D3 is 87% more potent at raising serum vitamin D and holds blood levels longer, per a 2012 meta-analysis. D2 is naturally vegan and remains a common prescription form. D3 does the job at lower doses; D2 does the same job at higher ones.
| Vitamin D2 (Ergocalciferol) | Vitamin D3 (Cholecalciferol) | |
|---|---|---|
| Potency per dose | Needs higher doses | 87% more potent (2012 meta-analysis) |
| Duration in body | Shorter half-life | Longer half-life |
| Source | Fungi, plants | Lanolin, fish, or lichen |
| Vegan options | Naturally vegan | Lichen-derived available |
| Research | Smaller trial base | Larger trial base |
Vitamin D comes in two main forms: D2 (ergocalciferol) and D3 (cholecalciferol). While both can raise vitamin D levels, they're not equally effective. Here's what you need to know.
The Key Difference
D3 is what your skin produces when exposed to sunlight. D2 is made by fungi exposed to UV light. Your body handles them differently.
A 2012 meta-analysis found D3 is 87% more potent at raising and maintaining serum 25-hydroxyvitamin D levels. You'd need almost twice as much D2 to get the same effect as D3.
Where the Potency Difference Comes From
Binding affinity: D3 binds more strongly to vitamin D-binding protein in your blood, so it circulates longer.
Metabolism: Your liver converts D3 to 25-hydroxyvitamin D more efficiently.
Half-life: D3 stays in your system longer, maintaining steadier blood levels between doses.
When D2 Makes Sense
The main advantage of D2 is that it's naturally vegan. If you follow a strict plant-based diet and can't find lichen-derived D3 (which is vegan), D2 is a reasonable alternative. You may just need higher doses.
Some prescription vitamin D is D2, typically in 50,000 IU doses for treating severe deficiency. This works, though many doctors now prefer D3.
Dosing Considerations
If using D3: 2,000-5,000 IU daily is typical for maintenance.
If using D2: You may need 50-87% higher doses to achieve similar results.
Both should be taken with food containing fat for proper absorption. Get your levels tested to dial in your dose.
D3 raises and holds blood levels more efficiently and carries the deeper research base, and lichen-derived versions cover the vegan case. D2 does the same job at higher doses. Match the form to your constraint and test your levels either way.
Educational reading, not medical advice. Your doctor makes the call for your body.
Written and reviewed by the IngredientMD editorial team.