Magnesium Supplementation Increases Urine Magnesium and Citrate in Stone Formers With Hypomagnesuria

To compare the effects of magnesium repletion by a foods-alone approach or by magnesium supplementation on urinary magnesium and citrate excretion in patients with urine magnesium <70 mg/day.

We reviewed medical records of patients in our stone prevention practice who were advised to start a magnesium supplement (Sup), 250-500 mg/day, or increase dietary magnesium consumption. We included adults with 24-hour urine magnesium (UMg) <70 mg, those who received magnesium recommendations (corroborated by the dietitian's clinical notes), and those with a follow-up 24-hour urine collection ≤18 months. Urine results were assessed by group.

Groups [No Sup (n = 74) and Sup (n = 56)] were not different for age, gender, stone history, malabsorption, or other clinical indices. All patients raised UMg (53-69 and 47-87 mg/day for No Sup and Sup, respectively); however, the increase was significantly higher in the Sup group. Moreover, while 88% of Sup patients achieved UMg ≥70 mg/day, only 58% in the No Sup group did so. Within-group increases in urine citrate were significant only in the Sup group.

Among patients with low UMg, both higher consumption from foods and magnesium supplementation significantly increased UMg. However, those who supplemented were significantly more likely to reach or exceed UMg 70 mg/day and achieved higher mean UMg. The change in urine citrate was significant only among those in the Sup group.