The plant and fungal form of vitamin D, produced commercially by ultraviolet irradiation of ergosterol from yeast. It is the vitamin D in most prescription high-dose capsules in the United States and in many fortified plant milks.
D2 and D3 are not equivalent, and the difference has been measured rather than assumed: head-to-head trials and a meta-analysis of them find D3 raises and maintains blood 25-hydroxyvitamin D more effectively than an equal dose of D2, particularly with intermittent dosing. D2 still works — it corrects deficiency, and it is the form used in the trials that ended nutritional rickets as a common childhood disease — but more of it is needed for the same blood level. Its practical niches are veganism, where lichen-derived D3 is the alternative, and prescription repletion, where the 50,000 IU capsule format happens to be D2.
Sold as
Prescription 50,000 IU capsule, Tablet, Oral solution, Fortificant in plant milks and cereals
Also known as
Ergocalciferol, Plant vitamin D, Vegetarian vitamin D
Regulation: Available in the US as both a prescription drug (50,000 IU ergocalciferol) and an over-the-counter supplement. The 4,000 IU/day Tolerable Upper Intake Level set by the IOM covers total vitamin D from all forms combined, D2 and D3 together.
What the research used
The amounts, forms and durations published trials of Vitamin D2 (ergocalciferol) actually administered.
These are the amounts published trials administered — not a recommendation, and not a dose to copy. Trial participants were screened, supervised and given a characterised preparation. What is in a retail bottle is frequently not what was studied, and the amount that suits one person is not general advice.
Studied for Prescription repletion of documented deficiency
50000 IU
Moderate
Capsule, weekly · 8–12 weeks
The standard US repletion format, used with blood monitoring. The same total exposure given as daily D3 raises 25-hydroxyvitamin D more reliably in comparative trials.
Studied for Everyday supplementation
400–2000 IU
Moderate
Tablet or fortified food
Against the 600–800 IU/day RDA. Because D2 is less potent per IU at maintaining blood levels, the same number on a D2 label and a D3 label do not deliver the same result.
Studied for Tolerable Upper Intake Level, adults
4000 IU
Strong
Applies to total vitamin D intake from supplements in any form.
This is general information about food, not medical advice. It cannot diagnose, treat or replace guidance from a clinician who knows your history.
When it was taken
Each window says whether a trial compared it against an alternative, or whether it is convention and pharmacology. Most timing advice is the second kind.
Each timing below was actually compared against an alternative in a trial, which is unusual.
🍽️With food
Limited
Fat-soluble and better absorbed with a meal containing fat, as with D3. Absorption studies support this; no trial has compared D2 timings specifically.
Timing was tested. A trial compared this window against another and reported a difference.
The evidence in depth
Best supported: Moderate
What each association actually rests on, and the papers behind it. A rating describes the state of the research, not how promising the supplement sounds. How we rate evidence.
D2 corrects vitamin D deficiency and the bone disease it causes, which is why it was the form used in the classic rickets work. For maintaining a given blood level it is less efficient than D3, so trials comparing bone outcomes between the two forms are the open question rather than whether it works at all.
Moderate evidence. Several human studies point the same way, with real caveats.
Evidence is limited for vitamin D2 and fatigue or energy in people who are not deficient. Where fatigue improves it is in the context of correcting an established deficiency, which says nothing about supplementing on an adequate intake.
Not enough evidence. Not enough human research to say anything useful yet.
Systematic review · The Cochrane database of systematic reviews · 2023 · PMID 36705288
Deep research mode adds each paper’s own conclusion and stated limitations.
Things to know
Interactions, contraindications and dose limits, most serious first. Concentrated extracts interact with medication in ways the whole plant does not, so this section carries more weight here than it does on a food page.
Too much
Same toxicity profile as D3
Sustained excess causes hypercalcaemia — thirst, frequent urination, nausea, confusion, kidney stones and soft-tissue calcification. The high-strength 50,000 IU format makes dosing-frequency errors consequential: weekly and daily are not interchangeable, and mistakes of this kind account for several published toxicity cases.
Worth knowing
Not for unsupervised use in granulomatous disease or hypercalcaemia
Sarcoidosis, tuberculosis and some lymphomas produce active vitamin D outside normal regulation, so supplementation risks hypercalcaemia. The same applies to primary hyperparathyroidism and advanced kidney disease.
Orlistat, cholestyramine and colestipol reduce absorption; phenytoin, carbamazepine, rifampicin and glucocorticoids speed its breakdown; thiazide diuretics and digoxin interact through calcium.
Worth knowing
Source matters for vegans, though not always the way labels suggest
D2 is reliably plant-derived, but D3 from lichen is equally vegan and more efficient at raising blood levels. D3 from lanolin is not vegan. Labels rarely make the source explicit.
In the food catalogue
The whole-food form, where one exists. The evidence for a concentrated extract rarely transfers to the food, or the other way round — these are cross-links, not equivalents.