Vitamin D3 is the type of vitamin D that is made in your body when you are exposed to sunlight. If you do not get sufficient exposure to sunlight, or, if you are vitamin D deficient, your doctor may recommend that you take vitamin D3 supplements. There are different types of vitamin D3 made in your body. Only one of these forms, however, is commonly available as a vitamin D3 supplement.
Cholecalciferol
Cholecalciferol is the natural form of vitamin D3 that you make when you are exposed to sunlight. Most over-the-counter vitamin D supplements sold in stores are cholecalciferol. According to the Vegetarian Resource Group, most cholecalciferol supplements are made from the fat of lamb's wool and are not considered vegan. Cholecalciferol vitamin D3 can also be purified from cod liver oil.
Calcidiol
Calcidiol, or 25-hydroxyvitamin D3, is a prehormone that your body makes from cholecalciferol. The Vitamin D Council explains that this is the form of vitamin D3 that is measured in your blood when you get a traditional vitamin D test. When your doctor refers to levels of vitamin D in your blood, he is actually talking about calcidiol.
Calcitriol
Calcitriol is also known as 1,25-dihydroxyvitamin D3. This form of vitamin D3 is a potent steroid hormone that is made in your kidneys from calcidiol. According to Drugs.com, calcitriol is the active form of vitamin D3. A 2010 review article in the journal "Endocrinology & Metabolism Clinics of North America" highlights some of the data suggesting that calcitriol can act as an anticancer agent. This report explains that laboratory research shows that calcitriol can act to prevent cancer in animals, but may not be as effective at preventing some cancers in humans.
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