Vitamin D2 vs Vitamin D3: What's the Difference?

Vitamin D has one of those labels that looks simple until you compare two bottles. One says D2. Another says D3. Then you find people online saying D3 is better, while another product proudly uses D2. It is easy to turn a small difference in chemistry into a much bigger argument than the evidence supports.

The useful version is simpler. D2 and D3 are both genuine forms of vitamin D. They follow much of the same pathway in the body, but they are not identical, and the difference can matter when researchers measure how much total 25-hydroxyvitamin D, or 25(OH)D, rises in the blood.

What do D2 and D3 actually mean?

Vitamin D2 is called ergocalciferol. Vitamin D3 is called cholecalciferol. After absorption, both forms can be converted into vitamin D metabolites in the body, and blood 25(OH)D is commonly used as the main marker of vitamin D status.[1][2]

The names therefore describe the form of vitamin D, not a separate vitamin with a completely different job. If a label says 'vitamin D', the ingredient panel or specification may tell you whether that vitamin D is D2 or D3.

Where does vitamin D2 come from?

Vitamin D2 is associated mainly with fungi and yeast. UK scientific guidance notes that D2 used in supplements or fortified foods can be produced from fungi and UVB-irradiated yeast. Mushrooms can also contain vitamin D2, especially after exposure to ultraviolet light.[3][4]

That makes D2 a naturally useful option for products intended to avoid animal-derived vitamin D sources.

Where does vitamin D3 come from?

Vitamin D3 is the form produced in human skin after suitable UVB exposure. In supplements, D3 is most commonly derived from lanolin extracted from sheep's wool. There is also a vegan source of D3 obtained from lichen, so seeing 'D3' on a label does not automatically tell you whether the finished product is vegan.[3]

Which one raises vitamin D status more effectively?

This is the part that has been studied most directly. A 2021 systematic review and meta-analysis included 24 comparative studies and found that vitamin D3 was more effective than D2 at increasing total 25(OH)D overall.[1]

A newer systematic review and meta-analysis published in Advances in Nutrition reached the same broad conclusion. Across 20 comparative studies, D3 produced a greater rise in total 25(OH)D than D2 overall. Baseline vitamin D status and body mass index were also important response modifiers in the daily-dose comparisons.[2]

That is a much more useful conclusion than saying 'D2 does not work'. D2 still raises vitamin D metabolites. The evidence simply suggests that, dose for dose, D3 tends to be more effective at raising total 25(OH)D.

Does D3 being more effective mean everyone needs D3?

Not necessarily. A supplement still has to fit the person taking it. Dietary preferences, the dose, how often it is taken, other sources of vitamin D and professional advice can all matter. The research comparing D2 with D3 is about average changes in vitamin D status across study groups, not a promise about exactly how one person will respond.

Does the form change the IU-to-microgram conversion?

No. This is a separate issue from D2 versus D3. For vitamin D, 1 microgram equals 40 IU. That conversion applies whether the label is describing vitamin D2 or vitamin D3.[5]

So 25 micrograms of D2 is 1,000 IU, and 25 micrograms of D3 is also 1,000 IU. The form may influence the biological response, but it does not change the unit conversion.

How should you compare two vitamin D supplements?

1. Put both products into the same unit. If one uses IU and the other uses micrograms, convert them before comparing.
2. Check whether the ingredient is D2 or D3.
3. If vegan suitability matters, check the actual source of D3 rather than assuming all D3 is animal-derived.
4. Compare the recommended daily serving, not just the amount printed most prominently on the front.
5. Treat the form as one piece of the label, alongside dose, directions, warnings and your total vitamin D intake.