Vitamin D

Question 1

What is the vitamer produced by plants?

Answer 1

ergocalciferol, D2

Question 2

What is the vitamer produced by animals?

Answer 2

cholecaliferol-D3

Question 3

How is vitamin D derived?

Answer 3

cholesterol synthesis-takes 7-dehydrocholesterol, last step before cholesterol

Question 4

What is the second step of vitamin D synthesis?

Answer 4

photolysis turns 7-dehydrocholesterol into pre-vitamin D

Question 5

What is the third step?

Answer 5

pre-vitamin D is thermoisomerized into D3 (chplecalicferol)

Question 6

What is the fourth step of synthesis?

Answer 6

25-hydroxylase in liver turns into calcidiol

Question 7

What is the fifth step in synthesis?

Answer 7

1a-hydroxylse in kidneys turn it into calcitriol (active form)

Question 8

What is the rate limiting step of synthesis?

Answer 8

isomerization-remains in equilibrium so it will tell body to stop synthesizing it

Question 9

Why can you have too much synthetic vitamin D?

Answer 9

in the D3/D2 form so misses regulatory step

Question 10

What is the main enzyme present in the detoxifying steps and where is it present?

Answer 10

24-hydroxylase-all target tissues

Question 11

What are the classes of hydroxylases?

Answer 11

P450 dependent oxidases

Question 12

Where is the main storage site of Vitamin D?

Answer 12

adipose, but main pool is in plasma

Question 13

How is Vitamin D excreted?

Answer 13

through bile after some additions

Question 14

What is the binding protein in the blood for vitamin D?

Answer 14

Vitamin D binding protein

Question 15

What is special about VDBP compared to other binding proteins?

Answer 15

levels never change, even when active form is low, protein levels remain constant

Question 16

What is the other method that cholecaliferol can be transported?

Answer 16

in lipoproteins

Question 17

How are 1a-hydroxylase and 24-hydroxylase regulated?

Answer 17

availability of calcitriol-reverse effects-if 1a is high then 24 is low

Question 18

What is the primary function of Vitamin D in the body?

Answer 18

maintain blood calcium levels

Question 19

How does vitamin d control blood calcium levels?

Answer 19

promotes reabsorption from kidneys and mobilizes it from bones

Question 20

What is the primary MOA of calcium?

Answer 20

binds to nuclear receptors which activate gene promoters

Question 21

What are some genes that are regulated by vitamin D?

Answer 21

1 and 24 hydroxylases, VDR, calbindin, immune and bone associated genes

Question 22

How does vitamin D act as a gene regulator?

Answer 22

vitamin d receptor is present in nucleus and will change conformation when bound, dimerizes with RXR and binds Vit D response element

Question 23

What are some target tissues of vitamin D?

Answer 23

kidney, bone, parathyroid gland, B-cells in pancreas, pituitary, placenta, mammary glands, skin and immune cells

Question 24

How does Vitamin D influence calcium absorption?

Answer 24

in intestine it will induce more calcium transporters to make a rapid response and then influences calbindin which is a slower response and may have a role in signaling pathways

Question 25

What is calbindin?

Answer 25

calcium binding protein that can bind 4 calciums at once, so if its too high it can sequester it

Question 26

How does vitamin D work with bone?

Answer 26

increases osteoclast function to help mobilize Ca2+, and induces osteocalcin which plays roles in metabolism

Question 27

How does vitamin D work with the immune system?

Answer 27

lower levels means higher infection rates, VDR can induce antimicrobial peptides, no VDR = autoimmunes due to absence of 2 Tregs

Question 28

What is ricketts?

Answer 28

hypocalcemia in children, leads to deformed bowed legs, slower motor development because too much calcium is being mobilized out of bone

Question 29

What is osteomalacia?

Answer 29

ricketts in adults but because of adipose stores it takes far longer

Question 30

What are some theories that were debunked about Vit D supplementation?

Answer 30

decreases MS, cancer, cardiovascular disease and stroke

Question 31

What is the one area Vit D may actually work on and what is the caveat?

Answer 31

Vit D did reduce incidence of T1D but it was 2X tolerable intake and 10X more daily intake

Question 32

What are the symptoms of Vit D toxicity?

Answer 32

weakness, GI, hypercalcemia, headache, kidney stone and calcification of soft tissues