Vitamin D Flashcards
Calcitrol
Active form of vitamin D
aka 1-alpha, 25-dihydroxyvitamin D3
Calcidiol
Inactive form of vitamin D
25-hydroxyvitamin D3
Cholecalciferol
The inactive form of vitamin D; from the skin
How do you convert IU to mcg?
40 IU = 1 mcg of vitamin D
Food sources of vitamin D
Cod Liver Oil
Swordfish
Salmon
Tuna
OJ fortified
Milk-fortified
Milk alternatives-fortified
(TRUE/FALSE)
The government mandates that foods are fortified with vitamin D.
FALSE, it is a VOLUNTARY fortification and it’s about 100 IU/cup
Started back in the 1930s, due to the onset of rickets
Where is 7-dehydrocholesterol stored?
Within the sebaceous glands of the skin
How do we biosynthesize vitamin D from the sun?
We store 7-dehydrocholesterol in the skin and when UV light hits the skin, pre-vitamin D3 is formed.
Pre-vitamin D then thermally isomerizes to form vitamin D3 cholecalciferol.
From here, the cholecalciferol is going to leave the skin bound to vitamin-D binding protein, and is then going to go the liver.
25-hydroxylase
An enzyme in the liver that acts on cholecalciferol (adds a hydroxyl group at the 25 place), forming 25-hydroxyvitamin D3 (CALCIDIOL)
Ergocalciferol vitamin D2
form that comes from diet or supplementation
Briefly explain the absorption of vitamin D
Similar to other fat-soluble vitamins:
The fat-soluble vitamins are going to be incorporated into the MICELLE, coated with bile acids and they also contain TGs and cholesterol.
The micelle will be brought to the interface of the brush border membrane, and they enter the enterocytes.
Once inside, the fat-soluble vitamins, TG, and cholesterol will be incorporated into the CHYLOMICRON.
The CM exits the enterocyte through the basolateral membrane and enters the lymphatic system.
What are the functions of vitamin D?
- Calcium homeostasis
- Gene expression (acting like a steroid hormone)
(TRUE/FALSE)
Active vitamin D acts as a steroid hormone and regulates gene expression.
TRUE
There are a myriad of pleiotropic effects are seen as a result of genomic functions, acting as a regulator of gene expression
How many genes in WBCs are targets of vitamin D?
169 genes
VDR
Vitamin D receptor within the nucleus of cells
It is a nuclear receptor
Heterodimer
RXR & VDR + Calcitriol
Which they then, bind to the VDRE (vitamin D response element), activating the expression of that gene, leading to changes in protein synthesis
(TRUE/FALSE)
No other tissues in the body can up regulate gene expression through VDRE process.
FALSE
Thousands of genes have been identified in various tissues, where vitamin D binds to its nuclear receptor and heterodimerizes with the RXR receptor and increases the expression of certain genes
Why has vitamin D been shown to play such an important role in cell differentiation and mediating the risk for chronic diseases?
Vitamin D and it’s role with regulation of gene expression
What binds to the VDR?
Calcitriol enters into the nucleus and binds to the VDR
Vitamin D toxicity
Never observed with sunlight, only with high levels of pharmacological doses or supplementation
Causes hypercalcemia
When has vitamin D toxicity observed?
Daily doses of greater than 50,000 IU
Toxicity is very unlikely in healthy people at intake level lower than XXXXX IU/day.
10,000 IU/day
(TRUE/FALSE)
It is recommended that individuals stay within the upper tolerable intakes for vitamin D and not to exceed these levels.
TRUE
For adults, 19 years and older, that would be 4,000 IU (100 microgram/day) daily (set by the FNB)
What is the best assessment of vitamin D status for clinical settings?
Liquid chromatography, because it is faster and more reliable
(TRUE/FALSE)
There is considerable variability among the various assays available for vitamin D status.
TRUE
This means that compared with the actual concentration of 25(OH)D in a sample of blood serum, a falsely low or falsely high value may be obtained depending on the assay or laboratory used
The two most common methods being antibody-based and liquid chromatography based
<30 nmol/L (<12 ng/mL) vitamin D status
Associated with vitamin D deficiency, leading to rickets in infants in children and osteomalacia in adults
30 to <50 nmo/L (12 to <20 ng/mL) vitamin D status
Generally considered inadequate for bone and overall health in healthy individuals
> or equal to 50 nmol/L (> equal to 20 ng/mL) vitamin D status
Generally considered adequate for bone and overall health in healthy individuals
> 125 nmol/L (50 ng/mL) vitamin D status
Emerging evidence links potential adverse effects to such high levels, particularly >150 nmol/L (>60 ng/mL)
How do you convert 1 nmol/L to X ng/mL
1 nmol/L = 0.4 ng/mL
What is the UL for vitamin D?
4,000 IU/day for all adults, set by FNB
