Ergocalciferol (Vitamin D2)

Functional but inferior to vitamin D3 for supplementation. Primarily relevant for vegans who avoid D3 (typically lanolin-derived).

A rough internal score reflecting quantity, quality, and consistency of human evidence. Not a clinical recommendation.

Head-to-head trials consistently show D3 is 2–3x more effective at raising serum 25(OH)D. D2 has a shorter half-life and lower binding affinity to vitamin D-binding protein. Still used in prescription megadoses (50,000 IU).

• Plant-derived vitamin D suitable for vegans
• Raises serum 25(OH)D levels (less efficiently than D3)
• Available in high-dose prescription forms

Higher doses needed compared to D3 to achieve equivalent serum levels. Typically 1000–4000 IU daily, or 50,000 IU weekly for deficiency correction.

• Hypercalcemia at chronic high doses
• GI discomfort
• Same toxicity profile as D3

Same toxicity potential as D3 at high doses (hypercalcemia). Less efficient dosing means higher risk of under-supplementation.

D3 is preferred unless there are specific reasons to use D2 (vegan preference, prescription availability). Lichen-derived D3 is now available as a vegan alternative.

• Immunity60
• Longevity55
• Mood35