12.3 Phosphorus

Phosphorus

Animal products are rich sources of phosphate. Plant products contain phosphorus, but some is in the form of phytic acid (phytate). In grains, over 80% of the phosphorus is phytate. The bioavailability of phosphorus from phytate is poor (~50%) because we lack the enzyme phytase2. Nevertheless, ~50-70% of phosphorus is estimated to be absorbed from our diet1.

Another source of phosphorus is phosphoric acid that is used to acidify colas. Colas are caramel-colored, carbonated soft drinks that contain caffeine, such as Coca-Cola, Pepsi, etc.

Epidemiological studies have found that soft drink consumption is associated with decreased bone mineral densities, particularly in females3,4. It has been hypothesized that phosphoric acid

plays some role in this effect, but there is limited evidence to support this belief. Most phosphorus is excreted in the urine.

Phosphorus deficiency is rare, but can hinder bone and teeth development. Other symptoms include muscle weakness, rickets, and bone pain5. Toxicity is also rare, but it causes low blood calcium concentrations and tetany1.

http://lpi.oregonstate.edu/mic/minerals/phosphorus#reference10

Subsection:

• 12.31 Phosphorus Functions

References & Links

• Gropper SS, Smith JL, Groff JL. (2008) Advanced nutrition and human metabolism. Belmont, CA: Wadsworth Publishing.
• Phosphorus. Linus Pauling Institute Micronutrient Information Center. http://lpi.oregonstate.edu/mic/minerals/phosphorus#reference10
• Tucker K, Morita K, Qiao N, Hannan M, Cupples LA, et al. (2006) Colas, but not other carbonated beverages, are associated with low bone mineral density in older women: The framingham osteoporosis study. Am J Clin Nutr 84(4): 936-942.
• Libuda L, Alexy U, Remer T, Stehle P, Schoenau E, et al. (2008) Association between long-term consumption of soft drinks and variables of bone modeling and remodeling in a sample of healthy german children and adolescents. Am J Clin Nutr 88(6): 1670-1677.
• Byrd-Bredbenner C, Moe G, Beshgetoor D, Berning J. (2009) Wardlaw’s perspectives in nutrition. New York, NY: McGraw-Hill.

12.31 Phosphorus Functions

Phosphorus has a number of functions in the body1.Phosphate is a component of hydroxyapatite in bones and teeth, and can have non-bone function.

Non-bone functions include:

Phosphorylation – Phosphates are used to activate and deactivate a number of proteins. In addition, compounds are also frequently phosphorylated, like the monosaccharides shown below.

Figure 12.311 Uptake of monosaccharides into the hepatocyte Phospholipids – Phosphates are a component of phospholipids DNA/RNA – DNA/RNA have a phosphate backbone as shown below.

Figure 12.313 Structure of DNA2

ATP – The major energy currency, ATP, stores energy in its phosphate bonds.

Secondary Messengers – The intracellular secondary messengers cyclic AMP (cAMP) and inositol triphosphate (IP3) both contain phosphate. The action of these secondary messengers can be seen in the links below.

Required Web LinkscAMP IP3

References & Links

• Gropper SS, Smith JL, Groff JL. (2008) Advanced nutrition and human metabolism. Belmont, CA: Wadsworth Publishing.
• http://en.wikipedia.org/wiki/File:DNA_chemical_structure.svg

Links

cAMP – http://courses.washington.edu/conj/gprotein/cyclicamp.htm IP₃ – http://courses.washington.edu/conj/gprotein/ip3.htm