Vitamin D3 vs. D2: Which Form Should You Choose?

Vitamin D2 and vitamin D3 look almost identical on a label. Both are called "vitamin D," both come in similar doses, and both raise your vitamin D levels. So does the form actually matter?

For most over-the-counter buyers, D3 is the more practical default — but D2 is not useless. The difference comes down to how long each form keeps blood levels up, where it comes from, and what dose you need.

What D2 and D3 actually are

Vitamin D helps your body absorb calcium and maintain normal bone mineralization. The vitamin from sun, food, or supplements is first converted by the liver to 25-hydroxyvitamin D [25(OH)D], then by the kidneys to the active form. A "vitamin D level" usually means blood 25(OH)D.

Per the NIH Office of Dietary Supplements, the two forms differ only in their chemical side chains. D2 (ergocalciferol) is made by irradiating ergosterol in yeast and is also found in UV-exposed mushrooms; it is the form most often used in prescription-strength products. D3 (cholecalciferol) is the form your skin makes from sunlight, typically made in supplements from lanolin from sheep's wool — though a lichen-based, animal-free version is also available.

A standard D3 capsule is not vegan, while D2 and lichen-based D3 can be — so check the source on the label if animal-free matters to you.

What the research says about blood levels

Both forms raise blood 25(OH)D. The NIH states this plainly — and then adds the key nuance: research shows D3 increases serum 25(OH)D to a greater extent than D2 and can maintain those higher levels for longer.

Meta-analyses back that summary. Tripkovic and colleagues (American Journal of Clinical Nutrition, 2012) concluded that D3 is more effective than D2 at raising serum 25(OH)D. A later meta-analysis of daily-dosing trials by van den Heuvel and colleagues (Advances in Nutrition, 2023), covering 20 comparative studies, again found D3 superior — with daily-dose comparisons showing levels about 10.39 nmol/L (around 40%) lower in the D2 groups.

Three nuances: the gap shrinks with daily dosing, it lost significance in participants with a body mass index above 25 kg/m² in the 2023 analysis, and D2 may reduce circulating 25(OH)D3. None of this means D2 "doesn't work" — the NIH notes both forms seem equally able to cure rickets.

How much do you actually need?

Vitamin D is listed in both micrograms (mcg) and International Units (IU), and 1 mcg equals 40 IU. So 25 mcg is 1,000 IU, and 125 mcg is 5,000 IU. The NIH Recommended Dietary Allowances for healthy people, assuming minimal sun exposure, are 15 mcg (600 IU) per day for adults ages 19–70 and 20 mcg (800 IU) per day for adults over 70. The Tolerable Upper Intake Level (UL) for adults is 100 mcg (4,000 IU) per day from all sources combined.

The NIH notes blood levels of 50 nmol/L (20 ng/mL) or more are generally considered sufficient for most people, while levels below 30 nmol/L (12 ng/mL) are associated with deficiency risk — and only a blood test can tell you where you stand.

Why the UL matters: many products contain 5,000 IU per serving, above the adult UL of 4,000 IU per day from all sources. Clinicians sometimes recommend higher intakes for specific people, but 5,000 IU should not be a casual default dose. If you are considering a dose above the UL, or you take steroids, statins, or thiazide diuretics, talk with a clinician first.

When D2 still makes sense

• You were prescribed D2. Prescription-strength vitamin D in the United States is commonly ergocalciferol (D2). Do not swap it for over-the-counter D3 without asking your clinician first.
• You want a vegan option and lichen D3 is unavailable or too costly. D2 is made without animal ingredients.
• You only need a modest daily top-up. At low daily doses the D2–D3 gap is smaller, so a D2 product you will actually take consistently may serve you better than one you forget.

How to choose in four steps

1. Read the form, not just the front. Look for "cholecalciferol" (D3) or "ergocalciferol" (D2) in the Supplement Facts panel, plus the source (lanolin vs. lichen) if it matters to you.
2. Read the per-serving dose. Check whether the IU figure is per capsule, per tablet, or per spray.
3. Match the dose to your situation. For something close to the adult RDA, a 1,000 IU product is a more natural fit than a 5,000 IU one. If a clinician recommended a higher dose, follow that guidance.
4. Take it with food containing some fat. Because vitamin D is fat-soluble, the NIH notes it is best absorbed with a meal or snack that includes some fat.

Note: vitamin K2, sometimes sold with D3, is a separate nutrient — this article makes no claim that it makes D3 work better.

Four options at 52nourish, compared by serving

All four are active at 52nourish; prices checked October 30, 2026, and may change.

• Solgar Vitamin D3 5,000 IU — $59.98. A simple, high-potency D3: 1 capsule per serving, 240 servings. Note 5,000 IU is above the adult UL of 4,000 IU per day from all sources.
• DEVA Vegan Vitamin D2 2,400 IU — $43.98. The D2 option: 1 tablet provides 2,400 IU, with no animal ingredients.
• NATURELO Vegan D3 + K2 from Lichen — $35.04. A vegan D3: 1 capsule provides 125 mcg (5,000 IU) of lichen-based D3 plus 120 mcg of vitamin K2 as MK-7 — proof "vegan" need not mean "D2 only." Same above-UL caution applies.
• Garden of Life Vegan D3 Spray 1,000 IU — $18.20. The low-dose option: 1 spray delivers 1,000 IU of lichen-based D3 — closest to the adult RDA, and suited to people who dislike capsules.

The choice is form plus source plus dose plus format — and dose (1,000 vs. 2,400 vs. 5,000 IU) may matter more to your routine than form alone.

The bottom line

If you are choosing freely and want the form most likely to raise and sustain blood 25(OH)D levels, the evidence points to D3. If you are vegan, D3 from lichen gives you that form without animal ingredients. If you were prescribed D2, or you prefer D2 for cost or availability, D2 still raises vitamin D levels — just, on average, less and for a shorter time than the same dose of D3.

Whatever you choose, read the per-serving dose and take it with a meal containing some fat. When in doubt — especially above 4,000 IU per day — ask a clinician rather than guessing from a label.

This article is for informational purposes only and is not medical advice. Talk with a qualified healthcare professional about your vitamin D needs, testing, and dosing.

Sources: NIH Office of Dietary Supplements, Vitamin D Health Professional Fact Sheet; Tripkovic et al., American Journal of Clinical Nutrition, 2012; van den Heuvel et al., Advances in Nutrition, 2023.