Food Sources
What types of foods is phosphorus naturally found in?
Animal products/Dairy: eggs, milk, cheese, etc.
Whole Grains
Pulses & Legumes
Nuts
Soy
What compounds inhibits and/or enhances phosphorus absorption?
Inhibits:
Phytic acid
Excessive nutrients: Mg, Al, Ca (e.g., antacids)
Enhances:
Calcitriol (1,25-dihydroxyvitamin D)
What is the role of phosphorus in the bones?
What is the RDA of phosphorus?
700mg
What hormone do osteoblasts secrete and how does this affect phosphorus?
FGF-23, secreted when phosphorus is high and promotes urinary excretion and impaired bone mineralization
Name the forms phosphorus from highest bioavailability to lowest.
Phosphate Additives; high
Phosphate; ~80%
Phosphorus: Elemental
Phytate; ~30–50%
Explain why is phytate less bioavailable for humans.
Phosphorus is bound to phytic acid in plant foods and requires the phytase enzyme to be release for absorption. Humans lack the phytase enzyme, resulting in reduces absorption.
Name 3 regulatory roles of phosphorus in the body.
-High-energy storage (ATP)
-Intracellular signalling
-Oxygen availability
-Phosphorylation (DNA, cAMP)
What is the UL of phosphorus in pregnant women?
3.5g
What measure of status ranges from 2.5-4.5mg/dL?
Plasma Pi Concentration
What is the most used phosphorus additive?
Inorganic phosphate salts (i.e. Na3PO4)
- sodium-phosphate, calcium phosphate, etc.
Other:
- Phosphoric acid: Colas (25-40mg/can)
Processed food
Anti-caking agents
CaHPO4: fortification
E.g.: Instant puddings, baking powder
Explain the process of phosphate absorption including location and mechanisms.
What is more efficent?
Eaten as (Pi-complex)
Hydrolyzed in the small intestine (Pi)
Absorbed through 2 mechanisms:
1. Passive diffusion: ~70% efficiency
2. Active transport:
Carrier Mediated: NaPi2b
Stimulated by: Calcitriol (1,25-dihydroxyvitamin D)
Saturable
Which hormones regulate phosphorus and calcium in the kidneys and how is it done?
Increased PTH is released when Pi is high and Ca is low, which causes decreased renal Pi absorption. -
Increased FGF23 is released when Pi is high and causes excretion through urinary excretion and decreases the reuptake of Pi reuptake transporters.
What condition causes Ca-Pi crystals to develop in the the soft tissues with renal impairement (toxicity)?
Hyperphosphatemia
Why would urinary phosphate excretion be a measure of phosphorus status?
- Reflects renal function.
- Urinary losses of Pi increase with PTH. PTH increases when the body needs phosphorus. This decreases renal Pi reabsorption, which is then excreted in the urine.
- This process is unable to occur properly with renal impairment, leading to toxicity.