Vitamin D3, also called cholecalciferol, is the form of vitamin D the body naturally makes from sunlight. Vitamin D2, also called ergocalciferol, is sometimes used in supplements. Most experts recommend taking vitamin D3 rather than D2; these are the two forms of vitamin D, according to Everyday Health.
The body makes vitamin D3 when the skin is exposed to sunlight. Vitamin D3 supplements are made using the fat from lambs' wool, explains WebMD. In contrast, Vitamin D2 supplements are made by applying radiation to fungus. Natural vitamin D is found in some foods, including oily fish and egg yolks. Other foods, including milk and some breakfast cereals, are fortified with vitamin D.
Some nutritionists, including WebMD nutritionist Kathleen Zelman, recommend taking vitamin D3 rather than vitamin D2 because it is the form that is naturally made by the body. Vitamin D3 may also be easier to absorb, notes Everyday Health. The final benefit of vitamin D3, compared to vitamin D2, is the body limits the amount of D3 that can circulate in the blood, so the risk of taking too much is lower.
Vitamin D3 can interact with some medications, states Everyday Health. People who take bile acid sequestrants or the weight-loss drugs Alli or Xenical should speak to a doctor before taking vitamin D3 supplements.