This study will look at the effect of 2 treatment regimens that contain vitamin D in a six-month treatment trial of patients with PHPT who are vitamin D deficient. Patients will be assigned randomly to one of 2 regimens, and will be followed with tests of their blood, urine and bones. This study should provide important information on the effect of vitamin D therapy in patients with PHPT. In addition, data from this study will guide physicians as to how best to treat their patients who have PHPT and vitamin D deficiency.

Primary hyperparathyroidism (PHPT) is a common disease in which the parathyroid glands produce excessive amounts of parathyroid hormone (PTH), which regulates calcium levels. In primary hyperparathyroidism, high levels of PTH remove too much calcium from bones and deposit the excess calcium in the blood, which is then filtered into the urine by the kidneys. Bone health is threatened by the excess calcium loss which weakens the structure of the bones.

Many patients with primary hyperparathyroidism also have low vitamin D (25OHD) levels which is thought to further impair bone health. Recent medical guidelines recommend treating patients with primary hyperparathyroidism who have low vitamin D levels with oral vitamin D but the optimal vitamin D dose and rate of repletion is unclear. It is, therefore, important to determine if replenishing Vitamin D will improve bone health in primary hyperparathyroidism, and if so, to assess the impact of the rate of vitamin D repletion.

Inclusion Criteria:

• Diagnosed PHPT, defined by an elevated serum calcium level (we will not study normocalcemic PHPT) with elevated or inappropriately normal PTH levels.
• Vitamin D3 less than 30 ng/ml

Exclusion Criteria:

• Patients with familial hyperparathyroid syndromes
• Current or past use of the following medications: bisphosphonate within past 2 years, use of lithium or thiazide diuretics, current use of cinacalcet, use of aluminum containing medications, cimetidine, colestipol, or orlistat
• Malignancy, except cured basal or squamous cell skin carcinoma or other cured cancers that are at least five years free from recurrence
• History or current diagnosis of certain medical diseases (including sarcoidosis, active infectious granulomatous disease, HIV/AIDS, chronic kidney disease (serum creatinine > 1.5 mg/dL), liver disease; GI diseases known to affect calcium metabolism; secondary hyperparathyroidism);
• We will also exclude patients with calcium above 11.5 mg/dL, urine calcium above 350 mg/day, and active nephrolithiasis because vitamin D repletion could potentially exacerbate hypercalcemia or hypercalciuria
• Other exclusions include protected individuals (institutionalized), prisoners, and any other prospective participant who might not be able to give voluntary informed consent.

6 months

Definitions do not differ from those of the ClinicalTrials.gov definitions.

Study enrollment did not reach the required number of subjects; the analysis results would not have been reliable or have enough statistical power. Therefore, samples were not processed and data was not analyzed.

Patient, investigator and study team will be blinded to study arm ramdomization.