Vitamins
Vitamin D
Vitamin D is a fat-soluble vitamin. The term mainly covers vitamins D₂ and D₃; your body can produce D₃ in the skin through exposure to UVB radiation.
Vitamin D is an umbrella term for a group of related compounds rather than a single substance. Its main nutritional forms are vitamin D₂ (ergocalciferol) and vitamin D₃ (cholecalciferol, also spelt colecalciferol). Both forms occur in foods and supplements, and vitamin D can also be added to fortified foods. A distinctive feature is that your body can produce vitamin D₃ in the skin through exposure to UVB radiation. Chemically, these forms belong to the secosteroid family. Vitamin D is a micronutrient, not a food in itself. The name alone does not identify the biological source of vitamin D added to a product.
Vitamin D: from food and from your skin
Vitamin D is a fat-soluble vitamin. The name covers several related compounds; its main nutritional forms are vitamin D₂ (ergocalciferol) and vitamin D₃ (cholecalciferol). Both occur in foods and preparations and can be added to fortified foods. A distinctive feature is that your skin can produce vitamin D₃ through exposure to UVB radiation.
What vitamin D does in your body
Vitamin D contributes to normal calcium and phosphorus absorption and utilisation, and to normal blood calcium levels. It supports the maintenance of normal bones and teeth, normal muscle and immune function, and has a role in cell division. These functions are authorised health claims under Regulation (EU) No 432/2012 for foods meeting at least the conditions for being a source of vitamin D. Supporting normal body function is not the same as gaining extra benefits from more vitamin D: additional supplements do not automatically help when vitamin D status is already adequate.
Before vitamin D exerts its hormonal effects, it is converted first in the liver to 25-hydroxyvitamin D, then primarily in the kidneys to its active form, calcitriol. Fat in a meal enhances intestinal absorption, although some vitamin D is absorbed without dietary fat. A particularly high-fat meal is not necessary.
How much vitamin D do you need?
With sufficient vitamin D production in the skin, the intake needed may be lower. Skin production varies with factors including season, time of day, skin pigmentation and age. Sunlight through window glass does not enable this production. Because UV exposure also increases skin-cancer risk, there is no universally safe and sufficient duration of sun exposure.
Blood results need interpretation
The main indicator of vitamin D status is serum 25-hydroxyvitamin D, or 25(OH)D. It reflects both skin production and intake. A universally optimal blood concentration for overall health has not been clearly established. Evidence is also insufficient to determine the balance of benefits and harms of routine testing in adults without symptoms. Testing may be appropriate for a specific medical concern; the result needs clinical interpretation.
Seek medical advice before supplementing if you have kidney disease, a history of kidney stones, sarcoidosis or hyperparathyroidism, or take medicines such as thiazide diuretics or digoxin. Count vitamin D from different preparations together. Check the dose per drop, and never take a prescribed weekly or monthly dose daily by mistake.
How nutrition works
Bone health
Muscle function
Dental health
Vitamin D contributes to the maintenance of normal teeth. [1]
Immune system
Cell division
Glycaemic control
Calcium and phosphorus metabolism
Cardiovascular health
In adults aged 50–74 years, vitamin D supplements have not been shown to reduce cardiovascular events. [5]
Statements & evidence
Vitamin D contributes to normal absorption/utilisation of calcium and phosphorus [1]
This authorised claim may only be used for foods that qualify as at least a source of vitamin D under EU rules. It does not mean that additional supplements improve absorption beyond normal function.
Vitamin D contributes to normal blood calcium levels [1]
The claim is authorised for foods that qualify as at least a source of vitamin D. It is not a claim that abnormal blood calcium can be corrected by self-administering vitamin D supplements.
Vitamin D is fat-soluble. Its two main forms in foods and supplements are vitamin D₂ (ergocalciferol) and vitamin D₃ (cholecalciferol). [7]
Both forms can contribute to vitamin D intake. D₂ and D₃ describe different chemical forms, rather than separate vitamins with entirely different roles.
Your skin can produce vitamin D₃ through exposure to UVB radiation; sunlight through window glass does not enable this production. [7]
Production varies with factors including season, time of day, skin pigmentation and age. UV exposure also increases skin-cancer risk, so this fact does not establish a universally safe or sufficient duration of sun exposure.
Vitamin D is converted first in the liver to 25-hydroxyvitamin D, then primarily in the kidneys to its active form, calcitriol. [7]
Vitamin D from food, supplements or skin synthesis undergoes these conversion steps before exerting its hormonal effects.
Fat in a meal enhances vitamin D absorption, although some vitamin D is also absorbed without dietary fat. [7]
Fat supports intestinal absorption of this fat-soluble vitamin. This does not mean that a particularly high-fat meal is necessary.
Serum 25-hydroxyvitamin D, or 25(OH)D, is the principal indicator used to assess vitamin D status. [7]
The measurement reflects both skin synthesis and intake. It requires clinical interpretation and does not, by itself, justify routine testing.
Assuming minimal skin synthesis, EFSA sets an adequate vitamin D intake of 15 µg daily from one year of age, including pregnancy and lactation, and 10 µg daily for infants aged 7–11 months. [8]
These values concern intake from foods and, where used, supplements. They are reference values, not universal supplement doses. With sufficient skin synthesis, the required dietary intake may be lower.
The EU adult nutrient reference value for vitamin D on food labels is 5 µg; this differs from EFSA's adequate-intake reference value. [9][8]
The labelling value is set in Annex XIII of Regulation (EU) No 1169/2011. Percentages on packaging refer to this value, not to EFSA's 15 µg adequate intake under conditions of minimal skin synthesis.
EFSA sets the tolerable upper intake level at 100 µg vitamin D equivalents daily for adults, including pregnancy and lactation, and adolescents aged 11–17 years. For children aged 1–10 years, it is 50 µg daily. [10]
These values from the 2023 assessment apply to long-term total intake from foods and supplements, not to skin synthesis. They are safety limits, not intake targets or recommended supplement doses.
A universally optimal vitamin D blood concentration for overall health has not been clearly established. [7]
Thresholds for adequate status and a proposed optimum are not the same thing. Differences between laboratory assays also affect interpretation of results.
Evidence is insufficient to determine the balance of benefits and harms of routine vitamin D screening in adults without symptoms. [7]
This uncertainty concerns routine testing without symptoms. It does not mean that testing is unnecessary when there is a specific medical concern or another clinical indication.
Safety information
Upper level · Adults
Upper intake level for adults
EFSA sets an upper intake level of 100 µg vitamin D equivalents daily for adults, including pregnancy and breastfeeding. For vitamin D₂ or D₃, this equals 4,000 IU. It covers habitual total intake from foods and supplements, not a recommended daily dose. Higher treatment doses require medical supervision. [10][7][12]
Upper level
Age-specific upper limits for children
EFSA's upper intake level is 50 µg vitamin D equivalents daily for children aged 1–10 years and 100 µg for those aged 11–17 years. For vitamin D₂ or D₃, these equal 2,000 and 4,000 IU respectively. These limits cover total intake and are not recommended supplement doses. [10][7]
Upper level
Lower upper limits for infants
EFSA's upper intake level is 25 µg vitamin D daily below 6 months and 35 µg from 6 to under 12 months. For vitamin D₂ or D₃, these equal 1,000 and 1,400 IU respectively. Intake from infant formula and supplements counts together; the upper limit is not a dosing recommendation. [11][7]
Caution
Calcidiol is not dose-equivalent to D₃
If your preparation contains calcidiol monohydrate, do not substitute it microgram-for-microgram for vitamin D₃. EFSA uses a factor of 2.5 to convert calcidiol monohydrate into vitamin D equivalents. Ask a healthcare professional to check any switch between preparations. [10]
Side effect
Excess intake can disrupt calcium balance
Too much vitamin D, usually from excessive supplement doses, can raise calcium in blood and urine. Severe toxicity can damage the kidneys and cause abnormal heart rhythms. If overdose is suspected, or you develop persistent vomiting, marked thirst, frequent urination or confusion, seek prompt medical assessment and stop supplementary vitamin D pending review. [10][7][12]
Side effect
Possible symptoms and preparation allergies
Stomach pain, nausea and headache are reported with colecalciferol preparations. Some formulations may be unsuitable if you have peanut or soya allergy; check the ingredients. Serious allergic reactions are rare: breathing difficulty or swelling of the mouth or throat requires emergency help. [13][14]
Caution · Adults
Higher doses are not automatically better
Some very high monthly or annual vitamin D doses increased falls or fractures in trials, particularly in older adults. A review of 3,200–4,000 IU daily also found more hypercalcaemia and signals for more falls and hospital admissions. These findings do not apply to every prescribed regimen; do not start high-dose regimens yourself. [10][15]
Caution
Seek advice with kidney disease or kidney stones
If you have kidney disease or a history of kidney stones, seek medical advice before supplementing vitamin D. The preparation, dose and monitoring depend on kidney function and calcium balance. Severe kidney disease does not rule out all medically supervised vitamin D treatment. Trials do not consistently show more kidney stones from vitamin D alone. [14][16]
Caution
Extra caution with sarcoidosis and calcium disorders
If you have sarcoidosis or hyperparathyroidism, do not supplement vitamin D without medical advice. Sarcoidosis can increase the formation of active vitamin D and raise calcium levels; blood and sometimes urine calcium monitoring may be needed. General upper intake limits do not guarantee individual safety in these conditions. [17][7]
Contraindication
Contraindications depend on the preparation
EMA information for the calcium/vitamin D₃ combination Calcichew-D₃ lists raised blood or urine calcium, kidney stones, hypervitaminosis D, severe renal impairment and hypersensitivity among its contraindications. This list concerns that specific combination, not automatically every vitamin D preparation. Check your product information with a healthcare professional. [17]
Interaction
Thiazide diuretics can increase calcium-related risk
Thiazide diuretics reduce urinary calcium excretion. Combined with vitamin D, they can raise blood calcium, particularly in older people or those with impaired kidney function or hyperparathyroidism. Ask your clinician to review the combination and whether calcium monitoring is needed; do not stop prescribed medicines yourself. [7]
Interaction
Calcium monitoring matters with digoxin
If you take digoxin or another cardiac glycoside, have vitamin D supplementation reviewed by your clinician, especially when combined with calcium. Raised calcium can increase cardiac-glycoside toxicity and the risk of abnormal heart rhythms. Calcium checks and sometimes ECG monitoring may be needed. [17]
Interaction
Some medicines reduce absorption or effect
Orlistat, cholestyramine and liquid-paraffin laxatives can reduce vitamin D absorption. Corticosteroids and some epilepsy medicines, such as phenytoin, carbamazepine, phenobarbital or primidone, can reduce its effects. Have your medicines reviewed rather than increasing the vitamin D dose yourself. [7][18]
Caution
Check the dose per drop for children
In infants and young children, dosing errors with concentrated vitamin D drops can cause severe poisoning and calcium deposits in the kidneys. Check the IU per drop, avoid duplicate products and do not replace a prescribed medicine with a supplement of a different concentration without professional advice. [19]
Caution
Treatment doses need a clear dosing plan
High-dose medical treatment needs a clear plan for dose, interval, duration and monitoring. Never take a weekly or monthly dose daily by mistake, or continue an initial loading dose indefinitely. Count vitamin D in multivitamins and calcium combination products as well. [12]
Frequently asked questions
What does my body need vitamin D for?
Vitamin D contributes to maintaining normal bones and teeth, and to normal muscle and immune function. It also supports normal calcium and phosphorus absorption and utilisation; extra supplements do not automatically provide further benefits when your vitamin D status is adequate.
How much vitamin D do I need each day?
Assuming minimal vitamin D production in the skin, EFSA sets an adequate intake of 15 µg daily for adults, including during pregnancy and breastfeeding. This is a reference value for total intake from foods and any supplements, not a universal supplement dose; sufficient skin production may reduce the intake needed.
Can I make vitamin D from sunlight through a window?
No, sunlight through window glass does not enable vitamin D production in your skin, because this requires UVB radiation. Production outdoors varies with season, time of day, skin pigmentation and age, so there is no universally safe and sufficient duration of sun exposure.
Should I have my vitamin D level tested?
Evidence is insufficient to determine the balance of benefits and harms of routine vitamin D testing in adults without symptoms. Testing may be appropriate for a specific medical concern; the main measurement is 25-hydroxyvitamin D, or 25(OH)D, and the result needs clinical interpretation.
Can I take too much vitamin D?
Yes, excessive supplement doses can raise calcium levels and, in severe toxicity, damage the kidneys. EFSA's adult upper limit is 100 µg vitamin D equivalents daily from foods and supplements combined; for D₂ or D₃, this equals 4,000 IU and is not a recommended daily dose. If you suspect an overdose, stop supplementary vitamin D and seek prompt medical assessment.
More entries
Folate
Folate is a water-soluble B vitamin. Its active forms take part in DNA synthesis and amino-acid metabolism.
Vitamin A
Vitamin A is an essential, fat-soluble vitamin. Your diet supplies it as preformed vitamin A or as precursors from plant foods.
Vitamin B12
Vitamin B12 is an essential, water-soluble vitamin. Your body needs it for normal nervous-system function, red blood cell formation and DNA synthesis.
Vitamin C
Vitamin C is an essential, water-soluble vitamin that you need to obtain through your diet. Its principal chemical form is L-ascorbic acid.
Vitamin K
Vitamin K is an essential, fat-soluble vitamin. Your body needs it to activate proteins involved in blood clotting and bone metabolism.
Vitamin B6
Vitamin B6 is a water-soluble vitamin. Its active forms support many metabolic processes, particularly amino-acid metabolism.
Sources
- 01European Commission · 2012Commission Regulation (EU) No 432/2012 establishing a list of permitted health claims made on foods, other than those referring to the reduction of disease risk and to children's development and healthOpen source
- 02EFSA Journal · 2016Dietary reference values for vitamin DDOI 10.2903/j.efsa.2016.4547
- 03The BMJ · 2026Calcium, vitamin D, or combined supplementation to prevent fractures and falls: systematic review and meta-analysisOpen source
- 042025Vitamin D supplementation to prevent acute respiratory infections: systematic review and meta-analysis of stratified aggregate dataPubMed 39993397Open source
- 05The Journal of Clinical Endocrinology & Metabolism · 2024A Systematic Review Supporting the Endocrine Society Clinical Practice Guidelines on Vitamin DOpen source
- 062023Vitamin D and Risk for Type 2 Diabetes in People With PrediabetesOpen source
- 07National Institutes of Health, Office of Dietary SupplementsVitamin D - Health Professional Fact SheetOpen source
- 08European Food Safety Authority · 2016Vitamin D: EFSA sets dietary reference valuesOpen source
- 09European Parliament and Council of the European Union · 2011Regulation (EU) No 1169/2011 on the provision of food information to consumersOpen source
- 10EFSA Journal · 2023Scientific opinion on the tolerable upper intake level for vitamin D, including the derivation of a conversion factor for calcidiol monohydrateDOI 10.2903/j.efsa.2023.8145
- 11EFSA Journal · 2018Update of the tolerable upper intake level for vitamin D for infantsDOI 10.2903/j.efsa.2018.5365
- 12NHS Specialist Pharmacy ServiceSafety considerations when using Vitamin DOpen source
- 13NHSSide effects of colecalciferolOpen source
- 14NHSWho can and cannot take colecalciferolOpen source
- 152023Long-term supplementation with 3200 to 4000 IU of vitamin D daily and adverse events: a systematic review and meta-analysis of randomized controlled trialsOpen source
- 16Hypercalcemia, hypercalciuria, and kidney stones in long-term studies of vitamin D supplementation: a systematic review and meta-analysisPubMed 27604776Open source
- 17European Medicines Agency · 2004Calcichew-D3 and associated names: Article 30 referral, Annexes I, II and IIIOpen source
- 18NHSTaking colecalciferol with other medicines and herbal supplementsOpen source
- 19Vigil’Anses · 2023Vigil’Anses No. 19 — June 2023: Vitamin DOpen source
- 202026Calcium, vitamin D, or combined supplementation to prevent fractures and falls: systematic review and meta-analysisOpen source
- 21European Commission · 2014Commission Regulation (EU) No 1228/2014 authorising and refusing to authorise certain health claims made on foods and referring to the reduction of disease riskOpen source
- 222024Effect of vitamin D supplementation on cardiovascular outcomes: an updated meta-analysis of RCTsOpen source
- 232023Efficacy of vitamin D3 supplementation on cancer mortality: Systematic review and individual patient data meta-analysis of randomised controlled trialsOpen source
- 242019Vitamin D and Calcium for the Prevention of Fracture: A Systematic Review and Meta-analysisPubMed 31860103Open source
- 25Scientific Advisory Committee on Nutrition · 2016Vitamin D and HealthOpen source
- 26Journal of Bone and Mineral Research · 2021Vitamin D and Muscle Health: A Systematic Review and Meta-analysis of Randomized Placebo-Controlled TrialsDOI 10.1002/jbmr.4412
- 272022Vitamin D supplementation for the prevention of total cancer incidence and mortality: An updated systematic review and meta-analysisOpen source