What are its key functions?


Adapted from DeLuca, HF 1

Plasma calcium concentrations are maintained at a very constant level, and this level is supersaturating with respect to bone mineral. If the plasma becomes less than saturated with respect to calcium and phosphate, then mineralisation fails, which results in rickets among children and osteomalacia among adults.
The vitamin D hormone functions to increase serum calcium concentrations through 3 separate activities. 

  1. It is the only hormone known to induce the proteins involved in active intestinal calcium absorption. Furthermore, it stimulates active intestinal absorption of phosphate. 
  2. Blood calcium concentrations remain in the normal range even in the absence of calcium in the diet. 
  3. The distal renal tubule is responsible for reabsorption of the last 1% of the filtered load of calcium.


  1. De Luca, H.F. Am J Clin Nutr 2004; 80(suppl):16896-96s