This is a complicated story; it's where your neph says "Harrumph, it works like this...." and then proceeds to talk for an hour.
I'm not a neph, but I'll try to explain it. Harrumph, it works like this:
Years ago, OTC vitamin preparations often contained vitamin D
2.
Then it was found that vitamin D
3 appeared to perform the same general functions that vitamin D
2 could do, but was three times as potent and had a longer shelf life. As a result, manufacturers of OTC vitamin pills began to reformulate their preparations to include D
3 instead of D
2.
Vitamin D
3, whether it is found in modern OTC vitamin preparations or in your skin produced via UV light, is in an
inactive form, and won't be recognized by your parathyroid glands. This inactive form is processed, once by the liver, and again by the kidneys, to convert it to the
active form of vitamin D
3. That's the form that your parathyroid glands will respond to--and lower your PTH accordingly. But for us ESRD patients, our damaged kidneys can't perform that final activation step on the vitamin D
3 molecule, so it remains in an inactive state, and hence cannot affect our PTH.
Zemplar is a prescription med that is already
activated vitamin D
3. That's what I take to lower my PTH.
At least, that was the type of story you would have gotten from your neph as recently as a few years ago.
But
very recently, there is new evidence that vitamin D
2, which is metabolized through a different pathway than D
3, may also play a useful and
different role in the body from D
3 after all. My nutritionist and neph, always interested in pushing the state of the art if we patients are agreeable, tested my serum D
2 level. Sure enough, it was quite low, despite months and months of Zemplar. As a result, I now take prescription vitamin D
2 by mouth (50,000 units once a week), in addition to the Zemplar IV during dialysis which gives me the activated vitamin D
3.
An upcoming AAKP Conference Call is going to discuss the whole Vitamin D business. I posted details to the "News Articles" section.
Hope this helps.