I believe I've had primary hyperparathyroidism for at least 12 years. I am 73. I also have low Vitamin D in the 26 range. Twice over the years and currently I've been prescribed high doses of vitamin D which does raise my Vitamin D level to 40 ng/ml or within normal range, but each time it also raises my PTH. I was given 50,000 IU of D weekly for 2 months and my PTH went up to 140 pg/ml, not down. I'm now on 4,000 daily of Vitamin D and my PTH has gone up to 174.2-147.4. Why would my Vitamin D going up also cause my PTH to go up? My Calcium stays consistent at 10.2-10.5 mg/dl.
The short answer is: You have primary hyperparathyroidism, so Vitamin D is not going to fix your problem. Taking Vitamin D will not be able to overcome the parathyroid tumor. The only way to cure this is with parathyroid surgery, to remove the diseased parathyroid gland(s).
Long answer: A lot of doctors will see low Vitamin D levels and high PTH levels and prescribe Vitamin D in order to “fix” the PTH. This works in one scenario: that of secondary hyperparathyroidism due to Vitamin D deficiency. In that condition, your calcium and Vitamin D are both low, and the PTH is elevated. This is not caused by a parathyroid tumor. The PTH is high because the parathyroid glands are working hard to get the calcium level up to normal. When your Vitamin D is low, your intestines can have difficulty absorbing calcium, so your parathyroids work harder to get the calcium up. Taking Vitamin D helps your intestines absorb calcium, so it raises your blood calcium level and eases the strain on the parathyroids - so they need to make less PTH.
In your situation, though, the underlying problem is not low Vitamin D. The underlying problem is with your parathyroids. Parathyroid disease actually causes low Vitamin D, because it stimulates the conversion of inactive Vitamin D (the form we measure) to active Vitamin D (the form we don’t usually measure). Taking more Vitamin D is not going to fix this problem, and may make it worse, since Vitamin D can raise your calcium levels further. PTH levels rise and fall during the normal course of primary hyperparathyroidism, whether you are taking Vitamin D or not - this is what is happening in your case.
Note that Vitamin D and PTH are pretty tricky! Low Vitamin D can lead to high PTH levels, but high PTH levels can also cause low Vitamin D! How do you know which one is causing the other? The key is the calcium level. If the calcium is LOW, then the low Vitamin D is causing the high PTH (by way of causing low calcium). If the calcium is HIGH, then the PTH is causing the low Vitamin D. Your calcium levels are high for your age, so your levels are consistent with primary hyperparathyroidism, and thus the PTH is causing the Vitamin D to be low. Taking Vitamin D will not fix that.