Key Concepts

  • RDA – 700 mg/day (adults)
  • UL – 4,000 mg/day
  • Deficiency is Rare – Men consume 1,602 mg/day & women 1,128 mg/day on average
  • Plants and seeds contain phytates which inhibit absorption of phosphorus
  • Food Sources: Salmon, dairy, liver, beef, chicken, eggs, tofu, legumes, nuts, seeds

Recommended Dietary Allowance (RDA)

The recommended dietary allowance (RDA) for adults is 700 mg/day. RDA varies in infants, children, adolescents, and pregnant or lactating women.

Functions

Phosphorus is the second most abundant mineral in the body. It is critical in the formation of bones and teeth and helps give them strength and rigidity. Phosphorus plays this role in the form of hydroxyapatite which is a calcium phosphate salt. Phosphorous is required for the formation of ATP and coenzymes such as NADP. Phosphorus is a key component in the structure of nucleotides and nucleic acids and plays an essential role in the biosynthesis of phospholipids in cell membranes as well as in the metabolism of carbohydrates. Normal pH is maintained in part by phosphorus which acts as a buffer. Additionally, 2,3-diphosphoglycerate (2,3-DPG), which contains phosphorus, regulates oxygen delivery to tissues by binding to hemoglobin in red blood cells.

Deficiency

Phosphorus deficiency is rare and can cause muscle weakness, bone pain, loss of appetite, anemia, rickets (in children), osteomalacia (in adults), increased susceptibility to infection, numbness and tingling of the extremities, difficulty walking, and respiratory failure. The body tightly regulates phosphorus levels in the blood so even inadequate intakes of phosphorus rarely result in low blood levels of phosphorus.

In the U.S., average daily intakes for men is around 1,602 mg; for women average in take is around 1,128 mg.

Toxicity/Excess/Upper Intake Level (UL)

The tolerable upper intake level for phosphorous is 4,000 mg/day. Excess phosphorus consumption can lead to the calcification of non-skeletal tissues, especially the kidneys, and increase the risk for both cardiovascular disease and bone fracture. Those with impaired kidney function or other disorders known to limit excretion of excess phosphorus are advised by the Institute of Medicine (IOM) to monitor their phosphorus intake more closely with the help of a physician.

Regulation

  • Absorbed in small intestine
  • Excess excreted by kidneys under regulatory action of PTH, vitamin D, & FGF-23
  • Blood calcium drops – parathyroid glands secrete more PTH – decreases urinary excretion of calcium, increases urinary excretion of phosphorus, stimulates bone resorption; calcium and phosphate released from bone – serum calcium concentrations reach normal levels; PTH also stimulates vit D to be converted to active form (calcitriol) in kidneys. Calcitriol increases intestinal absorption of Ca & P
  • Increased P intake: FGF-23 secreted by osteoblasts/osteocytes – (Negative feedback loop: FGF-23 inhibits production and stimulates degradation of calcitriol & promotes urinary excretion of P)

Food Sources

  • Salmon (chinook, cooked) – 3 oz – 315 mg
  • Yogurt (plain, nonfat) – 8 oz – 306 mg
  • Turkey (light meat, cooked) – 3 oz – 217 mg
  • Chicken (light meat, cooked) – 3 oz – 135-196 mg
  • Lentils (cooked) – ½ cup – 178 mg
  • Almonds (1 oz, 23 nuts) – 136 mg
  • Egg (hard-boiled) – 1 large – 86 mg

Food additives are also a dietary source of phosphorus as well as sodas (in the form of phosphoric acid).

Bioavailability

Plants and seeds contain phytates which inhibit the absorption of phosphorus by 50%. Soaking, sprouting, fermenting, and cooking reduce phytates, but the bioavailability of phosphorus is still not equal to that of animal sources even when these methods are utilized.

 

 

References/Resources

  1. http://lpi.oregonstate.edu/mic/minerals/phosphorus – food-sources

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