Phosphorous (P) is an essential mineral that plays pivotal roles in the structure and function of nearly every part of the body. Approximately 85% of phosphorus is located in the bones, with the rest making up the structure of the teeth, the cellular membranes, nucleic acids, and nucleotides. While not as famous as Calcium, Zinc or Iron, Phosphorus has been referred to by some scientists as the element, “around which life is built”. Deficiency can result in anorexia, impaired growth, osteomalacia, bone demineralization, muscle atrophy, weakness, cardiac irregularities, respiratory dysfunction and many other disorders. Some studies have been conducted to suggest that supplemental Phosphorus may benefit endurance exercise, and increase the ability to take up oxygen.
Dietary phosphorus absorption is about 60-70%; any excess absorbed is readily excreted in the urine. Since renal conservation of phosphorus occurs quite efficiently on low phosphorus diets, a deficiency rarely occurs in a healthy population. However, various disease states or conditions (e.g., gastrointestinal malabsorption, diabetes mellitus, renal tubular dysfunction, antacid abuse, and premature birth) can be associated with low blood phosphorus levels (i.e., hypophosphatemia) and depleted phosphorus stores.
New recommendations for dietary phosphorus include a value, the Recommended Dietary Allowance (RDA), which an individual should aim to meet, and a value, the Tolerable Upper Level (UL), which should not be exceeded. Intakes between the RDA and the UL ensure that serum phosphorus levels will be maintained in the normal range. Values for infants are called Adequate Intake (AI) levels, and are based on a significant portion of intake being from breast milk. It should also be noted that there are no additional requirements for P during pregnancy or lactation. The Recommended intake levels for P (mg per day) are set based on life stage groups. For infants 0 to 6, and 6 to 12 months, the RDA is 100 and 275 mg, respectively. No UL has been set for these ages as supplementation would be unlikely. For children 1 to 3 and 4 to 8 years, the RDA is 460 and 500, respectively, and the UL is 3000 mg. For youth 9 to 18 years, the RDA is 1250 mg, which indicates the higher need for phosphorus during the adolescent growth spurt; the UL for youth is 4000 mg. Adults 19 years and older have an RDA of 700 mg. The UL is 4000 mg up to age 70, then declines to 3000 mg after age 70 years.
Phosphorus is found widely distributed in foodstuffs. In the United States, the average daily intake is about 1600 mg for males and 1000 mg for females. In general, food sources rich in protein (milk, meat, eggs, legumes and grains) are also high in phosphorus. The relative contributions of food groups to phosphorus intake are: 60% from milk, meat, poultry, fish, and eggs; 20% from cereals and legumes; 10% from fruits and fruit juices; 4% from alcoholic beverages; and 3% from soft drinks and other beverages.
A diet containing a 2:1 dietary ratio of phosphorus to calcium can cause low blood calcium (hypocalcemia) and secondary hyperparathyroidism with excess bone resorption and bone loss in animals. Human breast milk, with a lower phosphorus content than cow milk, is considered better suited to the needs of the infant. For older ages, typical diets in the United States frequently exceed the recommended ratio; however, these diets are not believed to be harmful unless calcium intake is also very low. As intake of phosphorus rises, so does serum phosphorus. Elevated serum phosphorus levels (hyperphosphatemia) can occur in patients with renal failure due to a poor ability to excrete phosphorus in the urine. As indicated by UL values, intake of phosphorus exceeding 3 to 4 grams may be harmful in healthy individuals.