Vitamin D2 (Ergocalciferol): Uses, Benefits, Dosage & Safety
Last updated: August 2026 · Reviewed by the FactoWiki Editorial Team for clarity and source accuracy
Quick summary
Vitamin D2 comes from plant and fungal sources and is the standard vegan option. It does raise vitamin D levels, but less effectively than D3 and with a shorter duration — so if you use it, more frequent or higher dosing is warranted.
What is Vitamin D2 (Ergocalciferol)?
Ergocalciferol, produced by UV irradiation of ergosterol in yeast and fungi. UV-exposed mushrooms are the main food source. It is the form used in some high-dose prescription preparations and the traditional vegan supplement, though vegan D3 from lichen now exists.
What Vitamin D2 (Ergocalciferol) is commonly used for
Correcting deficiency in people avoiding animal-derived products, and in some high-dose prescription regimens.
How Vitamin D2 (Ergocalciferol) works
D2 follows the same activation pathway as D3 — liver hydroxylation then kidney activation — and binds the same receptor. The difference is pharmacokinetic: D2 has lower affinity for vitamin D binding protein, is cleared faster, and produces a smaller and less sustained rise in 25(OH)D per unit dose.
What the evidence says
Each claim below is tied to the specific study behind it, rather than to a general reading list.
- D3 raised serum 25(OH)D more effectively than D2 in a systematic review and meta-analysis. Tripkovic et al., American Journal of Clinical Nutrition, 2012 — systematic review and meta-analysis. (PMID 22552031)
- D2 has lower binding affinity for vitamin D binding protein and faster clearance. Houghton & Vieth, American Journal of Clinical Nutrition, 2006 — review of the case against D2. (PubMed)
- UV-exposed mushrooms are a dietary source of vitamin D2. Cardwell et al., Nutrients, 2018 — review of vitamin D in mushrooms. (PubMed)
Typical dosage used in studies
Where D2 is used, larger or more frequent doses are needed for the same effect as D3. Weekly high-dose D2 is a common prescription pattern. Take with a fat-containing meal.
Side effects and safety
Toxicity risk is the same as D3 at equivalent effective exposure — sustained excess causes hypercalcaemia. The same 4,000 IU upper limit applies.
Medication interactions and who should avoid Vitamin D2 (Ergocalciferol)
Medication & safety check
Same interactions as D3: thiazides, corticosteroids, orlistat, cholestyramine and certain anticonvulsants. Caution in granulomatous disease.
General information, not personal medical advice. If you take any medication, confirm it is safe to combine with Vitamin D2 (Ergocalciferol) with your doctor or pharmacist first.
Sources & further reading
The claim-level citations above are drawn from these sources:
- Tripkovic et al., American Journal of Clinical Nutrition, 2012 — systematic review and meta-analysis — PMID 22552031
- Houghton & Vieth, American Journal of Clinical Nutrition, 2006 — review of the case against D2 — find on PubMed
- Cardwell et al., Nutrients, 2018 — review of vitamin D in mushrooms — find on PubMed
- NIH Office of Dietary Supplements
- NIH National Center for Complementary and Integrative Health
Frequently asked questions
Is D2 useless?
No — it raises vitamin D levels and is used in prescription regimens. It is simply less efficient per unit dose than D3, so more is needed.
What should vegans take?
Lichen-derived D3 is now widely available and is the better option where the goal is efficient repletion. D2 remains a reasonable fallback.
Does the difference matter clinically?
At maintenance doses, modestly. For correcting a substantial deficiency, D3 gets there faster and holds levels better.
Part of a wider guide
Vitamin D2 (Ergocalciferol) is one form of Vitamin D. This page covers what is specific to this form — absorption, tolerability, dosing and who it suits. For the underlying nutrient itself, its overall evidence base and general safety, read the Vitamin D guide.
Where you'll find Vitamin D2 (Ergocalciferol)
Vitamin D2 (Ergocalciferol) appears in Vitamins formulas. Browse the supplement guides to see the products we review, each with a full breakdown of formula, pricing and safety.
Related ingredients to explore
Ingredients often studied or formulated alongside Vitamin D2 (Ergocalciferol).
General information, not medical advice.