Two letters, one number's difference. On a UK supplement shelf, vitamin D appears as D2 or D3 — ergocalciferol or cholecalciferol — and the choice between them is one of the few label questions that actually matters once you've decided to take vitamin D at all.
Both are vitamin D. Both contribute to the same body of authorised health claims on the Great Britain Nutrition and Health Claims Register, including, notably, that vitamin D contributes to the maintenance of normal bones. They are not, however, interchangeable in every respect, and the differences are worth knowing before you compare two bottles.
This is not a piece about which is "better." It is about what each one is, where it comes from, and what the evidence says about how the body handles them.
Two molecules, one vitamin
Vitamin D3 — cholecalciferol — is the form your skin produces when UVB radiation reaches it. It is also the form in oily fish, egg yolks, liver, and the small handful of fortified foods that contribute meaningfully to UK intake. In supplements, D3 has historically been extracted from lanolin (sheep's wool), and more recently from lichen for vegetarian and vegan-suitable products.
Vitamin D2 — ergocalciferol — comes from a different starting point. UV light acting on ergosterol, a compound found in yeast and fungi, produces D2. In supplements, the source is usually UV-exposed yeast or mushrooms, which makes D2 a plant-based option by default.
Neither form is active when you swallow it. The liver converts each one into 25-hydroxyvitamin D — 25(OH)D, the marker your GP would measure in a blood test — and the kidney then converts that into the active hormone 1,25-dihydroxyvitamin D. The conversion machinery is the same regardless of which form started the journey.
What the research actually says
In 2012, Tripkovic and colleagues published a meta-analysis in the American Journal of Clinical Nutrition that pooled randomised trials comparing D2 and D3. The headline finding: D3 generally produced a greater rise in serum 25(OH)D than equivalent amounts of D2, though both forms raised circulating levels. Later reviews have largely echoed that pattern, while pointing out that the gap depends on amount, frequency, baseline status, and trial design.
UK clinical practice tracks the evidence. NHS treatment guidance uses cholecalciferol (D3) as standard, with ergocalciferol (D2) reserved for specific cases — for instance, where someone cannot take colecalciferol for cultural, dietary, or medical reasons.
None of this means D2 doesn't work. It is recognised, regulated, and prescribed where appropriate. It does mean the two forms shouldn't be treated as identical on a one-to-one basis, and that, in the UK at least, D3 is the more commonly used form for raising and maintaining 25(OH)D.
The same claims apply to both
This is the bit most readers don't realise: the authorised health claims on the Great Britain Nutrition and Health Claims Register apply to vitamin D as a nutrient. A supplement that meets the minimum threshold can carry them whether it contains D2, D3, or a combination.
- Vitamin D contributes to the normal function of the immune system.
- 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 normal absorption and utilisation of calcium and phosphorus.
- Vitamin D contributes to normal blood calcium levels.
- Vitamin D has a role in the process of cell division.
The wording is the wording. It cannot be paraphrased into something punchier and stay within the Register.
Source matters, separately from form
Form (D2 vs D3) is one question. Source is another, and the two get conflated.
Vitamin D3 from lanolin is animal-derived. It comes from sheep's wool, which makes it acceptable to most vegetarians but unsuitable for vegans. Vitamin D3 from lichen is plant-based and works for both groups. Vitamin D2 from yeast is plant-based as well. A label that says "vegetarian" tells you something; one that names the actual source (lichen, lanolin, yeast) tells you more.
If a product doesn't say where its D3 comes from, that absence is information too.
Reading two labels
If you're looking at two vitamin D supplements and trying to decide between them, the front of the bottle is the marketing. The back is the document. Four things to check, in roughly this order:
The form — D3 (cholecalciferol) or D2 (ergocalciferol). The source — lichen, lanolin, yeast. The amount per serving, in micrograms, with International Units alongside if shown (1 µg of vitamin D = 40 IU). And the rest of the ingredient list, which is where carriers, capsule materials, and any other additions live.
That's usually enough to tell you what's actually in front of you.
Vitamin D and the bones picture
One of the authorised claims is that vitamin D contributes to the maintenance of normal bones. A separate authorised claim — vitamin D contributes to the normal absorption and utilisation of calcium and phosphorus — describes part of the underlying mechanism.
That double claim is part of why vitamin D rarely appears alone on the bone-relevant nutrients list. Calcium contributes its own authorised bone claim ("calcium is needed for the maintenance of normal bones"). Vitamin K contributes another ("vitamin K contributes to the maintenance of normal bones"). Vitamin C contributes to normal collagen formation for the normal function of bones. The Register treats each nutrient separately, which is what compliant labelling has to do — but the picture they collectively describe is one of multiple nutrients with bone-relevant roles in normal physiology.
That doesn't tell anyone what they should take. It does explain why a multi-nutrient formulation containing D3, K2, calcium, and vitamin C exists at all.
Where Nutriluxe sits
The Nutriluxe Vitamin D3 4,000 IU + Vitamin K2 MK-7 with Calcium and Vitamin C uses cholecalciferol (D3) in a vegetarian-suitable form. It is one of four nutrients in the formulation that carry authorised claims relating to the maintenance of normal bones. Manufactured in the UK to GMP standards, in small batches, with a short ingredient list and no unnecessary fillers, coatings, or artificial additives.
For advice on the form and amount of vitamin D appropriate to your circumstances, speak to your GP, pharmacist, or registered healthcare professional. NHS guidance on vitamin D intake remains the starting point for most adults in the UK.
References
- NHS. Vitamin D. https://www.nhs.uk/conditions/vitamins-and-minerals/vitamin-d/
- Tripkovic L, Lambert H, Hart K, et al. Comparison of vitamin D2 and vitamin D3 supplementation in raising serum 25-hydroxyvitamin D status: a systematic review and meta-analysis. American Journal of Clinical Nutrition, 2012;95(6):1357–1364.
- Scientific Advisory Committee on Nutrition. Vitamin D and Health (2016). GOV.UK.
- Great Britain Nutrition and Health Claims Register. Department of Health and Social Care.
- British Nutrition Foundation. Vitamin D.
This article is for general information and educational purposes only. It does not constitute medical, nutritional, or professional health advice, and should not replace consultation with a qualified healthcare professional. Always speak to your GP, pharmacist, or a registered healthcare practitioner before starting any supplement, particularly if pregnant, breastfeeding, taking medication, or with an existing medical condition. Food supplements are not intended to diagnose, treat, cure, or prevent any disease, and are not a substitute for a varied and balanced diet and a healthy lifestyle. Do not exceed the recommended daily dose. Keep out of reach of young children. Health claims relate to the named nutrients as authorised on the Great Britain Nutrition and Health Claims Register. Information is accurate at the time of publication; guidance may change. Nutriluxe accepts no liability for any action taken on the basis of this content