Spinach has the worse calcium bioavailability
Same reason as with Iron, due to oxalate that bind to the free Ca and Fe and won't release it
What inhibits Ca bioavailability?
- Phytates (beans)
- Polyphenols (tea/coffee)
- Oxalate (Spinach)
When is absorption of Ca increased? (4)
- 1) low Ca diet
- 2) Pregnancy
- 3) Lactation
- 4) growth
Ca utilizes what kind of absorption?
What type of pH is needed to absorb Ca?
If the pH is high, what will bind and sequester Ca?
Phosphate to form insoluble calcium phosphate
When Ca is low, what absorption path is used?
Are Paracellular and Transcellular absorption Vit. D dependent/Ind.?
- Paracellular: independent
- Transcellular: dependent
What form of Vit. D is necessary for transcellular absorption?
Calcitriol 1,25 (OH)2D3
Where are TRPV5/6 located and what is their function?
- TRPV5 = kidney
- TRPV6 = liver
- **both absorb Ca for transcellular absorption
- **transcribed by calcitriol in the nucleus
What binds Ca to keep it unbound from Phosphate?
What are the two basolateral transporters of Ca?
- Ca-ATPase - primary active transport
- NA/CX - Secondary active transport
How is Vit. D3 formed and what is it called?
7-dehydrocholesterol + UV light = Cholecalciferol (Vit. D3)
What contains vit. D2 and what is it called?
- Found in plants/plankton
What are the three forms of vitamin D called?
- Vitamin D: Calcitriol
- Vitamin D2: ergocalciferol
- Vitamin D3: Cholecalciferol
What must general Vitamin D be transformed to in the liver and kidney?
- Liver: Calcidiol
- Kidney: Calcitriol
What happens with the PTH with increased vitamin D and increased Ca?
PTH is inhibited
Where does the PTH work, kidney or liver?
Kidney to produce Calcitriol
What are the effects of calcitriol in the kidney? (4)
- Increase intestinal Ca absorption
- Mobilize Ca from bone
- increase renal absorption of Ca
- decrease Renal excretion of Ca
What causes calciuria?
- Excess NaCl
- Problem with older women due to loss of estrogen
What can counterbalance the NaCl effect ad Calcuria?
How does the thyroid gland effect Ca?
- When Ca is high, the thyroid gland releases calcitriol
- Calcitriol stops Ca bone mobilization
- Allows Vit. D to be used in other body systems
What part of the bone is most susceptible to Osteo.?
Trabecular (center, spongy)
When does Osteopenia become osteoporosis?
When BMD <-2.5
What happens to Ca and Vit. D levels with aging?
They both decrease
At what age should we worry about a low BMD?
30, b/c this is when we should be at our peak BMD
What are the three risk factors for osteoporesis?
- 1) Age
- 2) BMD level low at age 30
- 3) Menopause
What should you supplement with if you suffer from osteoporosis?
Vitamin D + Calcium
Why is exercise important to inhibit osteoporosis?
It increases bone density