Vitamin D3 (cholecalciferol) raises and maintains blood levels of vitamin D more effectively than D2 (ergocalciferol). For daily supplementing, D3 is the better choice.
Two forms. One word on the label. Most people never notice which one they're buying.
They should. The difference shows up in your blood, not on the front of the box. Here's what separates them, and what to look for.
WHERE THEY COME FROM
D3 is the form your body makes when sunlight hits your skin. It's also the form in animal-based foods, and the vegan versions made from lichen. D2 comes from plants and fungi, usually UV-treated yeast or mushrooms. It's cheaper to produce, which is why it still turns up in some fortified foods and high-dose prescriptions.
Same vitamin family. Different molecule. And your body doesn't treat the two the same way.
WHAT THE RESEARCH SHOWS
D3 wins on the measure that counts: raising serum 25(OH)D, the marker used to gauge your status. A 2012 meta-analysis in The American Journal of Clinical Nutrition pooled randomized trials that compared the two head to head and found D3 significantly more effective at raising 25(OH)D levels.
Newer work points the same way. A 2025 systematic review in Nutrition Reviews found that taking D2 was associated with a measurable drop in the D3 already circulating in the blood. The mechanism behind that is still debated, and some of it likely comes down to clearance rather than D2 working against D3 directly. Either way, the practical answer lands in the same place.
WHY D3 HOLDS BETTER
The main reason is how long each form lasts. A stable-isotope study in The Journal of Clinical Endocrinology & Metabolism measured the half-lives directly and found that 25(OH)D2 clears from the blood faster than 25(OH)D3.
Faster clearance means D2 fades sooner between doses. Researchers note that taking it daily can partly close the gap, but D3 is still the more reliable way to get your levels up and keep them there.
HOW TO SPOT IT ON A LABEL
This is the easy part. Flip the bottle and read the form:
- Cholecalciferol is vitamin D3. This is the one you want.
- Ergocalciferol is vitamin D2. The weaker form.
If a product only says "vitamin D" and never names the form, treat that as a reason to be skeptical of the whole label. D3X uses D3, listed plainly as cholecalciferol.
WHAT IT MEANS FOR YOU
If you're taking vitamin D to actually move your levels, the form is not a technicality. D3 is what your body makes from sunlight, it raises 25(OH)D more effectively, and it lasts longer between doses. D2 isn't useless, but it's the weaker tool, and there's little reason to pick it when D3 is sitting right next to it.
One word on a label. Get it right.
Cholecalciferol, not ergocalciferol. That's the whole game.
Sources
Tripkovic L, et al. "Comparison of vitamin D2 and vitamin D3 supplementation in raising serum 25-hydroxyvitamin D status: a systematic review and meta-analysis." The American Journal of Clinical Nutrition, 2012.
Brown E, et al. "Effect of Vitamin D2 Supplementation on 25-Hydroxyvitamin D3 Status: A Systematic Review and Meta-Analysis of Randomized Controlled Trials." Nutrition Reviews, 2025.
Jones KS, et al. "25(OH)D2 Half-Life Is Shorter Than 25(OH)D3 Half-Life and Is Influenced by DBP Concentration and Genotype." The Journal of Clinical Endocrinology & Metabolism, 2014.
Frequently Asked
Is vitamin D3 or D2 better?
Vitamin D3 (cholecalciferol) raises and maintains blood levels of vitamin D more effectively than D2 (ergocalciferol), according to a 2012 meta-analysis in The American Journal of Clinical Nutrition. D3 is also the form your body makes from sunlight.
What is the difference between cholecalciferol and ergocalciferol?
Cholecalciferol is vitamin D3, the form made in skin from sunlight and found in animal sources and lichen. Ergocalciferol is vitamin D2, made from plants and fungi. D3 raises serum 25(OH)D more effectively and lasts longer in the body.
Why does vitamin D2 not work as well as D3?
The main reason is half-life. A stable-isotope study found that 25(OH)D2 clears from the blood faster than 25(OH)D3, so D2 fades sooner between doses. That makes D3 the more reliable way to raise and hold vitamin D levels.
How do I know if my supplement is D3 or D2?
Read the form on the label. Cholecalciferol means vitamin D3, the form to choose. Ergocalciferol means vitamin D2. If the label only says 'vitamin D' with no form listed, treat that as a red flag.