How come Vitamin D increases resorption and yet cause osteomalacia? - USMLE Forums
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Old 12-27-2010
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Bones How come Vitamin D increases resorption and yet cause osteomalacia?

Vitamin D increases bone resorption in Ca+ and PO4 (calcium and phosphate)

beside this also decrease in Vitamin D will cause rickets (kids) and osteomalacia (adult)


how this???
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Old 12-27-2010
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Default just found this explanation

Vitamin D effects on bone; Resorption or what?

Vitamin D effects on bone; Resorption or what?
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Old 12-27-2010
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vitamin D increase Ca and PO4 resorption from your GIT not your bone
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Old 12-27-2010
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Quote:
Originally Posted by nomadsam View Post
vitamin D increase Ca and PO4 resorption from your GIT not your bone

DEAR there is difference between REABSORPTION AND RESORPTION

REABSORPTION : PROCESS IN SMALL INTESTINE

BUT RESORPTION : is the process by which osteoclasts break down bone and release the minerals
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Old 12-27-2010
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Quote:
Originally Posted by kemoo1985 View Post
DEAR there is difference between REABSORPTION AND RESORPTION

REABSORPTION : PROCESS IN SMALL INTESTINE

BUT RESORPTION : is the process by which osteoclasts break down bone and release the minerals
Excessive resorption of bone = loss in tensile strength of bone = osteomalacia / rickets (depending on age)

Normally this is due to decreased serum Ca levels, in this case due to decreased Vit D. So in the sense, the body is trying to raise serum Ca levels.
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Old 12-27-2010
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Sorry for my incorrect use of terminology.

I'm guessing your confusion lies in the fact that if vit D is responsible for promotion of absorption of Ca in GIT and reabsorption of Ca in kidneys, then why does it also promote osteoclast activity.

If someone can clear this up, I'd appreciate it also. I'm seeing conflicting reports on whether vit D really does promote osteoclasts..
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Old 12-27-2010
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Default Both deficiency and excess can cause bone resorption!

Simply put: Vitamin D level needs to be within the normal range for all things to be OK. Too little vitamin D means not enough Ca is being absorbed from the intestine, and you end up with rickets or osteomalacia. Too much vitamin D goes crazy and ends up eating out the bone, causing osteopenia.
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Old 12-27-2010
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In my opinion, vitamin D does not induce bone resorption. Actually, I'm quite sure that it induces mineralization of the bone through increasing calcium transport through membranes.

Once I read that, in non-physiologic concentrations - I mean, in extreme concentrations -, it really enhances osteoclastic activity, but I'm not sure about that.


To sum up, vitamin D induces bone mineralization through its effect on the absorption in the GI tract, which enhances serum calcium.
(In fact, vit. D has a mineralization effect even without incrasing serum calcium.)



(Sorry for grammar - or any other - mistakes. As you can notice, I'm not american).
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Old 12-27-2010
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Quote:
Originally Posted by kemoo1985 View Post
Vitamin D increases bone resorption in Ca+ and PO4 (calcium and phosphate)

beside this also decrease in Vitamin D will cause rickets (kids) and osteomalacia (adult)


how this???
PTH increases Vit D. Vit D increase Reabsorption of Calcium and Phosphate in the gut. PTH increases calcium reabsorption in the kidney, and increases resorption of bone (that is, the bone is being eaten up by osteoclast to release the phosphates and calcium into the serum). If you mean VitD in relation to PTH increases bone resorption then that would make sense. But not vitD. It's PTH, I believe, that can cause osteomalacia. But haven't heard of Vit D doing this.
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Old 04-28-2011
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so it seems still an enigma ..... LOL

nobody can explain sufficiently....

bottom line.....just remember that vit-d excess and deficiency can cause

decreased BMD..
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Old 04-28-2011
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Quote:
Originally Posted by ikrimachoudry View Post
so it seems still an enigma ..... LOL

nobody can explain sufficiently....

bottom line.....just remember that vit-d excess and deficiency can cause

decreased BMD..
Did you read my post here
Vitamin D effects on bone; Resorption or what?
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Old 03-21-2013
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Default Enigma solved

It's pretty simple . Vitamin D's function is promote bone mineralization so in order to promote "new" bone mineralization it stimulates resorption of "old bone " to increase serum levels of Ca++ and phosphate and use them for the new bone.
So in deficiency there is no bone turnover so that could lead to rickets...
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Old 03-22-2013
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Default hi.

i was myself confused a little about this issue when i read it on goljan.

from what i understand:
although vitD primarily reabsorbs ca and po4 from the git ,which in turn leads to mineralization ,in this way it causes bone deposition,

but at higher concentrations vit D behaves like PTH and cause one resorption .this is what i get from the explantion given in goljan.

now how does that sound???
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Old 04-07-2013
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Correct Answer

Maybe the cause of all this misunderstanding is First Aid, sometimes they tend to make some mistakes, according to the 2012 FA errata in page 99 about vitamin D in function instead of saying "Increases bone resorption" you have to change it to "increases bone mineralization".

If you want to make sure check the 2012 First Aid errata, page 99.
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Old 04-11-2013
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Smile Vitamin D function and deficiency!!

Vitamin D in its active form i,e 1,25 dihydroxycholecalciferol, it has effects on three organs, intestine, bone and kidney.

In bone: it helps in remodeling process, it activates osteoblasts to cause mineralization, and it activates osteoclasts by RANK Logan's to cause resorption (removal of calcium from bone). This is a normal process which makes bone a dynamic tissue ( remember we are going to get entirely new skeleton every 10 years!!).


In intestine: it induces a gene which code for calbindin protein, calbindin in intestine helps to absorb calcium and phosphate from diet.


In kidney: it helps to reabsorb calcium and phosphate.


PTH: increase whenever there is low calcium levels there by PTH induce 1 alpha hydroxylase in kidney which hydroxylate vitamin D into its active form thereby bring back normal calcium levels.


In rickets (children), decreased mineralization, and osteomalacia (in adults) there will be demineralization due to low vitamin D levels, in adults, during the deficiency if vitamin D, the osteoclastic activity will be predominant under the influence of PTH to maintain calcium levels, this lead to bone softening and pathological fractures!!


Hope this helps


Dr Mungli
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  #16  
Old 04-13-2013
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from what i remember, and i think its been touched on earlier. it's all about bone remodeling. just because vitamin D causes Bone Resorption is only half the story. to make new bone, u need calcium from somewhere. that calcium comes from vitamin D's action on inc Ca++ reabsorprtion from the intesting, and increased resorption from preexisting bone.

then that calcium is used to mineralize new (more solid) bone. without the vitamin D, ur not gonna be able to get enough Calcium to mineralize new bone. does that make sense?
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