Bone mineral consists of calcium phosphate. Adequate dietary phosphorus is therefore as important as calcium for building bone. Without it, the patient will develop a form of osteomalacia; they will not mineralize the skeleton. Fortunately, phosphorus is plentiful in many plant and animal tissues and if one has a diet with adequate protein, it also likely contains adequate phosphorus. Dairy products, meat, and fish are good sources of phosphorus.
Absorption of phosphorus is highly efficient. Net absorption is about 55-80%. Phosphorus is also efficiently retained by the body by reducing urinary phosphorus excretion. However, calcium supplements may interfere with phosphorus by acting as a binder and reducing its absorption from the GI tract. This is a good example of the general rule that food sources of nutrients are superior to a nutrient ingested in isolation. In this case, a serving of dairy food will supply phosphorus in addition to the calcium and protein needed for bone health.
The RDA for phosphorus for adults is 700 mg/day and most of the US population obtains enough of the mineral from their diet. However, some groups may have an inadequate intake such as people eating a weight-reduction diet. Another problem group is older women who eat poorly: 10% of women >60 years and 15% of women >80 years consume <70% of the RDA for phosphorus. This group is also likely to have a diet deficient in other nutrients, including calcium and protein. Also of concern are those eating very strict vegetarian diets as these do not contain enough phosphorus in a usable form.