Vitamin D

Question 1

Calcitrol

Answer 1

Active form of vitamin D

aka 1-alpha, 25-dihydroxyvitamin D3

Question 2

Calcidiol

Answer 2

Inactive form of vitamin D

25-hydroxyvitamin D3

Question 3

Cholecalciferol

Answer 3

The inactive form of vitamin D; from the skin

Question 4

How do you convert IU to mcg?

Answer 4

40 IU = 1 mcg of vitamin D

Question 5

Food sources of vitamin D

Answer 5

Cod Liver Oil
Swordfish
Salmon
Tuna
OJ fortified
Milk-fortified
Milk alternatives-fortified

Question 6

(TRUE/FALSE)

The government mandates that foods are fortified with vitamin D.

Answer 6

FALSE, it is a VOLUNTARY fortification and it’s about 100 IU/cup

Started back in the 1930s, due to the onset of rickets

Question 7

Where is 7-dehydrocholesterol stored?

Answer 7

Within the sebaceous glands of the skin

Question 8

How do we biosynthesize vitamin D from the sun?

Answer 8

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.

Question 9

25-hydroxylase

Answer 9

An enzyme in the liver that acts on cholecalciferol (adds a hydroxyl group at the 25 place), forming 25-hydroxyvitamin D3 (CALCIDIOL)

Question 10

Ergocalciferol vitamin D2

Answer 10

form that comes from diet or supplementation

Question 11

Briefly explain the absorption of vitamin D

Answer 11

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.

Question 12

What are the functions of vitamin D?

Answer 12

1. Calcium homeostasis
2. Gene expression (acting like a steroid hormone)

Question 13

(TRUE/FALSE)

Active vitamin D acts as a steroid hormone and regulates gene expression.

Answer 13

TRUE

There are a myriad of pleiotropic effects are seen as a result of genomic functions, acting as a regulator of gene expression

Question 14

How many genes in WBCs are targets of vitamin D?

Answer 14

169 genes

Question 15

VDR

Answer 15

Vitamin D receptor within the nucleus of cells

It is a nuclear receptor

Question 16

Heterodimer

Answer 16

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

Question 17

(TRUE/FALSE)

No other tissues in the body can up regulate gene expression through VDRE process.

Answer 17

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

Question 18

Why has vitamin D been shown to play such an important role in cell differentiation and mediating the risk for chronic diseases?

Answer 18

Vitamin D and it’s role with regulation of gene expression

Question 19

What binds to the VDR?

Answer 19

Calcitriol enters into the nucleus and binds to the VDR

Question 20

Vitamin D toxicity

Answer 20

Never observed with sunlight, only with high levels of pharmacological doses or supplementation

Causes hypercalcemia

Question 21

When has vitamin D toxicity observed?

Answer 21

Daily doses of greater than 50,000 IU

Question 22

Toxicity is very unlikely in healthy people at intake level lower than XXXXX IU/day.

Answer 22

10,000 IU/day

Question 23

(TRUE/FALSE)

It is recommended that individuals stay within the upper tolerable intakes for vitamin D and not to exceed these levels.

Answer 23

TRUE

For adults, 19 years and older, that would be 4,000 IU (100 microgram/day) daily (set by the FNB)

Question 24

What is the best assessment of vitamin D status for clinical settings?

Answer 24

Liquid chromatography, because it is faster and more reliable

Question 25

(TRUE/FALSE)

There is considerable variability among the various assays available for vitamin D status.

Answer 25

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

Question 26

<30 nmol/L (<12 ng/mL) vitamin D status

Answer 26

Associated with vitamin D deficiency, leading to rickets in infants in children and osteomalacia in adults

Question 27

30 to <50 nmo/L (12 to <20 ng/mL) vitamin D status

Answer 27

Generally considered inadequate for bone and overall health in healthy individuals

Question 28

> or equal to 50 nmol/L (> equal to 20 ng/mL) vitamin D status

Answer 28

Generally considered adequate for bone and overall health in healthy individuals

Question 29

> 125 nmol/L (50 ng/mL) vitamin D status

Answer 29

Emerging evidence links potential adverse effects to such high levels, particularly >150 nmol/L (>60 ng/mL)

Question 30

How do you convert 1 nmol/L to X ng/mL

Answer 30

1 nmol/L = 0.4 ng/mL

Question 31

What is the UL for vitamin D?

Answer 31

4,000 IU/day for all adults, set by FNB