Vit D Flashcards
Important in
Recommendations
Infant
Child
Adult (18+)
Older (71+)
bone met/calcium and phos homeostasis
vary
400 IU
600
600 IU
800 IU
Source
Dietary sources are
Comes from
Fortified foods includ
made by skin from exposure to sun or preformed in diet
artificially supplemented
Cholecalciferol (D3) or ergocalciferol (D2)
infant formula, milk, cereal
Most VD synthesized via
Length varies on
Process
In the liver
then converted to
1 alpha hydroxylase inc by
Dec by
exposure to UV light
indiv (melanin reduces D3 conversion), intensity of sun
7-dehydrocholesterol to cholecalciferol after light, then to liver
D3 and D2 stored as 25-hydroxy VD (main circulating form)
1,25 dihydroxyVD by 1 alpha hydroxlase
PTH, low serum Ca/Phos
high serum Ca/Phos
1,25 dihydroxyVD binds to
major target tissue
VD binding causes
IC receptors in target tissues and regs gene trxn
GI enterocyte
enterocyte diff/synthesis of Ca receptors, bind proteins, inc Ca/Phos absorption
Def is usually
Causes of deficiency
Inadeq supply
Malabsorption
CLD
CKD
Meds inducing p450 that metabolize VD to inactive forms
asx
lack of sunlight/insufficient intake (young/old esp lack sun)
impair dietary VD absorption (Celiac, panc insuff, bariatric/short bowel syndrome)
dec synth of 25hydroxyVD
def 1 alpha hydroxylase
phenytoin, phenobarbitol, carbamezepine, oxacarbazepine, isioniazid/rifampin, heophylline
Def usually results in
Children w def develop
Ricketts
Def leads to
Osteomalacia def leads to
impaired Ca absorption
rickets/osteomalacia
before epiphyseal fusion
expanding growth plate/grwoth retard
after epiphyseal closure
impaired mineralization of bone matrix proteins
VD def common in
Must have
If def, can get
Adults get
breastfed infants- not enough VD
VD from vit supplement or sun exposure
rickets
osteomalacia
Toxicity
inc intake
occurs w
sx
chronic intox leads to
hypercalciuria/calcemia
inappropriately high dose of supps
confusion, polyuria, A/V, weak
nephrocalcinosis, bone demin, pain
