Vitamin D is the only vitamin whose biologically active form is a hormone. The term "vitamin D" refers to a family of related compounds. Vitamin D3 (also called cholecalcife-rol) is the form synthesized from cholesterol in sun-exposed skin. For healthy children and adults, exposing the hands, face, and arms on a clear summer day for 10-15 minutes several times each week provides adequate vitamin D. Vitamin D3 is the natural form of the vitamin found in animal products such as eggs, fish, and liver. Another form of vitamin D, vitamin D2 (ergocalciferol), is synthesized by certain fungi and is used in many supplements and as a food fortifier. However, vitamin D3 is the preferred form for humans as its bioavailability is twice that of vitamin D2.1
After absorption from foods or production in the skin, vitamin D is stored as 25-OH-vitamin D in the liver. When needed by the body, it is subsequently activated to 1,25 -OH-vitamin D by the kidney.1 Thus, a healthy liver and kidneys are essential for optimum vitamin D status. (1 jig vitamin D = 40 IU vitamin D.)
Was this article helpful?