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NUTR 221: Micronutrients > Vitamin D > Flashcards

Vitamin D Flashcards

1
Q

natural sources of D

A
  • Fatty fish, fish oils, liver, egg yolks
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2
Q

transport form D

A

25(OH)D, calcidiol

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3
Q

active form D

A

1,25(OH)2D, calcitriol

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4
Q

ergocalciferol

A

D2

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5
Q

cholecalciferol

A

D3

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6
Q

2 diff ways to get Vit D

A

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

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7
Q

where is D stored

A

adipose and muscle

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8
Q

which organ converts D to transport form

A

liver

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9
Q

2 places transport D goes

A

kidney (endo) or paracrine/autocrine (cells)

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10
Q

ergosterol to D

A

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

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11
Q

cholesterol to D

A

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

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12
Q

endo path part1

A

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

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13
Q

endo path part 2

A

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

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14
Q

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

A

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

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15
Q

what happens in intestine during endo path

A

increase active transport of Ca and PO4 (ATPase)

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16
Q

what does bone do in endo path

A

stimulate bone calcium reabsorption by stimulating osteoclast (breakdown) activity

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17
Q

what is DBP

A

Vitamin D binding protein, binds while transporting in blood

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18
Q

how long does D circulate

A

1-2 days, then liver converts to 25OH

19
Q

how long does 25OH circulate

20
Q

what does under 30nmol/L 25OH indicate

A

deficiency

21
Q

what does over 150nmol/L 25OH indicate

22
Q

metabolism of D

A

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

23
Q

Vit D and Ca Absorption in cells

A
  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
24
Q

low blood Ca Response, blood

A

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

25
Q

low blood Ca Response, bone

A

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

26
Q

low Ca Response, Kidney

A

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

27
Q

low Ca response, stimulants

A

PTH and Calcitriol stimulate reabsorption of Ca from kidneys to blood

28
Q

low blood Ca response, intestine

A

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

29
Q

EAR and RDA for 1-70 year olds

A

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

30
Q

EAR and RDA for 71+ years

A

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

31
Q

EAR and RDA set at what to maintain?

A

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

32
Q

what does endo society recommend for Vit D intake

A

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

33
Q

what intake of Vit D does cancer society recommend

A

1000 IU in winter

34
Q

food sources of Vit D

A

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

35
Q

milk fortification level

A

5mcg/250mL, OJ and soy too

36
Q

fortification level for margarine

A

2.6mcg/10g

37
Q

mushrooms raw and irradiation

A

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

38
Q

factors relating to decreased sun exposure

A
  • 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
39
Q

D UL

A

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

40
Q

D toxicity

A
  • Over supplementation
  • High blood and urine calcium concentrations
  • Calcium deposits in blood vessels and kidneys
  • CV damage
  • Death
41
Q

new roles of Vit D

A
  • 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
42
Q

D Deficiency

A
  • 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
43
Q

assessment of D

A
  • Serum 25(OH)D concentrations
  • Lower than 20ng/mL = def
  • 21-29ng/mL= insufficiency
44
Q

D absorption

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

NUTR 221: Micronutrients (5 decks)

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