Vitamin D2

vitamin

What is it

Vitamin D2, also called ergocalciferol, is a plant-derived form of vitamin D produced commercially by irradiating yeast or fungi. It is the form used in most prescription high-dose vitamin D and many vegan supplements.

How it works

Like D3, vitamin D2 is biologically inactive when absorbed. The liver hydroxylates it to 25-hydroxyvitamin D2, and the kidneys convert that to the active hormone 1,25-dihydroxyvitamin D2. Both bind the vitamin D receptor and support calcium absorption, bone mineralization, and immune function. The key difference from D3 is in how it behaves in the body. D2 binds less tightly to vitamin D binding protein and is cleared from the blood faster, so it tends to raise serum 25(OH)D levels less effectively at the same dose. For most clinical purposes the two forms are interchangeable, but D3 is generally preferred.

Evidence for 3 uses

AI-assisted evidence assessment — talk to your doctor before relying on any single supplement.

Treatment of vitamin D deficiency

Grade A

Strong evidence

High-dose D2 (typically 50,000 IU weekly) is a standard prescription regimen for correcting documented deficiency. It works, though D3 raises blood levels somewhat more reliably.

Bone health support

Grade B

Good evidence

D2 supports bone mineralization through the same mechanism as D3 by enabling calcium absorption. The bone-health evidence base is larger for D3.

Maintaining serum 25(OH)D levels

Grade B

Good evidence

D2 raises blood vitamin D levels but less effectively than D3 at the same dose, and the increase declines faster between doses. For long-term maintenance D3 is preferred.

Dosage

The RDA for total vitamin D is 600 IU (15 mcg) per day for adults up to age 70 and 800 IU (20 mcg) over 70. Prescription D2 is commonly given as 50,000 IU weekly for 8 to 12 weeks in people with documented deficiency, then a maintenance dose. Over-the-counter doses are typically 400 to 2,000 IU. The tolerable upper limit is 4,000 IU per day from all sources.

When and how to take it

Vitamin D2 is fat-soluble and absorbs best with a meal containing some dietary fat. Consistency is more important than time of day. Because vitamin D stores in body fat and liver, daily, weekly, or even monthly dosing can all be effective — choose what is easiest to maintain.

Food sources

Food	Amount	%DV
Mushrooms exposed to UV light, 1/2 cup	366 IU (9.2 mcg)	46%
Fortified plant milk, 1 cup	100 to 120 IU	15%

Safety

Vitamin D2 in typical doses is safe. Toxicity from long-term high-dose use can cause hypercalcemia with nausea, weakness, frequent urination, kidney stones, and in severe cases heart rhythm problems. Toxicity generally requires chronic intake well above 10,000 IU per day. Prescription 50,000 IU weekly dosing for documented deficiency is well tolerated short-term, but extended use without monitoring can push blood levels too high.

Who should be cautious

People with kidney disease, hyperparathyroidism, sarcoidosis, or other granulomatous diseases should not take vitamin D2 without medical guidance. Pregnant and breastfeeding women have the same RDA as other adults.

Interactions

Steroids reduce calcium absorption and impair vitamin D action. Orlistat and bile acid sequestrants reduce vitamin D absorption; take them several hours apart. Thiazide diuretics combined with high-dose vitamin D can raise calcium excessively. Certain anticonvulsants reduce vitamin D activity.

Frequently asked questions

Is D2 as effective as D3?⌄

Both raise vitamin D status, but D3 is generally more potent dose-for-dose. For most people D3 is the better choice unless they need a vegan or prescription option.

Why do doctors prescribe D2 instead of D3?⌄

Prescription D2 has been available longer in the U.S. in high-dose form (50,000 IU capsules), so many physicians default to it. High-dose D3 is increasingly available too.

Is vitamin D2 vegan?⌄

Yes. D2 is made from yeast or fungi exposed to UV light and is suitable for vegan diets.

How often do I take prescription 50,000 IU D2?⌄

Most regimens are once weekly for 8 to 12 weeks to correct deficiency, then a lower maintenance dose. Follow your prescriber's instructions and get blood levels rechecked.

References

NIH ODS Vitamin D Health Professional Fact Sheet — NIH Office of Dietary Supplements link

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Disclaimer: These statements have not been evaluated by the FDA. This page is educational, not a substitute for personalized medical advice. Evidence grades are AI-assisted assessments — talk to your doctor before starting any new supplement, especially if you're pregnant, breastfeeding, on medications, or managing a chronic condition.