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NUTR 302 > Vitamin D > Flashcards

Vitamin D Flashcards

1
Q

How is Vitamin D metabolized?

A

fat soluble vitamin so associated with lipids for digestion, absorption and transport.
* absorption associated with bile acids
* transported into circulation via CM
* taken up during hydrolysis of the CM
* Some may be stored in body lipids but most is taken to liver with the CM remnant

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2
Q

Biological functions of vitamin D

A
  • Ca balance in blood
  • regulator of bone mineral metabolism
  • immunomodulator in the inflammatory pathway
  • regulates cell growth having anti-proliferative effects
  • reduces hypertension
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3
Q

What are the 2 main sources to make active vitamin D?

A
  • 7-dehydrocholesterol in skin
  • Vitamin D3 absorption by digestive tract
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4
Q

What is the pathway for making active vitamin D and its role in Ca & P metabolism?

A

concentrations in diet and skin dictate how much converts to 25-OH D3

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5
Q

Major role of active vitamin D

A

Helps maintain normal plasma Ca concentration

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6
Q

Role of active vitamin D in the intestine

A

↑ efficiency of intestinal Ca absorption
* from basal of 10-15% to 30-80%
* also ↑ P absorption

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7
Q

Role of active vitamin D in bones and kidney

A

Along with PTH it induces the formation and activation of osteoclasts & ↑ renal distal tubule reabsorption of Ca

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8
Q

How are most of the effects of active vitamin D induced?

A

Mainly mediated through alerations in gene expression

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9
Q

Differentiate between the structure of vitamin D:
* DHC
* Vitamin D3
* pre vitamin D
* active vitamin D

A
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10
Q

What is the skin form of vitamin D?

A

7 dehydroxycholesterol (DHC)
* steroid structure

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11
Q

What is the dietary form of vitamin D?

A

Vitamin D3
* no hydroxyl units

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12
Q

What is the pre vitamin D form?

A

25 (OH) D or calidiol
* 1 hydroxyl unit

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13
Q

What is the active vitamin D form?

A

1,25 (OH)2 D or calcitriol
* 2 hydroxyl units

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14
Q

What form of vitamin D is this?

A

Vitamin D3

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15
Q

What form of vitamin D is this?

A

pre vitamin D/ 25(OH)D/ calcidiol

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16
Q

What form of vitamin D is this?

A

active vitamin D/ 1,25(OH)2D/ calcitriol

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17
Q

Where is Vitamin D3 converted to calcidiol?

A

in the liver by 25-OH-ase enzyme (CYP2R1 gene)

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18
Q

Where is calcidiol converted to calcitriol?

A

In the kidney by 1𝝰-OH-ase enzyme (CYP27B1 gene)

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19
Q

How is vitamin D transported?

A

VDBP - vitamin D binding protein

20
Q

What can increase gene expression for vitamin D activation in the kidney?

A

PTH can ↑ CYP27B1 gene expression

21
Q

What is the negative feedback vitamin D3 synthesis & metabolism?

A

as plasma ↑ [1,25(OH)2D] the CYP27B1 & CYP24A1 gene expressions ↓
* (CYP27B also suppressed by FGF-23)

22
Q

Toxicity of vitamin D in the skin

A

Impossible
* Vitamin D is photosensitive and degraded by increased exposure to sunlight

23
Q

What is the best measure of vitamin D status?

A

serum 25(OH)D once liver has preformed it
* Biomarker of exposure
* Reflects vit D from cutaneous & food sources (& supplements)
* Long circulating half-life ~15 days
* However does not indicate amount stored

24
Q

Draw the metabolism pathway for vitamin D

A
25
Q

Sun exposure needed for adequate vitamin D intake?

A

Photobiology
* Adequate [25(OH)D] may be obtainable by 5-15 mins sun exposure, 10 AM to 3 PM, during summer
* Higher latitudes & during winter months, UVB photon path length too long for significant vitamin D synthesis

26
Q

What factors effect efficiency of photobiology?

A
  • lattitude
  • geography
  • skin colour
  • ageing
  • sunscreens
  • clothing
  • obesity
27
Q

How does skin colour affect vitamin D synthesis from sunlight?

A

↑skin pigmentation ↓production of pre-vitamin D
* melanin blocks UVB

28
Q

How does ageing affect vitamin D synthesis from sunlight?

A

↓ [7 DHC] in the epidermis & the capacity for the skin to produce vitamin D

29
Q

How does sunscreens affect vitamin D synthesis from sunlight?

A

Diminishs the production of Vitamin D from the skin because sunscreens absorb UV radiation.

30
Q

How does obesity affect vitamin D synthesis from sunlight?

A

Vitamin D is lipid soluble and with increased adipose tissue over time Vitamin D is stored & is less accessible and can build up to toxic levels
* sedentary may be associated with less sun exposure

31
Q

What organs can impair the synthesis of active vitamin D with a disorder?

A

disorders affecting the parathhyroid, liver or kidney

32
Q

What might be prescribed to patients with renal disease in terms of vitamin D?

A

oral supplements or intravenous injections of calcitriol are often prescribed

33
Q

Draw the regulation of vitamin D

A
34
Q

Draw summary of the synthesis and metabolism for Ca, P and vit D

A
35
Q

What are the 2 forms of food sources of vitamin D?

A

It is rare to find naturally occurring active Vitamin D in foods.
* VITAMIN D2: found in plants
* VITAMIN D3: found in animals

36
Q

vitamin D3 vs. vitamin D2

A

The biological activity of Vit D2 is 20-40% that of Vitamin D3
* Can add hydroxy molecules onto D2 by enzymes, so it plugs into same pathway but it is not as potent in helping to regulate Ca absorption and concentrations

37
Q

natural sources of vitamin D

A
  • Fatty fish (tuna, salmon, sardines, mackerel)
  • Egg yolks
  • Beef liver
  • some Mushrooms
38
Q

fortified food products of vitamin D

A
  • Cow’s milk, yogourt, soy beverages
  • OJ
  • Ready to eat cereal
  • Margarine
  • infant formula
39
Q

RDI values for vitamin D

A

Based on AIs because EARs were difficult to determine
* INFANTS: based on the average intake from breast fed and formula fed babies
* CHILDREN: based on children’s needs regardless of exposure to sunlight
* ADULTS: based on serum concentration of 25(OH)D

40
Q

What groups are at risk for vitamin D inadequacy

A
  • Breastfed infants – related to maternal intake
  • Older adults
  • People with limited sun exposure
  • People with dark skin
  • People with fat malabsorption
  • People who are obese or have undergone bypass surgery – serum levels may rise temporarily with weight loss
41
Q

Why is 1,25(OH)2D not a good indicator of vitD status?

A
  • Short half-life ~15 hours, lots of degradation can occur
  • Regulated by PTH, calcium & phosphate
  • Does not decrease until deficiency is severe
42
Q

toxicity of vitamin D from dietary intake

A

Can lead to a state of vitamin D “intoxication” or “hypervitaminosis D”
* Leads to hypercalcemia and eventually soft tissue calcification
* renal & cardiovascular damage
* usually if taking extremely high dose supplements over a long period of time

43
Q

What is the optimal 25-OH-D serum concentrations?

A

80–120 nmol/L
or
30–60 ng/mL

44
Q

Vitamin D status for deficiency, inadequacy, adequate and high levels

A
45
Q

What is the associated disorder of vitamin D deficiency in children?

A

Rickets: If epiphyseal plates have not closed Vitamin D deficiency results in disorganization and hypertrophy of chondrocytes
* Softening of the bones
* Short stature
* Bone Deformities

46
Q

What is the associated disorder with vitD deficiency in adults?

A

Osteomalacia: Poor mineralization of the collagen matrix
* Osteopenia: a decrease in the opacity of the skeleton
* Increased risk of skeletal fractures
* Bone pain
* decreased bone density

47
Q

Causes and consequences of vitD deficiency

A

related to a number of diseases but unknown if it is association or causation

NUTR 302 (20 decks)

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