Magnesium status of patients with renal stones and its effect on urinary citrate excretion

To assess the magnesium status and its effect on urinary citrate excretion in patients with renal stones, as they have a low muscular magnesium content.

Using a magnesium-tolerance test (0.1 mmol/L MgSO4/kg body weight, delivered intravenously), the magnesium status was assessed in 17 patients with renal stones from rural North-east Thailand, and in three groups of normal subjects from different environments (i.e. 17 from rural Central Thailand, 16 from urban and 14 from rural North-east Thailand). Participants with magnesium deficiency (magnesium retention > 50%) were supplemented with 300 mg chelated magnesium daily for 1 month and reassessed. Their urinary citrate excretion was also measured before and after supplementation.

Nine of the patients with renal stones were magnesium deficient, as were six normal subjects from the same area, whereas only one and two of the rural Central and urban North-east Thais had magnesium deficiency. The magnesium status of the 13 deficient subjects significantly improved (P = 0.003) after supplementation with chelated magnesium. The supplement also caused a significant increase in mean (sd) urinary citrate excretion, from 237.7 (173.1) to 361.3 (284.1) mg/day (P= 0.012).

These results indicate that magnesium deficiency is common among patients with renal stones in rural North-east Thailand, and that the probable cause is environmental. The increase in urinary citrate excretion after magnesium supplementation suggests that magnesium is important in renal stone formation, through its effect on citrate metabolism.