Vitamin D may decrease PTH without increasing blood, urinary calcium

High-dose daily vitamin D supplementation appears to safely decrease parathyroid hormone in patients with primary hyperparathyroidism without an accompanying increase in blood or urinary calcium, results from a recent study have found.

“Daily supplementation with a high vitamin D dose safely improved vitamin D status and decreases [parathyroid hormone] in primary hyperthyroid patients without increasing plasma or urinary calcium,” the researchers wrote. “The vitamin D treatment is accompanied by reduced bone resorption and improved bone mineral density before operation. This study supports a wider use of vitamin D supplementation in primary hyperthyroid patients.”

The randomized, double blind, placebo-controlled, parallel group trial recruited 46 patients from the outpatient clinic of the department of endocrinology and internal medicine, Aarhus University Hospital, Denmark. All enrolled patients were aged at least 18 years, with known hyperparathyroid hypercalcemia on a minimum of two occasions and vitamin D deficiency. Vitamin D insufficiency was defined as 25-hydroxyvitamin D levels <80 nmol/L.

Patients included in the study also needed to be eligible for parathyroidectomy. The researchers collected baseline information about the study participants’ medical history, socioeconomic factors and diet, including their intake of several fish, fruit, milk and milk products, as well as vitamin supplement usage.

Participants were randomly assigned to a daily regimen of 70 mcg (2,800 IU) oral cholecalciferol (vitamin D3) or placebo for 1 year. Six months after the start of the study, patients underwent parathyroidectomy surgery, and they remained on their assigned regimens for 6 months after surgery.

The primary endpoint of the study was preoperative changes in preoperative parathyroid hormone (PTH) levels, with secondary endpoints including safety markers and measures of calcium stability and bone metabolism. The researchers found that serum 25-(OH)D levels increased from 50 nmol/L to 94 nmol/L in the experimental group and decreased from 57 nmol/L to 52 nmol/L in the placebo group (P<.001). Preoperative PTH levels were significantly decreased (17%) in the vitamin D group vs. the placebo group (P=.01). Lumbar spine BMD was increased by 2.5% in the vitamin D group (P=.01), and the resorptive bone marker showed a 22% decrease (P<.005). Although trabecular bone score did not respond to vitamin D treatment, it improved after surgery. The postoperative PTH levels continued to be decreased in the treatment group compared with the placebo group (P=.04). No difference in blood calcium or creatine was noted between the groups.

Disclosure: The researchers report no relevant financial disclosures.