Vitamin D3 vs D2: Which Form Should You Take?

Walk down any supplement aisle and you’ll see “vitamin D3” on almost every bottle, while the high-dose capsules doctors prescribe are often vitamin D2. Both forms are used to prevent and correct low vitamin D, and both are converted by your liver into the same marker that blood tests measure. But they come from different sources, and they don’t behave identically in the body. This guide explains the difference, what the research shows, and how to choose.

For a broader look at dosing, testing and choosing a product, see our main vitamin D supplements guide.

What’s the difference between vitamin D3 and D2?

Vitamin D isn’t one compound but a small family. The two forms that matter for nutrition are:

• Vitamin D3 (cholecalciferol): the form your skin makes when it’s exposed to UVB sunlight. It’s also found naturally in oily fish, cod liver oil and egg yolks. Most supplements make D3 from lanolin, the oil in sheep’s wool, while vegan versions are made from lichen.
• Vitamin D2 (ergocalciferol): made by plants and fungi when they’re exposed to UV light. Supplements make it from yeast. Mushrooms grown under UV lamps, often labeled “high in vitamin D”, are a food source.

Both forms are inactive until your body processes them. The liver converts them into 25-hydroxyvitamin D, often written 25(OH)D, which is the form measured in a blood test. The kidneys then convert some of it into the active hormone that helps you absorb calcium and keep bones strong. The two forms differ slightly in chemical structure, and that small difference affects how long they last in the blood.

Vitamin D3 vs D2 compared

Based on the NIH Office of Dietary Supplements vitamin D fact sheet and the research summarized below.

Which raises vitamin D levels more?

Moderate evidence The best summary of the evidence is a 2012 systematic review and meta-analysis in the American Journal of Clinical Nutrition that pooled randomized trials comparing the two forms head to head.

That fits with an earlier trial from Boston University, in which 68 adults took 1,000 IU a day of D2, D3 or a combination for 11 weeks. All three groups had similar increases in blood vitamin D, suggesting that at a normal daily dose, D2 works about as well (Holick et al., 2008).

Why would D3 do better with large doses? Researchers think the body breaks D2 down a little faster, and that D3’s main circulating form binds more strongly to the protein that carries vitamin D in the blood, so it hangs around longer. With a small dose every day, that faster turnover matters less because you’re constantly topping up.

It’s also worth remembering what these studies measure: blood levels, not health outcomes. There’s no good evidence that one form protects bones or lowers disease risk better than the other once your vitamin D status is adequate. Large trials such as VITAL, which gave healthy adults 2,000 IU of D3 a day, found no reduction in fractures, heart disease or cancer in people who weren’t deficient to begin with.

Vegan and vegetarian options

Standard vitamin D3 comes from lanolin, which is collected from sheep’s wool without harming the animal. It’s suitable for most vegetarians but not for vegans. If you’re vegan, you have two good choices:

• Lichen-based D3: lichen is a combination of fungi and algae that makes vitamin D3. Look for “vegan D3” or “from lichen” and a certified vegan logo on the label.
• Vitamin D2: always plant- or yeast-based. It’s a sensible choice for daily dosing, given that the research shows little difference at around 1,000 IU a day.

Also check the capsule. Softgels are often made from gelatin, which isn’t vegetarian. Some plant milks and breakfast cereals are fortified with D2 or vegan D3; the ingredients list will say which.

Prescription vitamin D2 (50,000 IU)

In the US, the most common prescription vitamin D is ergocalciferol in 50,000 IU capsules, often taken once a week for 8 to 12 weeks to correct a confirmed deficiency. It’s been used for decades and is effective. Because D3 holds blood levels better with intermittent dosing, some doctors prefer high-dose D3 instead, and both are reasonable options.

If you’ve been prescribed high-dose vitamin D, take it exactly as directed and don’t add extra supplements on top without checking. These doses are far above the daily upper limit and are only safe for a set period under medical supervision, usually with a follow-up blood test.

How much vitamin D do you need?

The Recommended Dietary Allowances apply to both forms. Labels may list amounts in micrograms (mcg), international units (IU) or both; 1 mcg equals 40 IU.

*Adequate Intake for infants. Source: NIH Office of Dietary Supplements, Vitamin D fact sheet for health professionals.

Supplements of 1,000 to 2,000 IU a day are common and safe for most adults. Products with 5,000 or 10,000 IU per capsule exceed the upper limit and should only be used if a doctor recommends them. Vitamin D is fat-soluble, so taking it with a meal that contains some fat may help absorption.

Safety and interactions

Both forms are safe at recommended doses. Too much vitamin D over time, almost always from high-dose supplements rather than sunlight or food, can raise blood calcium levels.

Which should you choose?

Choose vitamin D3 if you:

• Want the form with the strongest evidence for raising blood levels.
• Plan to take a larger dose once a week rather than every day.
• Want the widest choice of products and prices.

Choose vitamin D2 if you:

• Are vegan and can’t find or afford lichen-based D3.
• Have been prescribed it by your doctor.
• Take a modest daily dose, where it performs about as well as D3.

Whichever form you pick, choose a product with a third-party testing seal such as USP Verified or NSF Certified, which confirms the dose on the label matches what’s inside. If you’re also low in other nutrients, our guides to magnesium-rich foods and fish oil supplements may be useful.

Related on Pure Nutrition Facts: our guide to whether you need a multivitamin.

Vitamin D3 vs D2 FAQ