What Is Vitamin D2 (Ergocalciferol)? The D2 vs D3 Trials, UK Facts

Vitamin D2, or ergocalciferol, is one of the two forms of vitamin D. It is made from fungi and UV-treated yeast, and the body handles it as it handles vitamin D3: the liver and kidneys convert both to the same blood marker, 25-hydroxyvitamin D, and the same active hormone, calcitriol. The UK's Scientific Advisory Committee on Nutrition (SACN) concluded in 2024: "Both vitamin D2 and vitamin D3 increase blood 25(OH)D concentrations, and both forms prevent and treat vitamin D deficiency." Where daily-dose trials found a difference, D3 raised the marker by about 8 nmol/L more, a difference SACN said "may not be reliable".¹ The NHS: "All types of vitamin D work in this way."² The authorised wordings belong to the nutrient in either form: vitamin D contributes to the maintenance of normal bones, teeth and muscle function and to the normal function of the immune system. Part of the vitamin D guide.

What is vitamin D2, and what does "calciferol" mean?

Ergocalciferol is the vitamin D that fungi and yeast make when ultraviolet light strikes ergosterol. D3 (colecalciferol) is the animal form, made in skin and "primarily derived from lanolin extracted from sheep wool", while "Vegan vitamin D3 can be obtained from lichen."¹ "Calciferol" is the umbrella word, and on a UK prescription it means either: the BNF states that "when calciferol is prescribed or demanded, colecalciferol or ergocalciferol should be dispensed or supplied", and that "Ergocalciferol 400 units is equivalent to 10 micrograms".³ So calciferol tablets are vitamin D tablets, and "calciferol, mushroom origin" on a label is D2.

Does vitamin D2 raise your vitamin D as well as D3?

Both raise it; the size of any gap depended on how the dose was given. SACN's 2024 review: both forms "prevent and treat vitamin D deficiency", the pooled difference "may not be reliable", and in daily studies at 5 to 25 µg it read "an advantage of vitamin D3 over D2 in raising blood 25(OH)D concentration of about 8nmol per litre".¹ A 2012 meta-analysis of head-to-head trials found a D3 advantage "when given as a bolus dose", a single large dose, "but the effect was lost with daily supplementation".⁴ The daily-dose trials, as found:

A 2024 meta-analysis of daily and twice-weekly dosing put the gap across 12 daily comparisons at 10.39 nmol/L less for D2, found "a similar positive impact" of each form on its own 25-hydroxy metabolite, and reported the difference "lost significance predominantly in subjects with a BMI >25"; its first author is employed by a mushroom producer.⁹ When one form is taken the other form's metabolite falls, and a 2019 trial of 97 volunteers found this runs in both directions, "suggesting a common regulatory mechanism".¹⁰ And 25(OH)D2 cleared slightly faster than 25(OH)D3 in a tracer study, 13.9 against 15.1 days; in the 18 UK men alone, 15.1 against 15.6 days, not a significant difference.¹¹ What we don't know: whether the small daily-dose gap in the marker changes anything a person would notice. See also what vitamin D3 is good for.

Why do some people get prescribed D2 rather than D3?

NICE's clinical knowledge summary advises that "oral vitamin D3 is the vitamin D preparation of choice for the treatment of vitamin D deficiency, and vitamin D2 is an alternative option in some clinical situations", and that D2 "can be used in people who cannot take vitamin D3 for cultural, dietary, or religious reasons because of the animal sourcing of vitamin D, or the use of gelatine in some preparations".¹² The NHS notes D3 capsules "may contain an animal product called gelatine".² If your GP has prescribed ergocalciferol, the dose and the course are theirs to set; the question for them is whether the preparation suits your diet and level.¹² D2 is both a licensed medicine and a food-supplement ingredient.³

Which foods contain vitamin D2?

UV-exposed mushrooms are the one substantial unfortified source, holding more than 10 µg of D2 per 100 g if eaten before the best-before date, "higher than the level in most vitamin D-containing foods".¹³ Fortified foods such as some fat spreads and breakfast cereals may carry either form.¹⁴ Are mushrooms high in vitamin D has portions, and what foods are highest in vitamin D the full UK list.

What happens if you take vitamin D2 every day, and when should you take it?

The NHS figures apply to any form: 10 micrograms a day from October to March for everyone, all year for people who get little sun, "10 micrograms a day will be enough for most people", and "Do not take more than 100 micrograms (4,000 IU) of vitamin D a day as it could be harmful."¹⁴ Every product with vitamin D counts towards that ceiling: "Do not take any other vitamin or mineral supplements that contain calcium or vitamin D without talking to your doctor first."¹⁵ The NHS says to take tablets or capsules "with your main meal of the day"; we found no trial comparing morning with evening dosing of either form.¹⁵ In a 2012 comparison of 170 samples, every automated 25(OH)D immunoassay counted D2 and D3 together "with the exception of" one that measured D3 only, so if you take D2, ask whether your test measures total 25(OH)D.¹⁶ See the best time to take vitamin D, can you take too much vitamin D and how to check your vitamin D levels.

Who should not take vitamin D2?

No UK source we read carries a caution specific to D2; the NHS list for any vitamin D applies. Tell your doctor before starting if you have hypercalcaemia, hypercalciuria, kidney problems or a history of kidney stones, hypervitaminosis D, sarcoidosis or calcification, or a peanut or soya allergy.² On medicines, tell your doctor if you take digoxin or diuretics such as bendroflumethiazide or indapamide ("you may get too much calcium in your blood"), epilepsy medicines such as phenytoin, carbamazepine, phenobarbital or primidone ("you may need a larger dose") or steroids such as prednisolone; the NHS also names paraffin oil, cholestyramine, ketoconazole, clotrimazole and actinomycin.¹⁵ Nothing we read suggests D2 is harder on the kidneys than D3; ask a pharmacist. What you should not take with vitamin D carries the full list.

Frequently asked questions

What are the signs of vitamin D2 deficiency?

There is no separate D2 deficiency: deficiency is a low 25(OH)D from any cause, and the NHS describes bone pain and the bone changes of rickets and osteomalacia.¹⁴ Signs of vitamin D deficiency gives the NHS list.

How long does ergocalciferol take to work, and how does it make you feel?

Not straight away: the NHS explains that vitamin D must first be converted to calcitriol, that higher prescribed doses "work more quickly", and that bone, muscle or joint pain is "likely to get better when your vitamin D levels are normal again", "usually after a few weeks or months".² The 25-hydroxy form of D2 has a half-life of about two weeks, so levels build over weeks.¹¹ Nothing in the trials describes a feeling from D2 itself.

Does vitamin D2 help you sleep or give you energy?

No trial of D2 has measured either, and vitamin D has no authorised wording for sleep, energy, tiredness, mood, weight or joints in any form.¹⁷ Does low vitamin D affect sleep has the vitamin D sleep studies.

Can I take vitamin D2 rather than D3?

Both raise 25(OH)D and, in SACN's words, "both forms prevent and treat vitamin D deficiency"; the NHS says "All types of vitamin D work in this way."^{1, 2} At daily doses the average gap was about 8 to 10 nmol/L in D3's favour, which SACN said "may not be reliable".^{1, 9} The choice is diet, availability and, for a prescribed course, your prescriber's call.

Is vitamin D2 vegan?

Yes when made from UV-treated yeast or fungi; lichen D3 is the other vegan option and the same molecule as animal D3.¹ Which vitamin D is best for vegans sets out both; the vitamins and minerals guide covers the series.

Sources

1. SACN. Fortifying foods and drinks with vitamin D, 2024: summary; main report, section 2.6. gov.uk; gov.uk.
2. NHS. Colecalciferol: common questions; who can and cannot take it. nhs.uk; nhs.uk.
3. British National Formulary. Ergocalciferol. bnf.nice.org.uk.
4. Tripkovic L, et al. Comparison of vitamin D2 and vitamin D3 supplementation in raising serum 25-hydroxyvitamin D: systematic review and meta-analysis. American Journal of Clinical Nutrition, 2012. PubMed 22552031.
5. Holick MF, et al. Vitamin D2 is as effective as vitamin D3 in maintaining circulating concentrations of 25-hydroxyvitamin D. Journal of Clinical Endocrinology and Metabolism, 2008. PubMed 18089691.
6. Fisk CM, et al. Fortified malted milk drinks containing low-dose ergocalciferol and cholecalciferol do not differ in raising serum 25-hydroxyvitamin D. Journal of Nutrition, 2012. PubMed 22623396.
7. Tripkovic L, et al. Daily supplementation with 15 μg vitamin D2 compared with vitamin D3 to increase wintertime 25-hydroxyvitamin D status. American Journal of Clinical Nutrition, 2017. PubMed 28679555.
8. Logan VF, et al. British Journal of Nutrition, 2013. PubMed 23168298.
9. van den Heuvel EG, et al. Comparison of the effect of daily vitamin D2 and vitamin D3 supplementation on serum 25-hydroxyvitamin D concentration. Advances in Nutrition, 2024. PubMed 37865222.
10. Hammami MM, et al. Vitamin-D2 treatment-associated decrease in 25(OH)D3 level is a reciprocal phenomenon. BMC Endocrine Disorders, 2019. PubMed 30658603.
11. Jones KS, et al. 25(OH)D2 half-life is shorter than 25(OH)D3 half-life. Journal of Clinical Endocrinology and Metabolism, 2014. PubMed 24885631.
12. NICE CKS. Vitamin D deficiency in adults: management; prescribing information. cks.nice.org.uk; cks.nice.org.uk.
13. Cardwell G, et al. A review of mushrooms as a potential source of dietary vitamin D. Nutrients, 2018. PubMed 30322118.
14. NHS. Vitamin D. nhs.uk.
15. NHS. Colecalciferol: how and when to take it; taking it with other medicines. nhs.uk; nhs.uk.
16. Farrell CJ, et al. State-of-the-art vitamin D assays. Clinical Chemistry, 2012. PubMed 22230812.
17. Great Britain nutrition and health claims register. gov.uk.

This article is general information, not medical advice. Take prescribed ergocalciferol as your prescriber set it, and ask a pharmacist before adding any product containing vitamin D or calcium.