Synthesis

• Vitamin D2, ergocalciferol, is synthesized when plants, fungi and some invertebrates are exposed to UVB rays from the sun. One of the few good food sources of Vitamin D2 is button mushrooms; however these mushrooms must be irradiated for the Vitamin D2 levels to be significant. Vitamin D3, cholecalciferol, is synthesized in the skin of vertebrates during exposure to UVB rays and can be found in fish, eggs, meat, dairy and poultry.
  
  

Function

• Both Vitamin D2 and Vitamin D3 are absorbed by the intestines and converted into active forms of Vitamin D in the body by the liver and kidneys. After this process is complete, active Vitamin D helps to maintain calcium and phosphorus balance in the body.
  
  

Research

• In a study published by Dr. Michael Holick and colleagues in the Journal of Clinical Endocrinology & Metabolism in 2007, research showed that there was no difference in active Vitamin D levels when comparing people who ingested either Vitamin D2 or Vitamin D3.