises to 800 IU daily over age 70.
Malabsorption
Celiac disease, Crohn's disease, cystic fibrosis, pancreatic insufficiency, cholestatic liver disease and gastric bypass or sleeve surgery all reduce absorption of fat-soluble vitamins. Deficiency after bariatric surgery is near universal without supplements.
Medications
Anticonvulsants (phenytoin, carbamazepine, phenobarbital), rifampin, some HIV drugs and long-term glucocorticoids speed vitamin D breakdown; orlistat and bile acid binders (cholestyramine) block its absorption.
Chronic kidney disease and liver disease
The liver makes 25(OH)D and the kidney makes the active hormone; advanced disease of either lowers levels and, in kidney disease, impairs activation so that 25(OH)D alone understates the problem.
Exclusive breastfeeding without drops
Breast milk contains very little vitamin D; infants who are not given 400 IU daily drops, especially darker-skinned infants or those born in winter, are at risk of rickets.
Low dietary intake
Few foods contain much vitamin D (fatty fish, egg yolks, fortified milk, cereals and plant milks, UV-exposed mushrooms). Vegan diets and dairy avoidance remove the main fortified sources.
Season and timing of the test
Levels are 5–10 ng/mL lower in late winter than late summer. A borderline result in March often reads normal in September without any change in habits.

Symptoms that can go with it

Usually none at mild levels
Fatigue
Bone or back pain, often diffuse and aching
Muscle weakness, aches or cramps, difficulty rising from a chair
Low mood
Frequent infections
Falls and fractures in older adults
Bowed legs, delayed growth or soft skull bones in infants and children (rickets)

Read it alongside

Calcium — low or low-normal with very low vitamin D; high calcium with high vitamin D defines toxicity; high calcium with normal vitamin D points to parathyroid disease.
Parathyroid hormone (PTH) — rises as vitamin D falls below about 20 ng/mL; a normal PTH suggests a borderline level is not biologically important.
Phosphate and alkaline phosphatase — low phosphate and high alkaline phosphatase accompany osteomalacia and rickets.
Creatinine and eGFR — kidney disease changes how vitamin D is activated and how it should be replaced.
Magnesium — magnesium is needed to activate vitamin D; deficiency blunts the response to supplements.
Bone density (DEXA) — in older adults, fracture risk, not the vitamin D number, drives treatment decisions.
Celiac antibodies — unexplained deficiency that does not correct with supplements prompts a check for malabsorption.

What usually happens next

For a level of 12–20 ng/mL without symptoms: start 1,000–2,000 IU of vitamin D3 daily with a meal, add fatty fish and fortified foods, and recheck in about 3 months if there is a reason to (bone disease, malabsorption, pregnancy); otherwise many clinicians do not retest.
For a level under 12 ng/mL: expect a loading course (for example 50,000 IU weekly for 6–8 weeks or 5,000–6,000 IU daily), calcium, phosphate and PTH tests, and a recheck at 3 months; symptoms of bone pain or weakness prompt X-rays or a bone scan.
For a level over 100 ng/mL: stop or cut the supplement, list every product that contains vitamin D, and have calcium checked; over 150 ng/mL or any high calcium needs same-week review.
Ask what the result was in ng/mL and which threshold your clinician is using (20 or 30); it changes whether you are 'low' at all.
If the level does not rise after 3 months of a reliable dose, ask about absorption (celiac disease, pancreatic or liver disease), medications and whether the product is third-party tested.

Diet, lifestyle and natural levers with evidence

What can move 25(OH)D once the cause is known. Nothing here replaces finding the cause.

Sensible sun exposure

Strong evidence

Skin exposure of arms and legs to midday sun for about 10–30 minutes, two to three times a week in spring and summer, produces the equivalent of 1,000–3,000 IU in light-skinned adults and raises 25(OH)D by 10–20 ng/mL over a season; darker skin needs several times longer. Below about 37° latitude this works most of the year; further north it does nothing from November to February.

Burning raises skin cancer risk and adds no extra vitamin D; stop before the skin reddens, and sunscreen after that is fine.

Vitamin D3 (cholecalciferol) supplements

Strong evidence

Daily D3 reliably raises 25(OH)D: roughly 6–10 ng/mL per 1,000 IU per day after 8–12 weeks, with smaller gains at higher starting levels and in obesity. A meta-analysis of randomized trials found D3 raises and maintains 25(OH)D better than D2, and daily dosing works at least as well as weekly or monthly. The tolerable upper intake is 4,000 IU daily for adults; 1,000–2,000 IU covers most people.

Doses above 4,000 IU daily should be short, prescribed and monitored. Check calcium if you also take calcium supplements or have kidney stones, sarcoidosis or parathyroid disease.

Taking vitamin D with the largest meal of the day

Moderate evidence

Vitamin D is fat-soluble. In a randomized trial, taking the same supplement with a meal containing about 30 g of fat increased 25(OH)D by around 30% more over 12 weeks than taking it with a fat-free meal, and an earlier study found switching to the largest meal of the day raised levels by about 50% in people who had been poor responders.

Fatty fish, fortified foods and UV-exposed mushrooms

Moderate evidence

A 3.5 oz serving of salmon provides 400–600 IU (wild more than farmed), sardines and mackerel 200–300 IU, a cup of fortified milk or plant milk about 100 IU, and UV-treated mushrooms up to 400 IU per serving. Feeding trials show two servings of fatty fish a week raise 25(OH)D by about 3–5 ng/mL; diet alone rarely corrects deficiency but keeps a corrected level stable.

Magnesium repletion

Preliminary evidence

The enzymes that activate vitamin D need magnesium. In a randomized trial of 180 adults, magnesium supplementation raised 25(OH)D in people whose baseline was low (under 30 ng/mL) and lowered it in those who started high, suggesting it helps normalize vitamin D metabolism. Magnesium-rich foods (nuts, seeds, legumes, whole grains, leafy greens) are a reasonable first step.

Weight loss

Preliminary evidence

Body fat holds vitamin D away from the blood. In weight-loss trials, losing 5–10% of body weight raised 25(OH)D by about 2–3 ng/mL without any change in intake, and larger losses after bariatric surgery raise it more (while malabsorption then lowers it). Weight loss improves response to a given supplement dose rather than replacing one.

When to see a clinician promptly

A vitamin D level over 150 ng/mL, or over 100 ng/mL with nausea, vomiting, thirst, frequent urination, confusion or constipation (possible high calcium).
A level under 12 ng/mL with bone pain, muscle weakness, difficulty walking, or a recent fracture from a minor fall.
Low vitamin D in an infant or child, especially with bowed legs, delayed walking or seizures (rickets and low calcium).
Low vitamin D that fails to rise after 3 months of a reliable dose, which suggests malabsorption or a medication effect.
Low vitamin D with chronic kidney disease, high calcium, a parathyroid condition or sarcoidosis, where standard dosing may not be safe.
Pregnancy with a level under 20 ng/mL.

Frequently asked questions

What are normal vitamin D levels by age?

The thresholds are the same at every age: under 12 ng/mL is deficient, 12–19 is insufficient and 20 or more is adequate, with many labs printing 30–100 as 'optimal'. What changes with age is how hard it is to reach them: older skin makes less vitamin D, so intake targets rise from 600 IU a day in adults to 800 IU over age 70, and infants need 400 IU drops from birth.

Is a vitamin D level of 25 low?

By the NIH and National Academies definition, 25 ng/mL is adequate for bone health. By the older Endocrine Society target of 30, it is mildly insufficient. In practice, 25 is a reasonable level for a healthy adult; if you have osteoporosis, malabsorption or are pregnant, your clinician may aim higher with a modest daily dose.

What level of vitamin D is dangerously low?

Below 12 ng/mL is deficient and, if prolonged, causes bone softening (osteomalacia) in adults and rickets in children. Levels under 5–8 ng/mL often come with low calcium and phosphate and real symptoms: bone pain, weakness and in children seizures. Even very low levels are corrected safely with a loading course of vitamin D3 over 6–8 weeks.

What vitamin D level is toxic?

Toxicity is defined by a 25-hydroxyvitamin D over about 150 ng/mL together with high blood calcium. It takes sustained supplement doses of 10,000 IU a day or more, or dosing errors, to get there; sun and food cannot. Levels of 100–150 ng/mL are above target and mean the dose should be cut, but rarely cause harm by themselves.

How much vitamin D should I take to raise my level?

Each 1,000 IU of D3 daily raises 25(OH)D by roughly 6–10 ng/mL after 2–3 months. For a level of 12–20, 1,000–2,000 IU daily is usually enough; for under 12, clinicians often prescribe 50,000 IU weekly for 6–8 weeks or 5,000–6,000 IU daily, then 1,000–2,000 IU to maintain. People with obesity or malabsorption need about double. Do not stay above 4,000 IU daily long term without monitoring.

Does low vitamin D cause fatigue, depression or hair loss?

Low vitamin D is associated with all three in observational studies, but randomized trials in people who were not deficient show no benefit from supplements for depression or fatigue. In true deficiency (under 12 ng/mL) correcting it can improve tiredness, muscle aches and bone pain. Hair loss evidence is weak; vitamin D is checked mainly to exclude a contributing deficiency.

Do I need a vitamin D blood test?

Not routinely if you are a healthy adult under 75; the 2024 Endocrine Society guideline advises against screening and in favor of a sensible daily intake instead. Testing is useful if you have osteoporosis or fractures, malabsorption, kidney or liver disease, take medications that affect vitamin D, have symptoms of deficiency, or take high doses and need a safety check.

D2 or D3, and does it matter when I take it?

D3 (cholecalciferol) raises and holds 25(OH)D more effectively than D2 (ergocalciferol) at the same dose, so D3 is preferred for over-the-counter use, though prescription D2 50,000 IU capsules work fine for loading. Take it with a meal containing some fat; time of day does not matter, and daily dosing is at least as effective as weekly.

References

Vitamin D: Fact Sheet for Health Professionals. NIH Office of Dietary Supplements (2024)View source
Vitamin D Test. MedlinePlus, National Library of Medicine (2023)View source
Vitamin D. Mayo Clinic (2023)View source
Demay MB, Pittas AG, Bikle DD, et al.. Vitamin D for the Prevention of Disease: An Endocrine Society Clinical Practice Guideline. Journal of Clinical Endocrinology and Metabolism (2024)View source
Holick MF, Binkley NC, Bischoff-Ferrari HA, et al.. Evaluation, treatment, and prevention of vitamin D deficiency: an Endocrine Society clinical practice guideline. Journal of Clinical Endocrinology and Metabolism (2011)View source
Holick MF. Vitamin D deficiency. New England Journal of Medicine (2007)View source
Manson JE, Cook NR, Lee IM, et al.. Vitamin D supplements and prevention of cancer and cardiovascular disease (VITAL). New England Journal of Medicine (2019)View source
Tripkovic L, Lambert H, Hart K, et al.. Comparison of vitamin D2 and vitamin D3 supplementation in raising serum 25-hydroxyvitamin D status: a systematic review and meta-analysis. American Journal of Clinical Nutrition (2012)View source
Kennel KA, Drake MT, Hurley DL. Vitamin D Deficiency in Adults: When to Test and How to Treat. Mayo Clinic Proceedings (2010)
Dai Q, Zhu X, Manson JE, et al.. Magnesium status and supplementation influence vitamin D status and metabolism: results from a randomized trial. American Journal of Clinical Nutrition (2018)View source
Dietary Reference Intakes for Calcium and Vitamin D. Institute of Medicine (National Academies Press); NCBI Bookshelf (2011)View source

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This page is educational and is not medical advice or a diagnosis. Lab results have to be interpreted together with your history, symptoms and other results by a clinician who knows you. Do not start or stop a supplement to change a lab value before the cause is known.