Kyle I am not a scientist or a doctor. You can keep checking back to see if anyone else answers your question with different information.
I have been a member of the VDC for a long time which means I have read everything they have posted for years now. Unfortunately there is not a lot of information on hypercalcemia and Vitamin D. There is only hypercalcemia caused by taking too much Vitamin D in normal people.
Having said that I just tried to answer someone else the other day, so you may want to scroll down ten questions counting yours to “Alfacalcidol for Vitamin D deficiency?…” and read what I wrote there. Next the VDC had this on their blog https://www.vitamindcouncil.org/blog/randomized-controlled-trial-vitamin-d-supplements-carry-only-slight-risk-in-sarcoidosis/. Unless you are a member it is locked and you cannot read it but you CAN read the comments at the end of the blog posting! I did find the study in its entirety at http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3808783/ . I realize you do not have sarcoidosis but the point of the study was worry of supplementation would cause issues and basically it did not. (Do keep in mind that overall this study did not give enough Vitamin D such as what we recommend at this website. Levels in the study were about 30ng/ml and we recommend 50ng/ml.)
In another study “Vitamin D supplementation in primary hyperparathyroidism, not a bad idea?”, it also turned out not to be a bad idea to supplement. In this article the VDC recommended that the “condition and supplementation regimen is closely monitored by a qualified health professional”. Makes perfect sense to me.
Vitamin A toxicity can be a reason for hypercalcemia and I mentioned it in the other answer. Per chance do you or have you ever taken a multi vitamin or some other form of Vitamin A that is “preformed” and not the natural form of beta carotene?
Did anyone ever check your 1.25 OHD levels which is different than 25OHD-Vitamin D? I am not saying that they had to, just asking.
That’s all I have. If you have any more questions just ask!
You might try this:
Take 600mg Magnesium salt (magnesium citrate, chelate or other) plus 1mg-1.5mg vitamin K2 mixed (menaquinone 7 and menaquinone 4) for three to four weeks before any supplementation with vitamin D3. If possible have your serum calcium levels rechecked to see if they have lowered.
At any rate taking the vitamin D3 along with the magnesium plus K2 should avoid any rise in serum calcium. Of course it is best to have the levels rechecked.