No beneficial effects of vitamin D supplementation on muscle function or quality of life in primary hyperparathyroidism: results from a randomized controlled trial

Context: Impairments of muscle function and strength in patients with primary hyperparathyroidism (PHPT) are rarely addressed, although decreased muscle function may contribute to increased fracture risk. Objective: We aimed to assess the changes in muscle strength, muscle function, postural stability, quality of life (QoL), and well-being during treatment with vitamin D or placebo before and after parathyroidectomy (PTX) in PHPT patients. Design: A randomized placebo-controlled trial. Patients: We included 46 PHPT patients, mean age 58 (range 29-77) years and 35 (76%) were women. Interventions: Daily treatment with 70 mu g (2800 IU) cholecalciferol or placebo for 52 weeks. Treatment was administered 26 weeks before PTX and continued for 26 weeks after PTX. Main outcome measures: Changes in QoL and measures of muscle strength and function. Results: Preoperatively, 25-hydroxyvitamin D (25OHD) increased significantly (50-94 nmol/l) compared with placebo (57-52 nmol/l). We did not measure any beneficial effects of supplementation with vitamin D compared with placebo regarding well-being, QoL, postural stability, muscle strength, or function. In all patients, we measured marked improvements in QoL, well-being (P< 0.01), muscle strength in the knee flexion and extension (P< 0.001), and muscle function tests (P< 0.01) after surgical cure. Postural stability improved during standing with eyes closed (P< 0.05), but decreased with eyes open (P< 0.05). Conclusions: Patients with PHPT and 25OHD levels around 50 nmol/l did not benefit from vitamin D supplementation concerning muscle strength, muscle function, postural stability, well-being, or QoL. Independent of preoperative 25OHD levels, PTX improved these parameters.