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.
| Vitamin D2 | Vitamin D3 | |
|---|---|---|
| Label name | Ergocalciferol | Cholecalciferol |
| Source | Plants and fungi, UV-treated yeast or mushrooms | Sunlight on skin, animal foods, lichen |
| Raising 25(OH)D | Less effective | More effective |
| Half-life | Shorter, clears faster | Longer, holds between doses |
| Best for daily use | No | Yes |
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.
A more recent systematic review and meta-analysis in Advances in Nutrition, covering 20 clinical trials, put a number on the gap: daily supplementation with D2 produced roughly a 40% lower increase in total 25(OH)D than the same approach with D3, an average difference of about 4.12 ng/mL.
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.
THE FORM IS ONLY HALF OF IT
Picking D3 gets you the right molecule. It does not settle whether your body absorbs it well.
Vitamin D is fat-soluble, which means it needs fat present to be absorbed properly. A D3 tablet taken dry on an empty stomach is the right form delivered badly. That is why the carrier matters alongside the label: vitamin D needs fat to be absorbed, and the format you choose determines whether that happens by default or by luck. The same logic applies to liquid versus capsule.
Cholecalciferol on the label, and something oily in the bottle. Both, not either.
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.
"Comparative Efficacy of Vitamin D2 and Vitamin D3 Supplementation in Improving Vitamin D Status: A Systematic Review and Meta-analysis." Advances in Nutrition, 2024.
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.
