Role of Vitamin D

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Role of Vitamin D

The major role of vitamin D is to maintain normal blood levels of calcium and phosphorus. Vitamin D helps the body absorb calcium, which forms and maintains strong bones. It is used alone or together with calcium to improve bone health and decrease fractures. Vitamin D may also protect against osteoporosis, high blood pressure, cancer, and other diseases. Table 1 identifies the various forms of Vitamin D and their associated functions within the human body.
Table 1. Forms of Vitamin D and their Function.
Forms of Vitamin DFunction within the Body
D2 (Ergocalciferol)
  • Absorption of calcium and phosphorus
D3 (Cholecalciferol)
  • Helps the body absorb calcium
Calcidiol (25-hydroxyvitamin D)
  • Not an active form of vitamin D until converted to calcitriol (1,25-dihydroxyvitamin D)
  • Converted in the kidneys
Calcitriol (1,25-dihydroxyvitamin D)
  • Increases the level of calcium (Ca2+) in the blood by increasing the uptake of calcium from the gastrointestinal tract
  • Increases reabsorption of calcium by the kidneys
  • Increases release of calcium from the bone