Like calcium, phosphorus is stored in the body primarily in the bone, although nearly 100 g are present in the extracellular fluid, approximately 10 times the amount of extraskeletal calcium.
In the body, phosphorus is found mainly in the form of phosphate ions, which play a key role in energy generation. The phosphorylation of adenosine is the primary energy exchange system in the cell. Phosphorous molecules, in the form of phospholipids, are plentiful in cell membranes as well. The average daily intake of phosphorus is approximately 800 to 1,000 mg in the typical American diet, 60% of which is absorbed in the intestine. This rate of absorption can be increased to 90% via the action of vitamin D, if necessary; urinary excretion also helps maintain phosphorus balance. Bone remodeling can also modulate the serum concentration of phosphorus.