In combination with calcium as a compound called hydroxyapatite, phosphorus gives bone its strength. While most of the body’s phosphorus is tied up in bone, free phosphorus serves important functions in each and every cell of the body.
Phosphorus as phosphate combines with fats to form phospholipids which are the major constituent of the membranes surrounding cells. All energy storage in cells is in the form of phosphate bonds in creatine phosphate (muscle only) and ATP (all cells).
Phosphorus is also an important regulator. By a process called phosphorylation, phosphate molecules attach to sites on enzymes, cell-signaling molecules and hormones to activate them.
Phosphorus is contained in the molecules that make up DNA and RNA, is involved in the buffering of acidity within cells and as the compound 2,3-DPG it facilitates delivery of oxygen bound to hemoglobin to the cells.
Because the body gives top priority to all the important cellular functions of phosphorus, deficiency symptoms first show up in bone. Rickets, bone softening and deformity, is seen in children and osteomalacia is the adult equivalent. Muscle weakness is also common because of phosphorus’ role in energy generation. Excess phosphorus has the same bone softening effect because it blocks absorption of calcium and causes calcium release from bone.
The ideal calcium:phosphorus ratio is 1.2:1 for pregnant and growing animals but adults can tolerate up to 6:1 if total phosphorus intake is adequate. Grasses and grass hays may be borderline in phosphorus and/or not have the ideal Ca:P ratio. Grains, brans, beans and seeds are high in phosphorus when not being fed as part of a commercial balanced feed with calcium added.
Eleanor M Kellon, VMD