Vit D Flashcards
List all fat soluble vit and where they are found
Fat soluble vit are A,D,E and K and can be found in the fat or fatty tissue and liver
describe absorption of fats
Transporting into blood in chylomicrons — lymphatic system – taken up by hydrolysis
Biological functions of Vit D
Calcium balance
Immunomodulator
Regulates cell growth (anti-proliferation)
Reduces hypertension
what are the 2 ways we can get Vit D
7-dehydrocholesterol in skin from the sun
D3 absorption by digestive tract
How does Vit D increase calcium absorption
In the intestine it can increase from basal 10-15% to 30-80%
In the bones and kidney: induce formation and activation of osteoclasts and increase renal distal tubule reabsorption of calcium
What is the purpose of calcium as a feedback
To increase or decrease formation of Vit D in the kidney
2 conversion that take place to get calcitriol
D3 to 25-OH D3 by liver enzymes
25-OH D3 to calcitriol by kidney enzymes
Most of the effects of Vit D increase or decrease are mediated though?
Gene expression: CPY27B1 + CPY4A1
What are the 3 extra things to consider with Vit D from the sun vs from the diet
The sun Vit D requires UV light to be actived to previt D\
Thermal isomerization (Heat) is needed to convert previt to D3
D3 requires VDBP to enter the bloodstream
CYP27B1
Stim by PTH - highly regulated, gene that increased with low expression of calcium
CYP24A1
Gene that provides Neg feedback for CYP27B or increases when theres to much calcium
Tachysterol
Inactive metabolite of Vit D that decreases Vit D synthesis
How long of sun exposure is needed to obtain enough Vit D
5-15 min from 10AM - 3PM during summer (june-sep)
What factors could affect getting enough sun exposure
Higher latitudes, winter months, time, body temperature, skin color, aging (decreased 7 DHC), sun screen, clothing, obesity (more stored less acessible)
Why would oral supplementation of Vit D3 or injections be prescribed If the person has renal disease
Kidney uses enzymes (CYP27B) and is the synthesizer of Vit D3 to calcitriol. If the kidney isn’t working you’re rather fucked isn;t it
What would chronic liver disease cause
decreases vit D metabolism
Where is vit d2 and d3 found in the diet
D2 is found in plants (mushrooms)
D3 is found in animals (fatty fish, egg yolk, liver)
Fortified food products: Cows milk, yogurt, soy, OJ, Cereal, butter, formula
What is the difference in bioactivity between D2 and D3
D2 contains a Double bound which makes it 20-40% less bioactive than D3
DRI for VIT D: lifestages
Infant: 400 IU
Children: 600 IU
Adults/Prego/Lactating: 600 IU
Over 70: 800 IU
Which groups of people are at risk for inadequacy
Breastfed infant - Mother
Older / Dark skin
Fat malabsorption
Bypass surgery - serum levels may rise
Why is Serum [25(OH)D] > 1,25(OH)2D for indication of vit D status
Serum: long half life 15 days, indicates both sources. (Does not indicate amount stored)
Calcitriol: short half life 15 hr, regulated by PTH/calcium/phosphate. Does not decrease until deficiency is server (always in balance)
IS toxicity possible for Vit D
Not in the skin (regulated)
can be with excessive Vit D 4-5K IU supplementation –> hypercalcemia / soft tissue calcification (deposits of calcium in soft tissue)
Describe what occurs with the following serum levels of 25OHD3; less than 12ng, 12-20ng, >20ng, >50ng
<12 — Vit D deficiency, rickets in children and osteomalacia in adults
12-20 — inadequate for bone and overall health
>20 - adequate
>50 - potential adverse affects
Rickets
Vit D deficiency in children, epiphyseal plates do not close,
hypertrophy of chondrocytes
Symptoms: Soft bones, short, bone deforms
Osteomalacia
Vit D deficiency in adults: poor mineralization of collagen
Symptoms: osteopenia (decrease opacity), increase bone fractures, bone pain
