Introduction: Chronic kidney disease (CKD) is associated with high cardiovascular morbidity and mortality. Recent evidence suggests that increases in both serum and intracellular magnesium (Mg) can slow or even prevent the development of vascular calcification seen in CKD. Serum calcification propensity (T50) is a novel functional test, which is associated with all-cause mortality in CKD and measures the ability of serum to delay the formation of crystalline nanoparticles. Theoretically, increasing serum Mg should improve T50 and thereby reduce the propensity towards ectopic calcification.

Methods: We conducted a randomized placebo-controlled double-blinded clinical trial to investigate the safety of 2 different doses of oral Mg supplementation in subjects with CKD stages 3 and 4 as well as their effects on intracellular Mg and T50. Thirty-six subjects with CKD stages 3 and 4 were randomized to one of 3 groups (placebo, elemental Mg 15 mmol/d or elemental Mg 30 mmol/d) given as slow-release Mg hydroxide and followed for 8 weeks.

Results: Thirty-four subjects completed the trial. Intracellular Mg remained stable throughout the trial despite significant increases in both serum and urine Mg. T50 increased significantly by 40 min from 256 ± 60 (mean ± SD) to 296 ± 64 minutes (95% confidence interval, 11-70, P < 0.05) in the Mg 30 mmol/d group after 8 weeks. No serious adverse events related to the study medication were reported during the study.

Discussion: Oral Mg supplementation was safe and well tolerated in CKD stages 3 and 4 and improved T50, but did not increase intracellular Mg. Further studies are needed to investigate the long-term effects of Mg supplementation in CKD stage 3 and 4 and whether improvement in calcification propensity is related to clinical endpoints.