Vitamin D2 (Ergocalciferol)

Produced by UV-irradiation of fungus (mushrooms) or yeast
Only vegan source of Vitamin D supplementation & commonly used to fortify food especially in the US
Vitamin D2 supplements may not be as effective as Vitamin D3 supplements at the same doses
Evidence suggests there is no difference in the efficiency of Vitamin D2 and Vitamin D3 in treating Ricketts


Vitamin D3 (Cholecalciferol)

Naturally produced in the skin by solar UV irradiation (sunlight)  
Also can be produced from sheep lanolin by UV-irradiation (for supplement production)
Recently , used more for supplementation in Europe

(6,7,8,9,10)