Vitamin D3 (cholecalciferol) is the form most supplement shelves, and most researchers, lean toward, and vitamin D2 (ergocalciferol) is the plant and fungal form that still shows up in some prescription products and fortified foods. Our verdict after reading the labels and the research: D3 is the safer default to look for on a standard over-the-counter product, mainly because several published trials and reviews found it raises blood levels of 25-hydroxyvitamin D more effectively than D2. That is a finding about blood markers, not a promise about health outcomes, and which form suits you is a question for your doctor.
This is a research-based comparison, not a product test. We did not take either form and measure anything on ourselves, and nothing here tells you what to take. We bought bottles of both types at full retail, read the Supplement Facts panels, checked for third-party seals, and compared the labels against the published literature. If your doctor has prescribed one form, that decision outranks this article.
What D2 and D3 Actually Are
Both are forms of vitamin D that the body converts, first in the liver and then in the kidneys, into the active hormone. The NIH Office of Dietary Supplements fact sheet on vitamin D describes D2 as made by irradiating ergosterol from yeast or mushrooms and D3 as made in skin on sun exposure, found in some animal foods, and produced for supplements usually from lanolin, the oil in sheep wool. A third source, lichen, gives vegan D3. The label will say "vitamin D2 (ergocalciferol)" or "vitamin D3 (cholecalciferol)", so the form is easy to find once you know to look.
What the Research Says About Blood Levels
The most-cited head-to-head work looks at serum 25-hydroxyvitamin D, the standard blood marker. A 2012 systematic review and meta-analysis by Tripkovic and colleagues in the American Journal of Clinical Nutrition concluded that D3 was more effective than D2 at raising that marker. An earlier paper by Armas and colleagues in the Journal of Clinical Endocrinology and Metabolism (2004) found D2 had much lower potency than D3 in a trial using a single large dose, and Houghton and Vieth argued in the American Journal of Clinical Nutrition in 2006 against D2 as a supplement. A caveat matters here: the studies differ in dose, schedule and population, and a higher blood marker is not the same as a better health result. Evidence that one form prevents or treats any condition better than the other is thin, and we do not claim it.
Vitamin D2 Versus D3 at a Glance
| Factor | Vitamin D2 (ergocalciferol) | Vitamin D3 (cholecalciferol) |
|---|---|---|
| Typical source | Irradiated yeast or mushrooms | Lanolin, or lichen for vegan versions |
| Vegan friendly | Yes, in most products | Only lichen-based versions |
| Blood level evidence | Lower rise in the Tripkovic 2012 review | Greater rise in the same review |
| Where you find it | Some prescription products, fortified foods | Most over-the-counter supplements |
| Third-party seals to look for | USP Verified, NSF Certified | USP Verified, NSF Certified |
| Price | Usually similar (verify current pricing) | Usually similar (verify current pricing) |
Neither form is exotic or expensive, and the price gap between them on the shelves we checked was small, so cost rarely settles the choice. The practical decision comes down to diet, your doctor's guidance, and whether the product is independently tested.
How We Compared the Labels
We bought a spread of D2 and D3 products at full price, with no press samples, and read each Supplement Facts panel for the form, the amount per serving, the other ingredients and any added calcium or vitamin K. We looked for USP Verified or NSF seals and treated an unverifiable seal claim as no seal. We did not run lab tests ourselves. Our broader approach to supplement testing is in the best supplements guide, and the supplement label guide explains what each part of the panel means. Where we could not confirm a claim against a primary source we left it out.
Who Might Prefer D2 and Who Might Prefer D3
A person who avoids all animal-derived ingredients has two routes: a D2 product, or a lichen-sourced D3 product, which exists but costs more and is not on every shelf. Someone who simply wants the form with the stronger blood-level evidence will find that most standard products are D3. In the United States, prescription vitamin D at high strength has historically been D2, so if a clinician has handed you a prescription, do not swap it for an over-the-counter bottle on your own. Our guide on the best vitamin D supplements covers specific products.
Safety, Interactions and Who Should Ask a Doctor First
Vitamin D is fat soluble, so it builds up, and the NIH fact sheet sets a tolerable upper intake level for adults. Too much can raise blood calcium, which can cause real problems, so a total from all sources, including a multivitamin, is worth knowing. The same fact sheet notes that some medicines interact, including certain steroids such as prednisone, the weight-loss drug orlistat, cholesterol medicines such as statins in some cases, and thiazide diuretics, which can raise calcium. People with kidney disease, sarcoidosis, a history of high calcium or kidney stones, and anyone who is pregnant or breastfeeding should talk to a doctor before using either form. A blood test, not a guess, is how clinicians decide whether you need any at all, which our blood tests before supplements guide explains.
Why Third-Party Testing Matters More Than the Form
Supplements in the US are not approved before sale, so the amount on the front of the bottle is the maker's claim. A seal from USP or NSF means an outside lab checked that the contents match the label and screened for contaminants, which is a stronger signal of quality than D2 versus D3. See USP vs NSF certification for how the two programs differ, and third-party testing explained for the basics.
Where the Evidence Is Still Thin
It helps to be plain about what the research does not show. Most of the comparisons we found measure a blood marker over weeks, not whether anyone had fewer fractures, better bone density or any other outcome. Doses, schedules, baseline levels and participant groups differ between trials, and some used a single large dose rather than daily amounts, which does not reflect how most people use a supplement. Some researchers also note that D2 may behave differently depending on the dosing pattern. For that reason we describe D3 as the form with the stronger blood-level evidence and stop there. We do not say either form protects against anything, and we would not trust a label or an advertisement that does. Your own results depend on diet, sun exposure, skin tone, body size, age and health conditions, which is why a clinician looking at your blood work is better placed to advise you than a general article. If you are comparing brands rather than forms, our guide to supplement marketing red flags is a useful next read.
The bottom line: for a standard over-the-counter product, look for D3 with a USP or NSF seal, choose lichen-sourced D3 or D2 if you avoid animal products, and let your doctor decide on any prescription form.
