Phosphorus is an important mineral of the body. The adult human being has about 700 grams of phosphorus which makes about 1% of the body weight. About 85% of it is in the skeleton. The whole blood contains about 48 mg phosphorus/dL which is chiefly present in the form of inorganic phosphorus, organic phosphate esters, and lipid phosphorus. The red blood cells contain more phosphorus than plasma and contain much more organic phosphate form.
Foods rich in calcium are also generally rich in phosphorus and these include milk which contains about 93% of phosphorus, beans, cereals, egg yolk, and meats. A large part of the vegetable phosphorus exists as phytates of calcium and magnesium which are insoluble and are largely not absorbed. A disadvantage of the phytates is that they interfere with the absorption of calcium, zinc, and iron. Phosphorus is also present in the phosphate food additives.
Absorption and Excretion
The phosphorus ingested with foods is absorbed in the form of inorganic phosphate by an active energy-dependent process and about 2.3% of ingested phosphate is absorbed. The active form of vitamin D greatly stimulates the absorption of phosphorus. Its re-absorption is blocked by parathyroid hormone and therefore increased urinary loss of phosphorus. All forms of phosphorus are excreted via urine, and the phosphorus present in the feces are represented by the unabsorbed form.
- Phosphorus takes part in the formation of bones and teeth; about 85% of body phosphorus is in the bones. The scleroprotein and collagen also contain phosphorus.
- Phosphorus forms a part of the high energy phosphate compound such as ATP, GTP, CTP, UTP, TTP and creatine phosphate.
- It is a constituent of nucleic acid both DNA and RNA, which are of great importance from the standpoint of protein synthesis, viruses, cancer, and genetics.
- It is a constituent of phospholipids such as lecithin, cephalin, plasminogens etc.
- Phosphorus is an important constituent of cell membranes.
- Phosphates are the most abundant anions present within tissues cells.
- The plasma phosphate takes part in buffer action concerned with hydrogen excretion in urine for plasma pH regulation.
- They form esters with sugars, for example, glucose 6 phosphate, fructose 6 phosphate etc which takes part in carbohydrates metabolism.
Deficiency of phosphorus rarely occurs since it is widely available in the foods we eat. In case if deficiency occurs it may lead to hypophosphatemia which is associated with myophaty, cardiomyopathy, and symptoms due to osteomalacia which is bone pain and waddling gait. Children may show retard growth. A decreased level of 2,3BPG and ATP in red blood cells (RBCs) may result in tissue hypoxia.
If high phosphorus levels are maintained for longer periods, then calcium phosphate may be deposited in abnormal sites and leads to a condition called hyperphosphatemia.
It has been suggested that phosphorus intake should be equal to calcium intake in most of the age groups except in infancy where the ratio considered good is 1:1.5.