Is Vitamin D and D3 the Same? D2 vs D3, Explained

Two jars sit next to each other on the shelf. One says "Vitamin D 10 µg". The other says "Vitamin D3 4000 IU". They look like different products, and the question that follows is reasonable: are you comparing the same nutrient, or two different ones?

So: is vitamin D and D3 the same? Yes and no, in a way that matters when you are choosing between two jars. Here is what each word on that label is doing.

TL;DR

• D3 is a subset of vitamin D, not a different vitamin. Vitamin D is the umbrella term; D2 and D3 are the two members of the family.
• D3 is what your skin produces. UVB light converts 7-dehydrocholesterol in the skin into cholecalciferol — D3. D2 comes from fungi and UV-treated yeast.
• They are not equally effective at the same dose. In the Surrey D2–D3 trial, 15 µg a day for 12 weeks raised serum 25(OH)D by 74–75% as D3 and 33–34% as D2^[1].
• Micrograms and IU are the same number in different clothes. 10 µg = 400 IU. 25 µg = 1000 IU. 100 µg = 4000 IU.
• The NHS figure is 10 µg a day for adults and children over one, with a supplement advised through autumn and winter and all year for some groups^[2]. Most UK supplements, including our own vitamin D3 and K2 gummies, are labelled in IU rather than µg — the conversion is below.
• Vegan does not mean D2. D3 from lichen is vegan; D2 from yeast is vegan; the source, not the letter, decides.

Is vitamin D and D3 the same? What each name covers

Vitamin D is not one molecule. It is a small family of fat-soluble compounds that the body converts through the same two-step route, and two of them turn up in food and supplements: ergocalciferol, labelled D2, and cholecalciferol, labelled D3.

Both follow the identical path once swallowed. The liver converts either form into 25-hydroxyvitamin D — written 25(OH)D, and the thing a blood test measures. The kidney then converts that into 1,25-dihydroxyvitamin D, the active hormone the body uses. Nothing about that machinery is specific to D2 or D3; the difference shows up in how much 25(OH)D each form produces and how long it stays there.

So when a product says "vitamin D" and nothing else, it has told you the family and withheld the surname. Under the GB food information rules the declared nutrient name is simply "vitamin D", with no requirement to say which form supplies it^[8], which is why the ingredients line — cholecalciferol or ergocalciferol — is the part worth reading.

D2 and D3: where each one comes from

Do they work the same? The UK trial that measured it

This argument ran in the literature for years without resolution, largely because the older comparisons used enormous single doses that told you little about a daily supplement. In 2017 a team at the University of Surrey ran the comparison properly.

The D2–D3 Study was a randomised, double-blind, placebo-controlled food-fortification trial. It enrolled 335 healthy South Asian and white European women aged 20–64 and ran through a British winter.

Each participant took a daily placebo, or 15 µg of D2 or D3 delivered in either juice or a biscuit, for 12 weeks. Serum 25(OH)D was measured by liquid chromatography–tandem mass spectrometry at baseline, week six and week twelve^[1].

The placebo arm shows what a British winter does on its own. Everything else shows the gap between the two forms.

Two things are worth pulling out of that. First, the placebo group did not merely fail to improve — their vitamin D status fell by a quarter across the winter, which is the ordinary British seasonal pattern and the reason the supplement advice exists at all. Second, the delivery vehicle made almost no difference. Juice and biscuit landed within a percentage point of each other in both arms. The form of the vitamin was the variable that mattered.

A 2012 meta-analysis of the earlier randomised comparisons had already pointed the same way, concluding that D3 was the more effective of the two at raising 25(OH)D^[3]. The Surrey trial confirmed it at a dose an ordinary person might actually take.

Micrograms, IU and the number that confuses everyone

Half the difficulty in comparing two vitamin D products is that they rarely use the same unit. Micrograms (µg) are the legal unit on a GB nutrition label; international units (IU) are the convention in research papers and in a lot of imported packaging. IU is an older measure of biological activity rather than mass, which is why a US-facing pack tends to shout "5000 IU" where a British one states a quiet "125 µg" for the identical amount — and why a shelf of jars can look wildly inconsistent when it is not.

The conversion is fixed: 1 µg = 40 IU.

A jar advertising "4000 IU" is therefore sitting exactly at the NHS ceiling of 100 µg, not somewhere far above it — a useful thing to know before a big number frightens you off, and equally before you take two of them.

How much vitamin D the UK actually advises

The Scientific Advisory Committee on Nutrition set the current UK position in its 2016 report^[4], and the NHS states it plainly: children from the age of one and adults need 10 µg of vitamin D a day^[2].

Between roughly October and early March, UK sunlight is too weak at this latitude for the skin to make meaningful amounts, so the advice is that everyone — including people who are pregnant or breastfeeding — should consider a daily 10 µg supplement through autumn and winter^[2][5].

Some groups are advised to take it all year: people who are not often outdoors, people living in a care home, people who usually wear clothing that covers most of their skin, and people with dark skin — for example an African, African-Caribbean or South Asian background — because more melanin means less vitamin D synthesised from the same amount of light^[2].

The ceiling matters too. The NHS advises adults and children aged 11–17 not to take more than 100 µg (4000 IU) a day, with lower limits of 50 µg for children aged 1–10 and 25 µg for infants under one. Taking too much over a long period causes calcium to build up in the blood^[2], which is why "more is better" is the wrong instinct with this particular vitamin.

If you want the fuller picture of what low status looks like and who is most affected, our guide to vitamin D deficiency in the UK covers the symptoms and the testing question, and NICE sets out how clinicians here approach it^[7].

Is vegan vitamin D always D2?

It used to be, and it is not any more. The traditional commercial source of D3 is lanolin — the grease from sheep's wool — which makes it unsuitable for a vegan diet, and for years D2 from UV-treated yeast was the only vegan option. That is where the "D2 is the vegan one" shorthand comes from.

D3 can now be extracted from lichen, a symbiotic organism of fungus and alga, giving a cholecalciferol that is vegan by source. A vegan supplement can therefore be D2 or D3, and the trial evidence above is the reason a plant-source D3 is generally the more useful of the two.

That is the choice behind our own formulation. Vitgem's vitamin D3 and K2 gummies are built on lichen-derived cholecalciferol rather than lanolin D3, so the same form the skin makes is available to a vegan diet without dropping to D2 and its weaker measured effect. The D3 sits alongside vitamin K2 as MK-7, and the reasoning behind pairing the two — vitamin D contributes to normal absorption and utilisation of calcium, vitamin K contributes to the maintenance of normal bones — is set out in our piece on how vitamin K2 and vitamin D3 work together.

What a UK label is allowed to claim

Vitamin D is one of the better-served nutrients in the GB register of authorised health claims^[6], which means a supplement carrying enough of it may legally state that it:

• contributes to normal absorption and utilisation of calcium and phosphorus;
• contributes to normal blood calcium concentrations;
• contributes to the maintenance of normal bones, teeth and muscle function;
• contributes to the normal function of the immune system;
• has a role in the process of cell division.

Those wordings apply to vitamin D as a nutrient. There is no separate register entry for "D3" that permits a stronger sentence, so a jar of D3 and a jar of D2 that both hit the required amount may say exactly the same things. The difference between them is in the blood test, not on the front of the pack — and no food supplement of either form may be presented as preventing, treating or curing any disease. The same rule governs every other nutrient in our range of gummy vitamins, whichever letter is on the jar.

Frequently asked questions

Is vitamin D and vitamin D3 the same thing?

Not quite. Vitamin D3 is one of the two forms of vitamin D, the other being D2. A label that says only "vitamin D" may legally contain either, so the ingredients list — cholecalciferol for D3, ergocalciferol for D2 — is where the answer is.

Which is better, vitamin D or D3?

The comparison that makes sense is D3 against D2. In a 12-week randomised UK trial at 15 µg a day, D3 raised blood 25(OH)D by roughly twice as much as D2 at the same dose.

Can I take vitamin D3 if I am vegan?

Yes, if it is lichen-derived. D3 from lanolin is a sheep's-wool product and is not vegan; lichen D3 is chemically the same cholecalciferol from a plant-kingdom source.

How many micrograms is 4000 IU of vitamin D3?

100 micrograms. The conversion is 1 µg = 40 IU, and 100 µg a day is the upper limit the NHS gives for adults.

Do I need vitamin D in summer?

Most people in the UK can make enough from sunlight between late March and September, which is why the NHS advice focuses on autumn and winter. People who are rarely outdoors, who cover their skin, or who have dark skin are advised to take a supplement all year.

Is D3 better absorbed than D2?

The measured difference is in the resulting blood level rather than absorption alone. D3 appears to raise and maintain serum 25(OH)D more effectively, which is what both the Surrey trial and the earlier meta-analysis found.

This article is general information about nutrition and food supplements, not medical advice. If you are taking prescribed medication, are pregnant or breastfeeding, or have a medical condition, speak to your GP or pharmacist before starting a supplement.