Phosphorus

Question 1

Phosphorus distribution

Answer 1

• 85% in skeleton
• 14% in soft tissues
• 1% in blood and body fluids

Question 2

Phosphorus sources

Answer 2

• Meat, poultry, fish, eggs, and dairy
• Nuts, legumes and grains
• Coffee, tea, and soft drinks

Question 3

Phosphorus bioavailability

Answer 3

• Animal products are superior sources of available phosphorus
o Most of the phosphorus in meat is bound to organic compounds (proteins, lipids)
o Most of the phosphorus in plants is occurs as phytate (aka inositol hexaphosphate (IP6))

Question 4

Phosphorus digestion

Answer 4

• Phosphorus is absorbed in its inorganic form

* Organically bound phosphorus is hydrolyzed to inorganic phosphorus in the small intestine

Question 5

Phosphorus absorptio

Answer 5

• Absorption occurs throughout the small intestines, primarily in the duodenum and jejunum
• 2 processes
o Concentration-dependent facilitated diffusion is the primary rout of absorption
o Saturable, carrier-mediated transport system
• Dependent on sodium
• Enhanced by calcitriol and if phosphorus intake is low
• Factors influencing absorption
o Vitamin D – stimulates P absorption
o Phytate – inhibits P absorption
o Other minerals – magnesium, calcium, and aluminum compete with P for absorption

Question 6

Phosphorus transport

Answer 6

• Transported in inorganic and organic forms

o Most P transported as organic phosphate found in phospholipids and lipoproteins

Question 7

Phosphorus storage

Answer 7

• Stored in all cells but mostly in bone and muscle

Question 8

Phosphorus functions

Answer 8

• Structural Roles
o Bone mineralization
o As part of phospholipids and nucleic acids
• Energy production and storage: ATP, creatine phosphate
• Cell signaling & enzyme activity regulation: phosphorylation of various protein kinases by cAMP
• Acid-base balance: phosphate is a main intracellular buffer
• Oxygen availability
o 2,3-diphosphoglycerate (2,3-DPG) binds to hemoglobin in red blood cells and affects oxygen delivery to the tissues of the body

Question 9

Phosphorus excretion

Answer 9

• Excreted in its inorganic forms primarily in the urine

Question 10

Phosphorus deficiency

Answer 10

• Rare
o Patients with renal diseases
o Patients taking large amounts of antacids
• Ca, Mg, and aluminum bind phosphorus in the GI tract preventing its absorption

Question 11

Phosphorus preparations

Answer 11

• Hydroxyapatite - derived from refined bone powder

Question 12

Phosphorus toxicity

Answer 12

•	UL
o	9-70:  4 g
o	Pregnancy:  3.5 g
o	Lactation: 4 g
o	>70:  3 g
•	Extremely rare
•	Symptoms:  hypocalcemia → tetany

Question 13

Phosphorus assessment of status

Answer 13

• Rarely used as deficiency is so rare

* Serum and urinary concentrations both have low sensitivity and specificity