Vitamin D: D2 vs D3, Sources, Deficiency, Evidence and Excess
Vitamin D explained: sunlight, food and supplement sources, official US, UK and EU intake levels and upper limits, what large trials found, deficiency, and the risks of too much.
Content last updated . This page has not been medically reviewed.
What is Vitamin D good for?
What the body uses it for, and how strong the evidence is. A normal job in the body is not proof that extra supplements add benefit; each card says which.
Calcium and phosphate regulation
Established roleVitamin D helps the body regulate calcium and phosphate.
Supplements: Supplements correct a shortfall; extra intake above need has not been shown here to add bone benefit.
Bone formation
Deficiency linkVitamin D helps the body absorb calcium, which is needed for normal bone formation.
Supplements: Supplements treat or prevent deficiency-related bone disease; benefit for bones in people with adequate levels is not established from sources read.
Teeth health
Established roleCalcium and phosphate balance that vitamin D helps regulate also supports teeth.
Supplements: Relevant mainly when vitamin D is low.
Muscle function
Deficiency linkVitamin D helps regulate calcium and phosphate that muscles need; severe deficiency can cause muscle weakness.
Supplements: Supplements help when weakness comes from deficiency; no verified benefit otherwise from sources read.
Making vitamin D from sunlight
Established roleSkin makes vitamin D when exposed to sunlight, so season, skin tone, clothing and location change how much you make.
Supplements: Sunlight cannot cause vitamin D overdose, but sun exposure raises skin cancer risk.
Preventing rickets and osteomalacia
Deficiency linkTaking vitamin D (with enough calcium) helps prevent and treat these bone diseases.
Supplements: Applies to people at risk of low vitamin D.
Connected topics
Open a group to see how each topic connects and how strong the evidence is.
Health goals (1)
- Bone HealthEstablished role
Vitamin D helps the body absorb calcium and regulate calcium and phosphate for bones. Extra supplements mainly matter for people who are low in vitamin D.
Body systems (11)
- Bones, Joints & MusclesEstablished role
Vitamin D helps regulate calcium and phosphate, which bones, teeth and muscles need.
- Integumentary SystemEstablished role
The skin makes vitamin D when exposed to sunlight, so sunlight, season, skin tone and clothing change how much you make.
- Musculoskeletal SystemEstablished role
Vitamin D helps regulate calcium and phosphate, which bones and muscles need. Severe lack causes soft bones.
- Digestive SystemDeficiency link
Gut disorders that reduce absorption, such as Crohn's disease, ulcerative colitis and celiac disease, can lower vitamin D levels.
- Kidney & UrinaryDocumented risk
The kidneys help turn vitamin D into its usable form. Too much vitamin D, almost always from supplements, can raise blood calcium and cause kidney damage and kidney stones.
- Urinary SystemDocumented risk
The kidneys help turn vitamin D into its usable form. Too much vitamin D can raise blood calcium and cause kidney damage and kidney stones.
- Cardiovascular SystemDocumented risk
Very high vitamin D intake can raise blood calcium and lead to calcium deposits in the heart. This is a risk of excess, not a heart benefit.
- Gut HealthDeficiency link
Poor absorption in gut disorders can lower vitamin D levels. This is about gut disease affecting vitamin D, not vitamin D treating the gut.
- Heart & CirculationDocumented risk
Very high vitamin D intake can raise blood calcium and lead to calcium deposits in soft tissues such as the heart. This is a risk of excess, not a heart benefit.
- Hepatic / Liver SystemEstablished role
The liver is part of how the body turns vitamin D into a usable form, so liver disease can affect vitamin D status.
- Liver & DetoxEstablished role
Liver disease can impair conversion of vitamin D to its usable form. Vitamin D is not a liver treatment.
Body parts (8)
- BonesEstablished role
Vitamin D helps the body absorb calcium for normal bone formation. Deficiency can cause rickets in children and osteomalacia in adults.
- SkinEstablished role
Skin makes vitamin D from sunlight. Sun exposure also carries a skin cancer risk, so it is not a free source.
- GutDeficiency link
The gut absorbs vitamin D from food and supplements; malabsorption disorders can lower levels.
- KidneysDocumented risk
The kidneys help activate vitamin D; kidney disease can impair this. Excess vitamin D can damage the kidneys and cause kidney stones.
- MusclesEstablished role
Vitamin D helps regulate calcium and phosphate that muscles need; severe deficiency can bring muscle weakness.
- HeartDocumented risk
Excess vitamin D can cause calcium deposits in soft tissues such as the heart.
- LiverEstablished role
The liver helps convert vitamin D to a usable form, so liver disease can affect vitamin D status.
- LungsDocumented risk
Excess vitamin D can cause calcium deposits in soft tissues such as the lungs.
Root causes (6)
- Lack of SunlightDeficiency link
Little sun exposure, cloudy or shaded conditions, covering skin, and dark skin all reduce the vitamin D the skin makes.
- Nutrient DeficiencyDeficiency link
Not getting enough vitamin D leads to rickets in children and osteomalacia (soft, painful bones) in adults.
- Digestive DysfunctionDeficiency link
Malabsorption disorders such as Crohn's disease, ulcerative colitis and celiac disease reduce vitamin D absorption.
- Medication Side EffectsDocumented risk
Some statins, steroids and weight-loss medicines can affect vitamin D levels. Never stop a prescribed medicine on your own.
- AgingDeficiency link
NHS advice lists people over 65 as a group to take a vitamin D supplement to help prevent rickets and osteomalacia.
- Poor DietDeficiency link
Poor food intake or malnutrition raises the chance of low vitamin D, since few foods contain much of it.
Habits (2)
- Sunlight ExposureDeficiency link
Sunlight on bare skin lets the body make vitamin D. NHS says about 15 minutes without sunscreen, 2 or 3 times a week from late March to September, can help; sun also raises skin cancer risk.
- Balanced NutritionDeficiency link
Few foods contain much vitamin D (fatty fish, egg yolks, liver, fortified foods), so diet alone often falls short in low-sun seasons.
Biomarkers (1)
- Vitamin DEstablished role
Vitamin D status is checked with the 25-hydroxyvitamin D blood test. Ranges differ between sources and labs, and a clinician interprets the result.
Conditions & symptoms (7)
- HypercalcemiaDocumented risk
Too much vitamin D, almost always from supplements, can raise blood calcium. Symptoms include nausea, vomiting, constipation, weakness and confusion.
- OsteomalaciaDeficiency link
Lack of vitamin D or calcium causes osteomalacia in adults, with bone pain and soft bones.
- RicketsDeficiency link
Lack of vitamin D (or calcium) causes rickets in children, with soft bones and bowed legs. Treatment includes vitamin D and calcium, chosen by a doctor.
- Vitamin D DeficiencyDeficiency link
Low vitamin D can weaken bones; blood levels below about 30 to 50 nmol/L are described as too low for bone health, and ranges vary by lab.
- HypervitaminosisDocumented risk
Vitamin D toxicity is the effect of taking far too much, nearly always from supplements, and cannot happen from sunlight.
- NephrolithiasisDocumented risk
MedlinePlus lists kidney stones and kidney damage among the effects of too much vitamin D.
- OsteoporosisDeficiency link
MedlinePlus says deficiency can weaken bones, causing osteoporosis in adults. This is not the same as saying supplements prevent osteoporosis in people who are not deficient.
Overview
Vitamin D is a fat-soluble vitamin that helps the body regulate calcium and phosphate, which bones, teeth and muscles need. [1] It is unusual because skin makes it when exposed to sunlight, so what you need from food and supplements depends on where you live, the season, your skin and how much time you spend outdoors. [1][2]Forms and where it comes from
- Sunlight. The NHS (UK) says that from about late March or early April to the end of September most people can make the vitamin D they need from sunlight, but not between October and early March. [1] MedlinePlus adds that cloudy days, shade and dark-colored skin cut production, and that sun exposure is a skin cancer risk. [2] The full picture is on Vitamin D and sunlight.
- Food. Few foods contain much: oily fish, red meat, egg yolks, liver and fortified foods in the UK. [1] MedlinePlus adds beef liver, cheese, mushrooms exposed to ultraviolet light and fortified milk, with most US milk fortified at 400 IU per quart. [2] UK cows' milk is generally not fortified. [1] The NHS says to avoid liver if you are pregnant. [1]
- Supplements come as D2 (ergocalciferol) and D3 (cholecalciferol). [2] MedlinePlus says the two work similarly in the body. [3] The head-to-head question is on Vitamin D2 vs D3.
Who may need assessment
The NHS advises a daily supplement all year for people who are not often outdoors (for example frail or housebound), live in care homes, usually cover most skin outdoors, or have dark skin, and for all babies who are breastfed or have under 500 ml of formula a day, and children 1 to 4. [1] MedlinePlus lists age over 65, obesity or weight-loss surgery, osteoporosis, limited sun exposure, certain medicines and poor gut absorption as reasons a clinician may test. [3] See Vitamin D deficiency and testing and Vitamin D and K for newborns.Deficiency
Lack of vitamin D can lead to rickets in children and osteomalacia (bone pain, soft bones) in adults. [1] [4] Do not diagnose deficiency from symptoms, and do not treat suspected deficiency alone: a doctor checks vitamin D and calcium levels and chooses treatment. [4]Official intake levels
Amounts come in micrograms (mcg) and International Units (IU); 1 mcg is 40 IU. [1] These are references for stated groups, not personal advice. See RDA, AI, DV and UL.| Source and year | Population | Amount per day |
|---|---|---|
| NHS (UK), reviewed 2020 | Children 1 year and older and adults, including pregnancy and breastfeeding | 10 mcg (400 IU) [1] |
| NHS (UK) | Babies up to 1 year | 8.5 to 10 mcg [1] |
| US DRIs via MedlinePlus (reviewed 2025) | Infants 0 to 12 months (AI) | 400 IU (10 mcg) [2] |
| Same | Ages 1 to 70, pregnancy and breastfeeding (RDA); over 70 | 600 IU (15 mcg); 800 IU (20 mcg) [2] |
| Daily Value on US labels (FDA) | Label reference, not a requirement | 20 mcg [5] |
Upper limits (the most expected not to cause harm over time, not targets):
| Source and year | Population | Amount per day |
|---|---|---|
| NHS (UK) | Adults, pregnancy, breastfeeding, older adults, ages 11 to 17 | 100 mcg (4,000 IU) [1] |
| NHS (UK) | Ages 1 to 10; infants under 12 months | 50 mcg (2,000 IU); 25 mcg (1,000 IU) [1] |
| US via MedlinePlus (2025) | Ages 9 and older; ages 4 to 8; 1 to 3 years | 4,000 IU (100 mcg); 3,000 IU (75 mcg); 2,500 IU (63 mcg) [2] |
| US via MedlinePlus | Infants 0 to 6 months; 7 to 12 months | 1,000 IU (25 mcg); 1,500 IU (38 mcg) [2] |
| EFSA (EU), overview August 2025 | Ages 11 and older, including pregnancy and lactation | 100 mcg [6] |
| Same | Ages 1 to 10; infants 0 to 6 and 7 to 11 months | 50 mcg; 25 and 35 mcg [6] |
The NIH Office of Dietary Supplements page could not be read this session, so it is not cited. EFSA counts 1 mcg of D2 or D3 as 40 IU. [6]
What the evidence shows for specific uses
| Question | What the source found | Label |
|---|---|---|
| Rickets and osteomalacia | Caused by lack of vitamin D; treatment includes vitamin D and calcium [4] | Established |
| Fractures in generally healthy adults | VITAL: 25,871 US adults (men 50+, women 55+), 2,000 IU of D3 a day, median 5.3 years, no significant effect on total, nonvertebral or hip fractures [7]. A 2026 BMJ review of 69 trials found vitamin D alone had no effect on any fracture (36 trials, risk ratio 1.00, high certainty) [8] | No good evidence of benefit in adequately nourished people |
| Cancer and heart disease | VITAL: no lower risk of invasive cancer (hazard ratio 0.96) or major cardiovascular events (0.97) [9] | No good evidence of benefit |
| Respiratory infections | 2017 individual-data analysis: odds ratio 0.88, strongest with starting levels under 25 nmol/L [10]. 2025 update of 40 studies: odds ratio 0.94, not statistically significant [11] | Mixed |
| Supplementing without testing | Endocrine Society 2024 guideline suggests it for ages 1 to 18, adults over 75, pregnancy and high-risk prediabetes, and suggests against going above current intake references in healthy adults under 75 [12] | Guideline, not proof for everyone |
For the immune angle see Vitamin C, vitamin D and zinc.
Too much vitamin D
Toxicity almost always comes from supplements. [2] Too much can make the gut absorb too much calcium and raise blood calcium, causing confusion, nausea, vomiting, constipation, poor appetite, weakness, weight loss, kidney damage, kidney stones and calcium deposits in the heart and lungs. [2] The NHS says long-term excess can weaken bones and damage the kidneys and heart, and that you cannot overdose from sunlight. [1] VITAL, at 2,000 IU a day, found no excess hypercalcemia. [9] See Vitamin toxicity.Testing limits
Most tests measure 25-hydroxyvitamin D. [13] MedlinePlus pages give different ranges (levels below 30 to 50 nmol/L too low; 50 nmol/L or above enough for most people; elsewhere many experts recommend 75 to 200 nmol/L) and say ranges vary by lab. [2][3] The Endocrine Society found no trial evidence supporting routine testing in the general population and no clear target level for disease prevention. [12]Labels
Check mcg versus IU, the amount per serving and whether the form is D2 or D3. Combination products may add more. See Reading supplement labels and Quality testing and certifications.Frequently asked questions
How much vitamin D do I need?
It depends on country, age and health. The NHS (UK) lists 10 mcg (400 IU) for adults and children from 1; US reference intakes list 600 IU to age 70 and 800 IU after. Ask a clinician about your own situation. [1][2]
Is vitamin D3 better than D2?
This page does not rank them. MedlinePlus says they work similarly; see Vitamin D2 vs D3. [3]
Can I get enough from the sun?
In the UK, most people can from late March to September, but not October to early March; skin tone, clothing and sunscreen change this. [1]
Does vitamin D prevent colds?
Reviews disagree and the latest was not statistically significant. [10][11]
Can vitamin D be harmful?
Yes, in large amounts over time, mainly from supplements: it can raise blood calcium and harm the kidneys. [2][1]
More details: evidence, limits and cautions
The details behind this page: cautions, limits of the evidence and where sources disagree. Open any note to read it.
How to read the evidence labels
Labels used on this page: established nutritional role / deficiency treatment, evidence in adequately nourished people, mixed, no good evidence of benefit, insufficient evidence. A trial amount is a study amount, not advice. Proper evidence not found means we looked and found nothing usable.
Medicines, calcium and life-stage cautions
- Calcium: vitamin D increases calcium absorption, so ask a clinician before combining calcium supplements with vitamin D if you have a calcium-related condition. [2] See Calcium and Calcium plus vitamin D products.
- Medicines: MedlinePlus lists phenytoin, phenobarbital and rifampin as medicines that can lower vitamin D levels, and certain statins, steroids and weight-loss medicines as affecting levels. [3][13] Never stop a prescribed medicine on your own; see How interactions work.
- Pregnancy, babies, children: NHS pregnancy advice says not to take more than 100 mcg a day. [14] Babies and children have lower upper limits (table). Follow your midwife or pediatrician. See Children and teens.
- Kidney and liver disease: MedlinePlus says kidney and liver disease can affect the body's ability to turn vitamin D into a usable form; the NHS says some conditions mean you may not safely take as much, so follow your doctor. [13][1] See Vitamins and kidney or liver disease.
- Surgery and older adults: we found no vitamin D-specific surgery guidance in the sources read; see Vitamins before surgery and Vitamins for older adults.
References
- NHS (UK). Vitamins and minerals: Vitamin D. Page last reviewed 3 August 2020. Read 2026-10-22.
- MedlinePlus, U.S. National Library of Medicine. Vitamin D (encyclopedia article, reviewed 1/21/2025). Read 2026-10-22.
- MedlinePlus, U.S. National Library of Medicine. 25-hydroxy vitamin D test (encyclopedia article). Read 2026-10-22.
- NHS (UK). Rickets and osteomalacia. Read 2026-10-22.
- U.S. Food and Drug Administration. The Daily Value on the Nutrition and Supplement Facts Labels. Read 2026-10-22.
- European Food Safety Authority. Overview on Tolerable Upper Intake Levels as derived by the Scientific Committee on Food (SCF) and the EFSA NDA Panel. Version 11, August 2025 (Table 3, vitamins). Read 2026-10-22.
- LeBoff et al. 2022. Supplemental Vitamin D and Incident Fractures in Midlife and Older Adults (VITAL). N Engl J Med. PMID 35939577. Read 2026-10-22.
- Massé et al. 2026. Calcium, vitamin D, or combined supplementation to prevent fractures and falls: systematic review and meta-analysis. BMJ. PMID 42161415. Read 2026-10-22.
- Manson et al. 2019. Vitamin D Supplements and Prevention of Cancer and Cardiovascular Disease (VITAL). N Engl J Med. PMID 30415629. Read 2026-10-22.
- Martineau et al. 2017. Vitamin D supplementation to prevent acute respiratory tract infections: individual participant data meta-analysis. BMJ. PMID 28202713. Read 2026-10-22.
- Jolliffe et al. 2025. Vitamin D supplementation to prevent acute respiratory infections: systematic review and meta-analysis of stratified aggregate data. Lancet Diabetes Endocrinol. PMID 39993397. Read 2026-10-22.
- Demay et al. 2024. Vitamin D for the Prevention of Disease: An Endocrine Society Clinical Practice Guideline. J Clin Endocrinol Metab. PMID 38828931. Read 2026-10-22.
- MedlinePlus, U.S. National Library of Medicine. Vitamin D Test (medical test page). Read 2026-10-22.
- NHS (UK). Pregnancy vitamins and supplements. Read 2026-10-22.