Vitamin D supplements come in two main forms: D3 (cholecalciferol) and D2 (ergocalciferol). Best form of vitamin d for most people is D3 due to better effectiveness at raising blood levels.
D3 vs D2
Vitamin D3 (cholecalciferol):
- The form humans produce in skin from sun exposure
- Found in animal sources (fish, egg yolks)
- More effective at raising blood vitamin D levels
- Longer-lasting effects
- Available OTC widely
Vitamin D2 (ergocalciferol):
- Plant/fungal source
- Available as 50,000 IU prescription
- Less effective per IU than D3
- Vegan-friendly
Why D3 is generally preferred
- More effective at raising 25-OH-D levels
- More natural form
- Better bioavailability
- Available in convenient daily doses
For most patients, D3 1000-2000 IU daily is reasonable. Higher doses for documented deficiency.
Vitamin D with K2
K2 is sometimes co-administered:
- Theoretical role in directing calcium to bones rather than soft tissue
- Limited human outcome data
- Some products combine D3 + K2
- Not strictly necessary but reasonable
Frequently Asked Questions
Should I take D2 or D3?
D3 for most patients. D2 only if specifically prescribed (high-dose) or vegan.
Are vegan D3 supplements available?
Yes, from lichen sources. Look for plant-based D3.
Should I take D3 with K2?
Reasonable but not essential. Combination products available.
How much vitamin D should I take?
1000-2000 IU daily for most adults. More for deficiency.
Should I take vitamin D with food?
Yes. Fat-soluble — absorbs better with meals.
The bottom line on vitamin D forms
D3 generally preferred over D2. K2 reasonable adjunct but not essential. Take with food. See our vitamin D test guide.