Vitamin D
Human and cow milk are both naturally high in vitamin D.
False
Morbidly obese patients tend to have elevations in serum 25 hydroxyvitamin D.
False (vitamin D cells sequestered in the fat cells)
Children with rickets will have
poor appetite, retarded growth, muscular weakness, bone pain, delayed tooth eruption, swollen joint, rachitic rosary, forwarded breast bone, spine curvature, poor growth
Melanin
Dark pigment that prevent UV light comes in and prevent the activation of vitamin D3
This form of vitamin D has apparently low bioavailability, so manufacturers are phasing it out of supplements.
Ergocalciferol
Small changes in dietary vitamin D translates to large changes in serum vitamin D.
False
The committee that set the new RDAs for vitamin D considered (accounted for) the vitamin's ability to prevent cardiovascular disease and cancer.
False (no OPTIMAL LEVEL for vitamin D so far) <30 nmol/L= deficient 30-50nmol/L=sufficient >50nmol/L =sufficient but no sign of benefit 2010 DRI suggest, serum 25OH vitamin D3 >30nmol/L =good!
Weekly doses of 50,000 IU vitamin D are unsafe and should not be administered more than twice.
False (50,000IU for 8 weeks is considered safe > it is valuable in treating elderly, pts with liver failure nephrotic system, severe intestinal malabs) 10,000 is safe for 16 weeks as well)
Too much sun exposure can result in a toxic level of vitamin D.
False (the innert photoproduct do not hurt us)
Who will have serum 25OH vitamin D measure?
Intestinal malabsorption syndrome limited exposure to sun light -limited ability to take oral vitamin D suppl -aged and homebound patient -skin pigmentation
Exposure to the sunlight is equivalent to about 10,000 IU of vitamin D.
True
Vitamin D3 is better absorbed than vitamin D2.
True
Your grandmother's ability to photoconvert vitamin D in her skin is less efficient than yours.
True
The upper limit of dietary vitamin D is 100 micrograms.
True (4000IU)
What are the latest suggestions for sun exposure to get enough vitamin D without damage to the skin?
expose the hands, face and arms to sunlight for a period equal to 25% of the time that it would take to cause a light pinkness to the skin (=1MED-Minimum Erythemal Dose)
Signs of vitamin D toxicity (hypervitaminosis D)
hypercalcemia, hyperphosphatemia, & hypercalciuria.
The mode of vitamin D action is . . . . .
paracrine autocrine endocrine
Best way to detect vitamin D deficiency for patients in nursing home
serum 25 D will be low and PTH will be high Low serum 25D due to -poor dietary intake -poor exposure to sunlight particularly in the cold north in the winter -decreased abs from the GI tract -dec ability of skin to activate -dec ability of kidney and liver to hydroxylate vitamin D precursors -anticovulsant and steroid drugs disrupt vit D metabolism
Vitamin D functions
-Increase bone turnover -Inc intestinal calcium abs via the active saturable route (calbindin) -high vitamin 1,25OH Vit D3>inc serum calcium > feed back to dec synthesis of PTH
Secondary hyperparathoridism may be caused by...
-Rickets (health problem in some US inner cities, poor mineralization of the osteoid (bone matrix) on trabecular bone surface) -Osteomalacia
T/F Statements regarding vitamin D
-Target levels of serum vitamin D for optimal health are well established (F) True: -No legislation in the US mandating that vitamin D be added in milk -Vitamin D requirements in adults increased a small amount over the previous DRIs -Vitamin 's role in preventing cancer is not clearly established -Most foods contain little to no vitamin D
STATEMENTS about Vitamin D
-almost no dermal potoconversion of vit D in january in boston
Who is at risk for a vitamin D deficiency?
-breastfed infants -older adults (canot synthesize vit D efficently> due to the ability to photoconvert declines) -people with limited sun exposure -People with dark skin -fat malab (vit is fat soluble- liver disease, cystic fibrosis, crohns disease) -obese/undergone gastric bypass surgery -Steroid (on corticosteroid medication like prednisone-will reduce Ca abs, and impair vit D metabolism) -alcoholics,liver/renal disease)
PTH
-hypervalvemia suppresses PTH secretion -Hypocalcemia stimulates PTH secretion -PTH stimulates bone resorption -PTH activates vitamin D
Vitamin D metabolism
1.the cholesterol underneath the epidermis and dermis called 7 dehydrocholesterol. 2. exposed to UV light, 7dehydrolesterol is converted to previtamin D3 3. at body temp, previtamin D3 is converted to vit D3. 4. food that we consume have vitamin D3 (cholecalciferol)- not active, goes to liver. 5. The 25hydroxylase in liver add OH to 25 carbon > 25 OH D3 (calcidiol)-not active. 6. 25OHD3 travels to kidney > it got hydroxylated at 1 position by the rena 1 alpha hydroxylase (this hormone is activated by the PTH) > 1,25 OH VIT D3 (calcitriol)
Unit of measure for vit D
1ug Vit D=40 IU Vit D = 1USP unit vitD
Cholesterol found in the dermins and epidermis
7 dehydrocholesterol> when expose to UV >previtamin D3
Bone remodeling
=bone resorption by osteoclast and bone formation by osteoblast
the classic target tissues for vitamin D are:
Bone, Kidney, Gut
Measuring this form in the serum gives an excellent indication of vitamin D status.
Calcidiol (or 25 hydroxy cholecalciferol)
This form of vitamin D is the biologically active form
Calcitriol (or 1,25 dihydroxycholecalciferol)
To synthesize this form of vitamin D, we need a healthy kidney and liver.
Calcitriol (or 1,25 dihydroxycholecalciferol)
This form of vitamin D will most likely cause hypercalcemia and hypercalciuria if administered orally, so we don't typically administer it to healthy individuals
Calcitriol (or 1,25 dihydroxycholecalciferol) This form of vit D is too active to healthy individuals
Renal patients are vitamin D deficient because they:
Cannot activate this vitamin
This form of vitamin D is produced by the action of UV light on the skin.
Cholecalciferol (vitamin D3)
Which food is richest in vitamin D (per serving)?
Milk from the Big Y grocery store Cheese, icecream-not good source of vitamin D Only milk fortified vit D is good source
Serum alkaline phosphatase (SAP)
an elevation reflects activation of osteoblasts> its seen when there is an increased bone destruction and remodeling. Increased in ricket or osteomalacia patients. *High the enzyme> the worse the deficiency
