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Calcidiol and Calcitriol

author image Jamie Yacoub
Jamie Yacoub is a clinical outpatient Registered Dietitian, expert in nutrition and author of her cookbook "Modern Guide to Food and Eating: Low Glycemic Recipes". She obtained a Bachelor of Science in clinical nutrition from UC Davis and an MPH in nutrition from Loma Linda University. Yacoub then completed her dietetic internship as an intern for a Certified Specialist in sports nutrition and at a top-100 hospital.
Calcidiol and Calcitriol
Help prevent both vitamin D and calcium deficiency by getting at least 15 minutes of sun per day. Photo Credit: m-imagephotography/iStock/Getty Images

Vitamin D is both a vitamin and a hormone that your body makes. Calcidiol and calcitriol are two different forms of vitamin D in your body. Calcidiol is a precursor of calcitriol, which is the active form of vitamin D in your body and helps carry out the major functions of vitamin D. You can obtain vitamin D from sunlight and a few food sources, including swordfish, salmon, egg yolk and fortified foods such as milk, orange juice and breakfast cereals.

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How Many Ds Does It Take

Your body absorbs an ingredient needed to synthesize vitamin D, called 7-dehydrocholesterol, from sunlight on your skin and from food sources. Your liver then converts 7-dehydrocholesterol to calcidiol. Calcidiol is 25-hydroxy vitamin D. According to the National Institutes of Health, the most accurate way for your doctor to test your vitamin D status is to test the 25-hydroxy vitamin D level in your blood. The normal laboratory value range for 25-hydroxy vitamin D is 30 to 74 nanograms per milliliter of blood. Calcidiol is not an active form of vitamin D until it is converted to calcitriol.

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Calcitriol, 1,25-dihydroxyvitamin D, is converted in the kidneys from calcidiol. Calcitriol then carries out the major functions of vitamin D in your body, including facilitating the absorption of calcium in your body, immune system function and muscle movement and nerve communication. According to the Harvard School of Public Health, the beneficial role of vitamin D likely is not only limited to these body functions. Harvard states that promising research links adequate vitamin D intake with increased bone and muscle strength and reduction in the risk of heart disease, cancer, type one diabetes, the common cold, tuberculosis and premature death.

When Vitamin D Goes Up, Calcium Follows

Calcidiol and calcitriol are available in supplement form by prescription only. These medications are most commonly given to people whose kidneys or parathyroid glands are not functioning properly and are used to to treat low levels of calcium in the body, which can lead to bone weakening and osteoporosis. You can buy over-the-counter vitamin D supplements in the form of vitamin D-2, called ergocalciferol, and vitamin D-3, or cholecalciferol. These two supplements are also used to treat patients whose kidneys or parathyroid glands are not functioning properly. More research is needed on which of these four supplements works better and if their effectiveness differs per situation.

15 Minutes a Day Keeps the Doctor Away

If you are vitamin D deficient, your doctor will not likely prescribe calcitriol or calcidiol; instead, he will probably give you vitamin D-3 or vitamin D-2. To prevent vitamin D deficiency, get enough sunlight and eat food sources of vitamin D. The Harvard School of Public Health recommends taking a 15-minute daily walk in the sun. Your absorption of vitamin D depends on multiple factors, including your skin tone, weight and age. Among the best food sources of vitamin D are swordfish and salmon; 3 ounces of cooked swordfish contains 142 percent of your Daily Value for vitamin D, while 3 ounces cooked sockeye salmon contains 112 percent DV. One large egg has 10 percent DV in the yolk; 1 cup fortified orange juice provides 34 percent DV; and 1 cup fortified milk contains 29 to 31 percent DV.

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