How much vitamin D should you take a day?

The EU labelling reference value is 5 micrograms (200 IU), which is a low figure: common presentations range from 1000 to 4000 IU because they are designed to correct low intakes. The dose that suits you depends on your blood levels, which is why this is a supplement worth adjusting with a blood test rather than guessing.

How many IU are in a microgram?

1 microgram is 40 IU, so 1000 IU is 25 micrograms and 4000 IU is 100. It is the conversion you need to compare two tubs, because labels mix both units and the reference value percentage is calculated on micrograms.

Is vitamin D3 or D2 better?

D3 (cholecalciferol) is more effective at maintaining blood levels than D2 (ergocalciferol). D3 usually comes from lanolin, although there are vegan versions from lichen. For the same price, D3.

Can you take too much vitamin D?

Yes. It is fat-soluble, builds up in the body and at sustained high doses can raise blood calcium. It is not a risk at normal supplement doses, but it is a reason not to stack several tubs containing it or take megadoses on your own.

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Vitamin D · Moderate evidence

What vitamin D is for and how much to take

The short answer. Vitamin D is not exactly a vitamin: the skin makes it in sunlight, which is why it is the most common deficiency in people who spend the day indoors or live far from the equator. EU regulation recognises its role in bones, muscles and the immune system. As a supplement it has a clear case (low intake or little sun exposure) and a common trap: the units, which some labels give in micrograms and others in IU.

There are studies in favour, but few, with small samples or measuring markers instead of outcomes. No figure on this page is attributed to a specific product: the effect belongs to the ingredient and every number carries its source next to it.

01 What it does and how much

Each row is a measured effect, with the figure the study gives and the source number. Where the evidence gives no figure, the column says so instead of making up a percentage.

Effects of vitamin D with their source
Effect	How much	Detail
EU daily reference value	5 micrograms (200 IU)	It is the labelling NRV, and it is low compared with the doses used to correct a deficiency. That is why many tubs declare percentages in the hundreds. [1]
Functions authorised in the EU	bones, muscle and immunity	It contributes to the maintenance of normal bones and teeth, normal muscle and immune system function and normal calcium absorption. [2]
Unit conversion	1 microgram = 40 IU	It is the conversion to keep at hand: 1000 IU is 25 micrograms. Without it you cannot compare two tubs. [1]
Without a deficiency	no effect on performance	The same rule as all micronutrients. The difference is that here deficiency is far more common than it seems. [3]

02 How to take it

Dose. Whatever your blood test calls for. Common presentations range from 1000 to 4000 IU.
When. With a meal containing fat: it is fat-soluble and absorbed worse without fat.
How long before you notice it. Weeks or months to raise blood levels.

Details that change the result

It is fat-soluble and builds up: here more is not better, and sustained high doses without medical supervision are not harmless.
D3 (cholecalciferol) maintains levels better than D2. There is vegan D3 from lichen for those who need it.
Skin synthesis depends on latitude, season, time of day and sunscreen. In winter, in the north, there is practically none.
It is measured in blood (25-OH vitamin D). It is one of the few things on this site with an objective, cheap answer.

03 When it makes sense and when it does not

Worth it if

Months with barely any sun exposure: indoor work, long winters, little time outdoors.
Very dark skin at high latitudes, where skin synthesis is lower.
Deficiency confirmed in a blood test or medical advice.

Not worth it if

At high doses indefinitely and without monitoring: it builds up.
Expecting an effect on performance if your levels are already normal.
Stacking several tubs (multivitamin, calcium with D, omega 3 with D) without adding up the total.

04 Sources

Every figure above comes from here. They are position stands from scientific societies, meta-analyses and peer-reviewed reviews: if a claim cannot hang from one of these lines, it is not on the page. References are cited in their original form.

Reglamento (UE) 1169/2011, Anexo XIII: valores de referencia de nutrientes. Vitamina D, 5 microgramos. https://eur-lex.europa.eu/legal-content/ES/TXT/?uri=CELEX%3A32011R1169
Reglamento (UE) 432/2012: declaraciones autorizadas. La vitamina D contribuye al mantenimiento de huesos y dientes normales, al funcionamiento normal de los musculos y del sistema inmunitario y a la absorcion y utilizacion normales del calcio. https://eur-lex.europa.eu/legal-content/ES/TXT/?uri=CELEX%3A32012R0432
Kerksick CM et al. ISSN exercise & sports nutrition review update. J Int Soc Sports Nutr. 2018;15:38. Los micronutrientes mejoran el rendimiento solo cuando corrigen un deficit. doi:10.1186/s12970-018-0242-y

This is not medical advice. It is what some studies say about an ingredient, not a protocol for you. With an illness, medication or pregnancy involved, the decision belongs to a healthcare professional who knows you.

Questions about vitamin D

Answered with the data on this page

How much vitamin D should you take a day?: The EU labelling reference value is 5 micrograms (200 IU), which is a low figure: common presentations range from 1000 to 4000 IU because they are designed to correct low intakes. The dose that suits you depends on your blood levels, which is why this is a supplement worth adjusting with a blood test rather than guessing.
How many IU are in a microgram?: 1 microgram is 40 IU, so 1000 IU is 25 micrograms and 4000 IU is 100. It is the conversion you need to compare two tubs, because labels mix both units and the reference value percentage is calculated on micrograms.
Is vitamin D3 or D2 better?: D3 (cholecalciferol) is more effective at maintaining blood levels than D2 (ergocalciferol). D3 usually comes from lanolin, although there are vegan versions from lichen. For the same price, D3.
Can you take too much vitamin D?: Yes. It is fat-soluble, builds up in the body and at sustained high doses can raise blood calcium. It is not a risk at normal supplement doses, but it is a reason not to stack several tubs containing it or take megadoses on your own.

And now, which to buy

Prices, kept apart from the evidence

This page explains what vitamin D does and deliberately names no brand. The comparison is the other half: 137 products from 12 stores from €0.022 per capsule, sorted by price and by how verifiable their certification is.

See the vitamin d comparison

Other guides

What each supplement does, with its sources