Phosphorus

Description

Phosphorus comprises approximately from 0.8% to 1.1% of total body weight. 80-90% of this phosphorus is found within the skeleton and teeth, where it is compounded with calcium to form calcium phosphate. Calcium phosphate is a primary constituent of hydroxyapatite crystals in bone and teeth, and helps to add structural rigidity to the softer organic portions.

Phosphorus plays an important role in almost all cell metabolic activities. It is a major constituent of the molecule phosphate, which is instrumental in the storage of energy as adenosine triphosphate (ATP) molecules.

Phosphorus is an essential component of RNA and DNA, and is a part of the molecular structure of phospholipids, the key components in the structure of cell membranes. The phosphate group is of primary importance in glycolysis. It is also present in many enzymes and proteins.

Phosphate is instrumental in maintaining the acid/base balance in the body by acting as a buffer.

It also activates many of the vitamin B-Complex vitamins, allowing them to function as coenzymes in various metabolic processes.

Method of Action

Phosphorus is most abundantly seen in the body as a constituent of calcium phosphate, one of the bone salts which add structural rigidity to the softer protein matrix of bone and teeth.

Perhaps phosphorus' most important metabolic role is as a constituent of the molecule phosphate. When this molecule links to an adenosine pyrophosphoric acid (ADP) molecule adenosine triphosphate (ATP) is formed, possessing a a high energy phosphate bond. When broken, this bond releases its energy and the phosphate, reforming an ADP molecule.

The ATP "energy" molecule is formed during glycolysis and other processes involving the release of chemical energy from food. ATP is used as the primary source of energy for many metabolic and enzymatic activities, especially muscle contraction, active transport, and the formation of DNA. Phosphate is an important constituent of RNA and DNA. It serves to link the individual bases with one another.

The energy released from the high energy phosphate bond of ATP is essential for the operation of the sodium/potassium pump, which exchanges three sodium ions for two potassium ions across a biological membrane. This pump is used to regulate relative amounts of sodium and potassium excreted and retained in the body.

Phosphate, from ATP, reacts with choline to initiate the synthesis of phospholipids which are essential constituents of cell membranes. Phospholipids are instrumental in regulating cellular permeability and are found in the exterior membrane of nerve cells. They are also helpful in solubilizing relatively nonsoluble triglycerides and cholesterols.

ADP, which contains two phosphate molecules, is a constituent of blood platelets and is secreted from platelet granules to stimulate platelet aggregation for blood clotting.

Phosphate also plays an important role, due to its effective buffering action, in maintaining acid/base balance in blood plasma.

Phosphorus absorption is about 50-70% efficient, as calcium, iron, and zinc tend to complex with phosphorus in the stomach, thus reducing absorption. Vitamin D tends to promote the absorption of both phosphorus and calcium from the intestine. Excretion through the urine regulated the body's level of phosphorus.

Properties & Uses

Phosphorus supplementation is important in patients with low phosphate to calcium ratios for promotion of proper bone and tooth mineralization, especially in younger persons.

Phosphorus may also be beneficial in reversing, to some extent, osteomalacia, rickets, bone pain, and muscle weakness experienced by persons with hypophosphatemia.

Consequence of Deficiency

Phosphorus deficiency is extremely rare and occurs primarily in persons who use phosphate-binding antacids or who suffer abnormally excessive urinary losses. The principal symptoms include fatigue, anorexia, and demineralization of bone. Other possible symptoms include osteomalacia, convulsions, and abnormal or incomplete mineralization of developing teeth.

Phosphate deficiencies can be the result of defective renal phosphate absorption, as seen in familial vitamin D-resistant rickets, a genetically linked disorder which affects vitamin D utilization. Symptoms are characteristic of other forms of rickets.

Toxicity Factors

Phosphorus is not toxic in large amounts, although a disproportionately large amount of phosphorus relative to calcium can induce an increased fecal excretion of calcium, possibly resulting in a calcium deficiency.

In patients with renal insufficiencies, there may be a decreased urinary excretion of phosphorus, resulting in high blood phosphate levels. This condition may result in skeletal demineralization and mineral resorption. This condition can be controlled by ingestion of aluminum hydroxide or calcium carbonate, both of which reduce phosphate absorption.

Recommended Dietary Allowance

age	RDA (mg)
infants/children
0-6 months	300
6-12 months	500
1-10 years	800
males
11-24 years	1200
25+ years	800
females
11-24 years	1200
25+ years	800
pregnancy	1200
lactation	1200

Food Sources

Artichokes	Bean (dried)
Beef	Beef liver
Broccoli	Cheese
Chicken	Chicken liver
Egg	Green pea
Ice cream	Lamb liver
Lentil	Lima bean
Milk	Mushroom
Orange sherbet	Parsnip
Peanut	Pork
Potato	Sardines
Turkey liver	Veal liver
White bread (enriched)	Whole wheat bread
Winter squash	Yogurt

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