Vitamin D

Question 1

natural sources of D

Answer 1

• Fatty fish, fish oils, liver, egg yolks

Question 2

transport form D

Answer 2

25(OH)D, calcidiol

Question 3

active form D

Answer 3

1,25(OH)2D, calcitriol

Question 4

ergocalciferol

Answer 4

D2

Question 5

cholecalciferol

Answer 5

D3

Question 6

2 diff ways to get Vit D

Answer 6

Intake: UVB + skin -> 7-dehydrocholesterol -> previtamin D3 -> vitamin D
intake: diet (D2 or D3)

Question 7

where is D stored

Answer 7

adipose and muscle

Question 8

which organ converts D to transport form

Answer 8

liver

Question 9

2 places transport D goes

Answer 9

kidney (endo) or paracrine/autocrine (cells)

Question 10

ergosterol to D

Answer 10

ergosterol (previt D2), yeast/fungi, -> irradiation UV = ergocalciferol D2

Question 11

cholesterol to D

Answer 11

Cholesterol, in skin -> 7-dehydrocheolesterol, in skin + UVB -> previt D2 + thermal isomerization = Vitamin D3/cholecalciferol

Question 12

endo path part1

Answer 12

Vitamin D3/cholecalciferol (in chylomicron/blood, bound to DBP) -> 25-OH D/ calcidiol (in liver) -> blood + DBP -> kidney

Question 13

endo path part 2

Answer 13

In Kidney:
1. 24-hydroxylase (+ high calcitriol) -> 24,25 (OH)2 D -> released into blood +DBP = various tissues
2. 1-hydroxylase (+PTH and low Calcium, -P) -> 1,25(OH)2 D/calcitriol -> 24-hydroxylase (+high calcitriol) -> 1, 24, 25- (OH)2 D => calcitroic acid

Question 14

what happens in endo path when high PTH low calcium or low FGF-23 (low P)

Answer 14

1-hydroxylase makes plasma 1,25(OH)2 D

Question 15

what happens in intestine during endo path

Answer 15

increase active transport of Ca and PO4 (ATPase)

Question 16

what does bone do in endo path

Answer 16

stimulate bone calcium reabsorption by stimulating osteoclast (breakdown) activity

Question 17

what is DBP

Answer 17

Vitamin D binding protein, binds while transporting in blood

Question 18

how long does D circulate

Answer 18

1-2 days, then liver converts to 25OH

Question 19

how long does 25OH circulate

Answer 19

1 month

Question 20

what does under 30nmol/L 25OH indicate

Answer 20

deficiency

Question 21

what does over 150nmol/L 25OH indicate

Answer 21

toxic

Question 22

metabolism of D

Answer 22

25OH -> 1-hydroxylase = 1,25OH2/cacitriol (active) -> blood

Question 23

Vit D and Ca Absorption in cells

Answer 23

1. 1,25 (calcitriol) enters cell + bind to Vit D Receptor (VDR)
2. 1,25-VDR enters nucleus
3. Bind DNA
4. Transcription
5. Translate Ca binding proteins in enterocyte: Ca channel (TRPV6), ATPase
6. Calbindin open Ca channel in BBM
7. Increase Ca absorption (active transport/ATPase)
8. Energy required for Ca to be on basolateral side = ATPase

Question 24

low blood Ca Response, blood

Answer 24

Blood: low calcium -> signals PTH gland to release PTH into blood

Question 25

low blood Ca Response, bone

Answer 25

Bone: PTH in blood stimulates bone mineral breakdown/resorption to release calcium into blood

Question 26

low Ca Response, Kidney

Answer 26

Kidney: PTH stimulates kidneys to make 25OH D +1-hydroxylase = calcitriol (active)

Question 27

low Ca response, stimulants

Answer 27

PTH and Calcitriol stimulate reabsorption of Ca from kidneys to blood

Question 28

low blood Ca response, intestine

Answer 28

Calcitriol released from kidney to intestine: promote Ca absorption through BBM, calbindin transport in cell, release Ca into blood (ATPase)

Question 29

EAR and RDA for 1-70 year olds

Answer 29

EAR= 400 IU (10mcg) DRA= 600 IU (15mcg)

Question 30

EAR and RDA for 71+ years

Answer 30

EAR= 400 IU (10mcg) RDA= 800 IU (20mcg)

Question 31

EAR and RDA set at what to maintain?

Answer 31

25OHD- 40nmol/L and 50nmol/L for bone health

Question 32

what does endo society recommend for Vit D intake

Answer 32

25OHD serum levels at 75nmol/L to support other functions, immunity

Question 33

what intake of Vit D does cancer society recommend

Answer 33

1000 IU in winter

Question 34

food sources of Vit D

Answer 34

milk, cheddar cheese, yogurt, eggs, liver, salmon, chicken

Question 35

milk fortification level

Answer 35

5mcg/250mL, OJ and soy too

Question 36

fortification level for margarine

Answer 36

2.6mcg/10g

Question 37

mushrooms raw and irradiation

Answer 37

raw = 0.09-.63/100g UV = 20-25mcg/100g

Question 38

factors relating to decreased sun exposure

Answer 38

- Latitude over 40 degrees Vit D winter - Pollution - Clouds - Work/ stay indoors 10-3 - Most Canadians need dietary/supplemental Vit D in winter (SK= Oct-March), some may need all year - Time of day, skin colour, age, obesity, protective clothing or sunscreen

Question 39

D UL

Answer 39

9 and older = 4000IU bc 5000 shown to be safe, UF factor 1.25, serum levels over 150nmol/L not shown to be protective, maybe harmful

Question 40

D toxicity

Answer 40

- Over supplementation - High blood and urine calcium concentrations - Calcium deposits in blood vessels and kidneys - CV damage - Death

Question 41

new roles of Vit D

Answer 41

- DRIs not based on these new roles - Evidence inconclusive for any other benefits except bone health - 1,25 D is transcription factor, signals transcription of many genes -> cell differentiation and growth - Good evidence for reducing risk of respiratory disease and cancers

Question 42

D Deficiency

Answer 42

- Widespread worldwide - Rickets-> children, failure to bone mineralize - Osteomalacia-> adults: failure to mineralize already formed bone - Malabsorptive disease that reduced intestinal absorption of fat - Supplement breast-fed infants and others with impaired Vit D absorption

Question 43

assessment of D

Answer 43

- Serum 25(OH)D concentrations - Lower than 20ng/mL = def - 21-29ng/mL= insufficiency

Question 44

D absorption

Answer 44

- Vit D requires no digestion o Absorbed from micelle by passive diffusion - Jejunum (middle) - In chylomicron for transport in lymph, then blood