Vitamin D3 vs Vitamin D2 for efficacy and bioavailability
For most people seeking the strongest, most durable rise in vitamin D status, choose D3. D2 works, but on average raises and sustains 25(OH)D less, especially with bolus dosing. [1][2]
Across randomized trials and meta-analyses, D3 produces larger and more sustained increases in serum 25(OH)D than D2, particularly with intermittent/high-dose regimens, and has a slightly longer 25(OH)D half-life. D2 remains acceptable (and vegan) but may need higher or more frequent dosing and careful lab methods when monitoring. [1][2][3][4][8][7]
The Comparison
Standardization: Typically as cholecalciferol; potencies 400–10,000 IU/capsule
Dosage: 800–2,000 IU/day for maintenance; higher per clinician for repletion
Benefits
- •More effective at raising/maintaining serum 25(OH)D
- •Longer 25(OH)D half-life
- •Better performance with bolus dosing in RCTs
Drawbacks
- •Animal-derived in most products unless labeled vegan
Safety:Same UL and interactions as D2; see Safety section.
Standardization: As ergocalciferol; Rx 50,000 IU capsules exist
Dosage: 800–2,000 IU/day for maintenance; Rx 50,000 IU weekly used for short courses
Benefits
- •Plant/fungal-derived (vegan)
- •Effective at increasing total 25(OH)D, though typically less than D3
Drawbacks
- •Smaller, less durable rises in 25(OH)D on average
- •More assay variability with 25(OH)D2 measurements
Safety:Same UL and interactions as D3; see Safety section.
Head-to-Head Analysis
Ability to raise 25(OH)D (overall) Critical
Winner:Vitamin D3 (cholecalciferol)• Importance: high
Bolus/intermittent dosing performance Critical
Winner:Vitamin D3 (cholecalciferol)• Importance: high
Durability/half-life of 25(OH)D Critical
Winner:Vitamin D3 (cholecalciferol)• Importance: high
25(OH)D3 has a modestly longer plasma half-life than 25(OH)D2, aiding maintenance. [8]
Daily maintenance efficacy (physiologic doses)
Winner:Vitamin D3 (cholecalciferol)• Importance: medium
Long-term daily trials show greater or more sustained 25(OH)D with D3 vs D2. [4]
Effect on endogenous D3 metabolites
Winner:Vitamin D3 (cholecalciferol)• Importance: medium
D2 can lower circulating 25(OH)D3 and related metabolites; overall total 25(OH)D still rises but less than with D3. [3]
Assay reliability for monitoring
Winner:Vitamin D3 (cholecalciferol)• Importance: medium
Common immunoassays tend to underestimate 25(OH)D2; D3 monitoring is less affected (LC-MS/MS preferred for both). [7]
Special populations (e.g., CKD repletion)
Winner:Vitamin D3 (cholecalciferol)• Importance: medium
In CKD, D3 raised 25(OH)D more during therapy than D2 at equal doses. [5]
Dietary preference (vegan suitability)
Winner:Vitamin D2 (ergocalciferol)• Importance: low
D2 is plant-derived and widely vegan; note vegan D3 options also exist. [6]
Common Questions
Is D2 ever preferable to D3?
Yes—if you require a vegan option and cannot source vegan D3. D2 still raises total 25(OH)D, though often less than D3. [2]
Does D2 lower my body's D3?
D2 can reduce circulating 25(OH)D3, but total 25(OH)D still increases; a reciprocal effect is seen when taking D3. [3][9]
What dosing strategy is best for quick results?
Intermittent high-dose repletion favors D3 for larger, more sustained 25(OH)D rises. Follow clinician guidance. [1][3]
Do I need a blood test to choose a form?
Not usually; when monitored, ask for LC-MS/MS, especially if using D2 due to assay bias. [7][10]
What's the safe upper limit?
For adults, 4,000 IU/day unless supervised medically; check interactions if on certain meds. [6]
Which Should You Choose?
Rapid repletion or intermittent high-dose protocols
Choose:Vitamin D3 (cholecalciferol)
Everyday maintenance (800–2,000 IU/day)
Choose:Vitamin D3 (cholecalciferol)
Strict vegan preference with limited access to vegan D3
Choose:Vitamin D2 (ergocalciferol)
Situations where lab monitoring uses immunoassays
Choose:Vitamin D3 (cholecalciferol)
25(OH)D2 is more often underestimated; D3 reduces assay-related misclassification risk. Use LC-MS/MS when possible. [7]
Chronic kidney disease patients needing repletion (non-dialysis)
Choose:Vitamin D3 (cholecalciferol)
Equal-dose RCT favored D3 during active therapy. [5]
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