Vitamin D3 (cholecalciferol) is the clear winner for supplementation. Multiple RCTs and meta-analyses confirm D3 raises serum 25(OH)D levels 87% more effectively than D2 at equivalent doses and sustains those levels for longer. D3 is the form naturally produced in human skin from sunlight.
Overview
Vitamin D3 and D2 are both used to treat and prevent vitamin D deficiency — but they are not equal. Multiple head-to-head trials show D3 is significantly more potent at raising and maintaining blood 25(OH)D levels. Here's why, and when D2 might still be appropriate.
What Is Vitamin D3 (Cholecalciferol)?
The form of vitamin D produced in human skin upon UVB exposure and found in animal-based foods. Converted in the liver to 25(OH)D3 (calcidiol) — the main circulating storage form — and then to the active form 1,25(OH)2D3 (calcitriol) in the kidneys.
Best for: All-round vitamin D supplementation, Deficiency correction, Immune function, Bone health.
Standard dose: 2,000–4,000 IU/day for most adults; take with fat-containing meal.
Side effects: Safe at recommended doses. Fat-soluble — excess stores in tissue. Toxicity at chronic doses >10,000 IU/day..
What Is Vitamin D2 (Ergocalciferol)?
Produced by UV irradiation of ergosterol in fungi and yeast. The historically dominant prescription form of vitamin D (Drisdol). Structurally similar to D3 but metabolised differently, resulting in lower potency and shorter duration of action.
Best for: Vegans requiring supplemental vitamin D (mushroom-derived D2 is plant-based), Prescription-only situations where D2 is specified by a physician, Countries where D3 from animal sources is not available.
Standard dose: Higher doses required to achieve equivalent effect to D3 (typically 2–3× the D3 dose).
Side effects: Same safety profile as D3. Toxicity risk at very high doses..
Evidence & Absorption Scores
We scored both on four dimensions: quality of clinical evidence, bioavailability, GI tolerance, and value for money. Scores are out of 10:
Head-to-Head Comparison
| Category | ▲ Vitamin D3 (Cholecalciferol) | ▲ Vitamin D2 (Ergocalciferol) |
|---|---|---|
| Potency at Equal Dose | 87% more effective at raising serum 25(OH)D | Less potent — requires higher dose for equivalence |
| Duration of Action | Half-life ~2 weeks — sustained levels | Half-life ~4 days — drops faster |
| Vegan Suitability | Not vegan (derived from lanolin/fish) | Vegan (mushroom/yeast derived) |
| Prescription Availability | OTC widely | Often the prescribed form |
| Clinical Evidence | Extensive — thousands of RCTs | Good — fewer studies but decades of clinical use |
| Immune Support | Superior | Adequate |
| Bone Health | Superior | Adequate |
| Cost | Very affordable | Similarly affordable OTC |
Best Uses for Each
✅ Vitamin D3 (Cholecalciferol) — Best For
- All-round vitamin D supplementation
- Deficiency correction
- Immune function
- Bone health
✅ Vitamin D2 (Ergocalciferol) — Best For
- Vegans requiring supplemental vitamin D (mushroom-derived D2 is plant-based)
- Prescription-only situations where D2 is specified by a physician
- Countries where D3 from animal sources is not available
Who Should Choose Vitamin D3 (Cholecalciferol)?
▲ Choose Vitamin if:
Almost everyone. D3 is the superior choice for efficacy and should be the default supplement form. Pair with vitamin K2 (MK-7) and take with a fat-containing meal for optimal absorption.
▲ Choose Vitamin if:
Strict vegans who object to animal-derived supplements. Note: lichen-derived D3 supplements are now widely available, providing a vegan source of D3 with superior efficacy to D2.
Can You Take Both?
No benefit to combining D2 and D3. If taking D2 for any reason, simply switching to D3 at a comparable or lower dose will provide better results.
Frequently Asked Questions
The Bottom Line
Vitamin D3 (cholecalciferol) is the clear winner for supplementation. Multiple RCTs and meta-analyses confirm D3 raises serum 25(OH)D levels 87% more effectively than D2 at equivalent doses and sustains those levels for longer. D3 is the form naturally produced in human skin from sunlight.