Timing of magnesium supplementation in patients with nephrolithiasis: A randomized controlled trial

Urinary magnesium plays an important role in the prevention of calcium oxalate stone formation, but the role of magnesium supplementation has yet to be clearly defined. We examined the urinary biochemistry of patients taking magnesium supplementation with meals versus while fasting.

This was a single-institution, prospective, randomized controlled pilot study examining magnesium supplementation taken with meals versus while fasting in patients with a history of calcium oxalate stones and isolated hyperoxaluria. Patients were provided a controlled diet and randomized to take magnesium supplementation either fasting or with meals during a 7-day study period. A pre-intervention and post-intervention 24-hour urinalysis was completed for all patients.

Eight patients were enrolled with 4 patients randomized to each arm of magnesium supplementation. Those taking magnesium supplementation with meals experienced a median decrease of 17.8 mg/d in urinary oxalate, increase of 33.6 mg/d in urinary magnesium, and increase of 134.8 mg/d in urinary citrate from the pre- to the post-intervention 24-hour urinalysis. Those taking supplementation while fasting experienced an average decrease of 8.5 mg/d in urinary oxalate, increase of 21.8 mg/d in urinary magnesium, and increase of 116.6 mg/d of urinary citrate.

Patients with a prior history of calcium oxalate stone formation and isolated hyperoxaluria who took magnesium supplementation with meals were found to have a more substantial improvement in urinary parameters on 24-hour urinalysis compared to those who took magnesium supplementation while fasting. Magnesium supplementation should be taken with meals if prescribed for the prevention of recurrent calcium oxalate nephrolithiasis.