the second most abundant element (after calcium) present in our bodies, makes up about 1 percent of our total body weight. It is present in every cell, but 85 percent of the phosphorus is found in the bones and teeth. In the bones, phosphorus is present in the phosphate form as the bone salt calcium phosphate in an amount about half that of the total calcium. Both these important minerals are in constant turnover, even in the bone structure.
The body uses a variety of mechanisms to control the calcium-phosphorus ratio and metabolism. The ratio of these two elements in the diet has been the subject of much recent interest. The typical American diet provides too much phosphorus and not enough calcium, leading to reduced body storage of calcium; thus, many of the problems of calcium deficiency discussed earlier may develop. Phosphorus and calcium can compete for absorption in the intestines. High consumption of meats or soft drinks increases phosphorus intake and may contribute to this imbalance. The ideal ratio of calcium to phosphorus in the diet is 1:1.
Phosphorus is absorbed more efficiently than calcium. Nearly 70 percent of phosphorus is absorbed from the intestines, although the rate depends somewhat on the levels of calcium and vitamin D and the activity of parathyroid hormone (PTH), which regulates the metabolism of phosphorus and calcium. Most phosphorus is deposited in the bones, a little goes to the teeth, and the rest is contained in the cells and other tissues. Much is found in the red blood cells. The plasma phosphorus measures about 3.5 mg. (3.5 mg. of phosphorus per 100 ml. of plasma), while the total blood phosphorus is 30-40 mg.. The body level of this mineral is regulated by the kidneys, which are also influenced by PTH. Phosphorus absorption may be decreased by antacids, iron, aluminum, or magnesium, which may all form insoluble phosphates and be eliminated in the feces. Caffeine causes increased phosphorus excretion by the kidneys.
Sources: Since phosphorus is part of all cells, it is readily found in food, especially animal tissues. Most protein foods are high in phosphorus. Meats, fish, chicken, turkey, milk, cheese, and eggs all contain substantial amounts. Most red meats and poultry have much more phosphorus than calcium-between 10 and 20 times as much-whereas fish generally has about 2 or 3 times as much phosphorus as calcium. The dairy foods have a more balanced calcium-phosphorus ratio. Seeds and nuts also contain good levels of phosphorus (although they have less calcium) as do the whole grains, brewer's yeast, and wheat germ and bran. Most fruits and vegetables contain some phosphorus and help to balance the ratio of phosphorus to calcium in a wholesome diet.
In recent years, the increased consumption of soft drinks, which are buffered with phosphates, has been a concern. There may be up to 500 mg. of phosphorus per serving of a soft drink, with essentially no calcium. In 1970, the average per capita intake of soft drinks was 23 gallons, whereas in 1981, 39 gallons a year were consumed by the "average" person. Since some people do not drink any of these "beverages," quite a number of people are drinking even more than the average amount of soda pops, and thus consuming a lot of phosphorus.
Functions: Phosphorus is involved in many functions besides forming bones and teeth. Like calcium, it is found in all cells and is involved in some way in most biochemical reactions. Phosphorus is vital to energy production and exchange in a variety of ways. It provides the phosphate in adenosine triphosphate (ATP), which is the high-energy carrier molecule in the body's primary metabolic cycles. Phosphorus is important to the utilization of carbohydrates and fats for energy production and also in protein synthesis for the growth, maintenance, and repair of all tissues and cells. As inorganic phosphate in ATP, it is needed in protein synthesis and in the production of the nucleic acids in DNA and RNA, which carry the genetic code for all cells.