Difference Between Vitamin D & Vitamin D-3

By Jill Corleone, RDN, LD

Vitamin D is found in only a few foods, and both men and women in the United States have a difficult time meeting their daily needs without supplementation, according to the Office of Dietary Supplements. As a supplement, vitamin D is available in two forms: vitamin D-2 and vitamin D-3. Vitamin D-2, however, may not be as effective as D-3. Consult your doctor if concerned about your vitamin D intake and need for supplementation.

Male doctor talking to a male patient

Vitamin D is found in only a few foods, and both men and women in the United States have a difficult time meeting their daily needs without supplementation, according to the Office of Dietary Supplements. As a supplement, vitamin D is available in two forms: vitamin D-2 and vitamin D-3. Vitamin D-2, however, may not be as effective as D-3. Consult your doctor if concerned about your vitamin D intake and need for supplementation.

About Vitamin D

The fat-soluble vitamin performs a number of different functions in the body. In addition to helping you absorb calcium, vitamin D helps keep bones healthy and strong by assisting in their growth and maintenance. Vitamin D also helps you fight off infection by supporting immune health, and it helps reduce inflammation.

Even though your body can make its own vitamin D through sun exposure, the Institute of Medicine has established recommended dietary allowances, which for adults range from 600 to 800 international units a day.

Active Vitamin D

Whether from food, the sun or supplements, the vitamin D is initially in an inactive form and must undergo a two-step process to become active and usable by the body. First, the vitamin D is converted to calcidiol in the liver, chemically referred to as 25-hydroxyvitamin D. Then the calcidiol is converted to calcitriol, or 1,25-dihydroxyvitamin D, in the kidneys, the metabolically active form of vitamin D.

Plant-Made Vitamin D-2

Vitamin D-2, also referred to as ergocalciferol, is a form of vitamin D made by plants through photosynthesis when exposed to ultraviolet light. This is the type of vitamin D you get from UV-exposed mushrooms. It's also sometimes used to fortify foods such as milk.

The Office of Dietary Supplements reports that vitamin D-2 is an acceptable supplement because it helps prevent rickets. When given at high doses, vitamin D-2 may not be as effective as vitamin D-3.

Vitamin D-3

Vitamin D-3, also known cholecalciferol, is the form of vitamin D your body makes when exposed to the sun. Most of the vitamin D found in animal foods, including egg yolks, cheese and liver, is in the form of vitamin D-3.

As a supplement, vitamin D-3 is made by irradiating fat from sheep's wool. Most prescription forms of vitamin D are in the form of vitamin D-3.

References

About the Author

Jill Corleone is a registered dietitian and health coach who has been writing and lecturing on diet and health for more than 15 years. Her work has been featured on the Huffington Post, Diabetes Self-Management and in the book "Noninvasive Mechanical Ventilation," edited by John R. Bach, M.D. Corleone holds a Bachelor of Science in nutrition.

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