Page 184

and Their Children 1-5 Years, 4 Days, 1985. Report No. 85-4. Nutrition Monitoring Division, Human Nutrition Information Service, Hyattsville, Md. 182 pp.

Wargovich, M.J., V.W.S. Eng, H.L. Newmark, and W.R. Bruce. 1983. Calcium ameliorates the toxic effect of deoxycholic acid on colonic epithelium. Carcinogenesis 4: 1205-1207.

PHOSPHORUS

Phosphorus is an essential component of bone mineral, where it occurs in the mass ratio of 1 phosphorus to 2 calcium. Approximately 85% (700 g) of the phosphorus in the adult body is found in bone. Phosphorus also plays an important role in many and varied chemical reactions in the body. It is present in soft tissues as soluble phosphate ion; in lipids, proteins, carbohydrates, and nucleic acid in an ester or anhydride linkage; and in enzymes as a modulator of their activities. Energy for metabolic processes derives largely from the phosphate bonds of adenosine triphosphate (ATP), creatine phosphate, and similar compounds.

Phosphorus is efficiently absorbed by the small intestine as free phosphate (Avioli, 1988). Phosphorus absorption probably takes place by three different mechanisms: (1) calcium-coupled, vitamin D-dependent; (2) noncalcium-coupled, vitamin D-dependent; and (3) noncalcium coupled, vitamin D-independent (Parfitt and Kleerekoper, 1980).

Infants absorb from 65 to 70% of the phosphorus in cow's milk and 85 to 90% of that in human milk. Children and adults absorb 50 to 70% of the phosphorus in normal diets and as much as 90% when the intake is low (LSRO, 1981).

Polyphosphate (sodium hexametaphosphate), which is used in the processing of food, is efficiently hydrolyzed to orthophosphate in the intestine, where it is well absorbed (Zemel and Linkswiler, 1981). Approximately 50% of phytate phosphorus is absorbed (Parfitt et al., 1964).

Dietary Sources and Usual Intakes

Phosphorus is present in nearly all foods. The amount available in the food supply from unprocessed primary commodities, about 1,430 to 1,520 mg per capita per day, has been relatively constant during the past 75 years, despite marked changes in food consumption patterns (Bunch, 1987). The mean daily phosphorus intake is approximately 1,500 mg/day for adult males (USDA, 1986) and 1,000 mg/ day for adult females (USDA, 1987). True intakes may be 15 to 20%