Vitamin D

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By Nikola · Precision Nutrition L1 · Updated 5 November 2026

Vitamin D is a fat-soluble vitamin that helps your body absorb calcium and phosphorus and keeps bones, teeth and muscles working normally; your skin makes it in sunlight, and a few foods, above all oily fish, supply the rest. EFSA sets an adequate intake of 15 µg (600 IU) a day for adults, including pregnant and breastfeeding women, and in 2023 confirmed the adult upper limit of 100 µg (4,000 IU) a day. The 15 µg figure assumes that your skin makes little vitamin D; when your skin makes it, you need less from food. In autumn and winter, sunlight is weaker, which is why health services such as the NHS advise a daily supplement in those months.

What vitamin D does

There are two forms. Vitamin D3 (cholecalciferol) forms in the skin when UVB light converts a cholesterol-like compound, and it is also the form in fish and eggs. Vitamin D2 (ergocalciferol) comes from mushrooms and some supplements. Neither form is active as it is: the liver turns it into 25-hydroxyvitamin D, or 25(OH)D, the form a blood test measures, and the kidneys turn that into the active hormone calcitriol. Vitamin D helps the gut absorb calcium, keeps bones mineralised, and plays a part in muscle and nerve function, the immune system and inflammation (NIH ODS).

The EU allows these health claims for foods that are at least a source of vitamin D (Regulation (EU) 432/2012):

• “Vitamin D contributes to normal absorption/utilisation of calcium and phosphorus”
• “Vitamin D contributes to normal blood calcium levels”
• “Vitamin D contributes to the maintenance of normal bones”
• “Vitamin D contributes to the maintenance of normal muscle function”
• “Vitamin D contributes to the maintenance of normal teeth”
• “Vitamin D contributes to the normal function of the immune system”
• “Vitamin D has a role in the process of cell division”

How much you need a day

Group	EFSA adequate intake (AI), µg/day	EFSA upper limit, µg/day	For reference: NIH RDA, µg/day
Men and women	15 (600 IU)	100 (4,000 IU)	15 (19-70 years), 20 (over 70)
Pregnancy	15	100	15
Breastfeeding	15	100	15
Children 1-17 years	15	50 (1-10 years), 100 (11-17 years)	–
Infants 7-11 months	10	–	–

Sources: EFSA 2016 (adequate intake), EFSA 2023 (upper limit), NIH ODS. 1 µg of vitamin D equals 40 IU. EFSA based its intake on reaching a blood 25(OH)D level of 50 nmol/L, under conditions of minimal sun exposure. With regular skin synthesis, EFSA says the dietary need is lower and may even be zero. The 2023 upper limit rests on raised calcium in the urine seen at 250 µg a day in trials, divided by an uncertainty factor.

Best food sources

Food	Vitamin D, 100 g	Portion	Vitamin D per portion
Cod liver oil	250 µg (10,000 IU)	1 tsp, 4.5 g	11.3 µg
Atlantic mackerel, raw	16.1 µg (643 IU)	85 g	13.7 µg
Atlantic salmon, farmed, raw	11.0 µg (441 IU)	85 g	9.4 µg
Sardines, canned in oil, drained	4.8 µg (193 IU)	1 tin, 92 g	4.4 µg
Atlantic herring, raw	4.2 µg (167 IU)	85 g	3.6 µg
Egg, whole	2.0 µg (82 IU)	1 large, 50 g	1.0 µg
Beef liver, raw	1.2 µg (49 IU)	113 g	1.4 µg
Light tuna, canned in water	1.2 µg (47 IU)	85 g	1.0 µg
White mushrooms, raw	0.2 µg (7 IU), as D2	1 cup slices, 70 g	0.1 µg

Source: USDA FoodData Central, SR Legacy, checked 5 November 2026: cod liver oil FDC 173577, mackerel FDC 175119, salmon FDC 175167, sardines FDC 175139, herring FDC 175116, egg FDC 171287, beef liver FDC 169451, light tuna FDC 173709, white mushrooms FDC 169251. Portions are USDA household measures; values per portion are calculated and rounded.

Very few foods carry much vitamin D, so oily fish matter. One portion of mackerel comes close to the full 15 µg, and salmon covers more than half. Sardines, eggs and canned tuna add smaller amounts. Ordinary mushrooms have very little, but mushrooms exposed to UV light under controlled conditions have more vitamin D2 (NIH ODS). Cod liver oil is rich in vitamin D, but the same teaspoon also gives 1,350 µg RAE of vitamin A, almost half the adult upper limit for vitamin A. For a weekly habit: baked salmon with root vegetables or a Mediterranean mackerel stew.

Deficiency: signs and who is at risk

Long-term deficiency causes rickets in children, where bones fail to mineralise and become soft and deformed, and osteomalacia in adults, with weak bones; early bone pain and muscle weakness can be subtle. NIH describes blood 25(OH)D below 30 nmol/L as deficient, 30-50 nmol/L as generally inadequate, and 50 nmol/L or more as generally adequate.

How much your skin makes depends on season, time of day, cloud and shade, skin pigment and sunscreen. Full cloud cover cuts UV energy by about half, and UVB does not pass through window glass (NIH ODS). People most likely to run low:

• Breastfed babies, because breast milk alone usually does not cover their needs.
• Older adults, whose skin makes vitamin D less efficiently and who spend more time indoors.
• People who get little sun: housebound people, people who cover most of their skin outdoors and people in some occupations.
• People with darker skin, as melanin reduces vitamin D production.
• People with fat malabsorption, such as Crohn’s disease, coeliac disease or cystic fibrosis, and people after gastric bypass.
• People with obesity (BMI 30 or more), who tend to have lower blood levels.

Supplements: when they make sense

• Autumn and winter. The NHS says that in the UK people make enough vitamin D from sunlight from about late March or early April to the end of September, and advises everyone to consider 10 µg a day in autumn and winter. People at high risk should take it all year.
• Babies. The NHS advises a daily supplement of 8.5-10 µg for breastfed babies; in the US, the American Academy of Pediatrics recommends 400 IU (10 µg).
• D3 or D2. Both raise blood 25(OH)D. At ordinary doses they appear equivalent; at high doses D2 is less potent (NIH ODS).
• Testing. If you are in a risk group, ask your doctor about a 25(OH)D blood test before taking high doses.
• What it does not do. NIH concludes that studies to date do not support a role for vitamin D, with or without calcium, in lowering cancer risk.

Food and sunlight come first, and the upper limit of 100 µg a day counts everything together: supplements, fortified foods and fish.

Who should be careful

• Too much from supplements. Large doses over a long time can push blood calcium too high (hypercalcaemia). Early signs are vague: loss of appetite, weight loss, passing a lot of urine and heart rhythm problems; over time calcium can deposit in blood vessels and tissues. You cannot overdose on vitamin D from sunlight (NHS).
• Children. The upper limit for children aged 1-10 is 50 µg (2,000 IU) a day, half the adult value.
• Medicines. Orlistat and the cholesterol drug cholestyramine reduce vitamin D absorption. The epilepsy drugs phenobarbital and phenytoin speed up its breakdown, and corticosteroids such as prednisone can impair vitamin D metabolism and calcium absorption (NIH ODS).
• Cod liver oil. Because it is also rich in preformed vitamin A, it is not a good way to take large amounts of vitamin D, especially in pregnancy.

FAQ

How much vitamin D should I take a day?

EFSA’s adequate intake for adults is 15 µg (600 IU) a day from all sources, and the upper limit is 100 µg (4,000 IU). In autumn and winter, when the skin makes little, the NHS advises 10 µg a day as a supplement. Higher doses are a decision for your doctor, ideally after a blood test.

Is vitamin D3 better than D2?

Both forms raise blood levels of vitamin D. According to NIH, they appear equivalent at nutritional doses, while at high doses D2 is less potent.

Can you get enough vitamin D from the sun in winter?

It depends on where you live. The NHS says that in the UK people do not make enough vitamin D from sunlight between October and early March. Weak winter sun, clothing and time indoors all reduce skin production, so food and, if needed, a supplement have to fill the gap.

Related entries and articles

• Mackerel, salmon and sardines
• Eggs, mushrooms and canned tuna
• Vitamin A and vitamin K – the other fat-soluble vitamins
• Fish oil and omega-3 fatty acids
• How much vitamin D do you need?
• Baked salmon with root vegetables
• Mediterranean mackerel stew with tomatoes and olives

Sources

1. USDA FoodData Central, SR Legacy: Fish oil, cod liver (FDC 173577). fdc.nal.usda.gov
2. USDA FoodData Central, SR Legacy: Fish, mackerel, Atlantic, raw (FDC 175119); Fish, salmon, Atlantic, farmed, raw (FDC 175167); Fish, herring, Atlantic, raw (FDC 175116). fdc.nal.usda.gov
3. USDA FoodData Central, SR Legacy: Fish, sardine, Atlantic, canned in oil, drained solids with bone (FDC 175139); Fish, tuna, light, canned in water, drained solids (FDC 173709). fdc.nal.usda.gov
4. USDA FoodData Central, SR Legacy: Egg, whole, raw, fresh (FDC 171287); Beef, variety meats and by-products, liver, raw (FDC 169451); Mushrooms, white, raw (FDC 169251). fdc.nal.usda.gov
5. NIH Office of Dietary Supplements: Vitamin D, Fact Sheet for Health Professionals. ods.od.nih.gov
6. EFSA NDA Panel (2016). Dietary reference values for vitamin D. EFSA Journal, 4547. efsa.europa.eu
7. EFSA NDA Panel (2023). Scientific opinion on the tolerable upper intake level for vitamin D. EFSA Journal 21(8), doi 10.2903/j.efsa.2023.8145. doaj.org
8. EFSA: Overview on Tolerable Upper Intake Levels, version 11 (August 2025). efsa.europa.eu
9. Commission Regulation (EU) No 432/2012 – permitted health claims. eur-lex.europa.eu
10. NHS: Vitamin D. nhs.uk

This page is for information only and is not medical or dietary advice.