Magnesium Supplementation Does Not Affect Blood Calcium Level in Treated Hypoparathyroid Patients

Abstract

Context: Magnesium is involved in the homeostasis of calcium metabolism, and magnesium deficiency may lead to clinically significant hypocalcemia. We have had two cases in our department in which treated hypoparathyroid patients with stable calcium levels developed hypercalcemia in conjunction with supplementary magnesium use. To our knowledge, there has been no prospective study looking at the effect of supplementary magnesium on calcium homeostasis in hypoparathyroid patients. Objective: The aim of this pilot study was to evaluate whether magnesium treatment affects plasma calcium levels in hypoparathyroid patients. Design and Setting: We conducted a prospective, two-phase, uncontrolled treatment trial at a referral center of endocrine disorders. Participants: We enrolled treated (calcium + vitamin D analog) hypoparathyroid patients with normal plasma magnesium levels. Intervention: Three weeks of treatment with oral magnesium (350 mg/d) were followed by 2 wk off treatment. Measures: We compared the plasma ionized calcium level after 3 wk of treatment to the pretreatment value. Plasma calcium, phosphate, magnesium, and creatinine levels were measured before treatment, after 3 wk on magnesium, and 2 wk after stopping magnesium treatment. Results: Ten patients completed the trial. Supplementary treatment with magnesium for 3 wk did not change calcium levels in these patients. Magnesium supplementation induced a small but statistically significant increase in the plasma magnesium level, but levels of phosphate and creatinine remained stable. Conclusions: Magnesium supplementation did not influence plasma calcium levels in treated hypoparathyroid patients.