High serum levels of magnesium increase the risks for cardiovascular (CV) events and death in patients with chronic kidney disease (CKD), suggesting clinicians need to be cautious about prescribing magnesium supplementation in these patients, investigators reported.

In a retrospective observational study, investigators led by Isabel Galán, MD, of Hospital general Universitario Reina Sofia, Murcia, Spain, found that serum magnesium levels increased as kidney function decreased, according to study findings published in the Journal of Renal Nutrition. In adjusted analyses, patients with hypermagnesemia, defined as serum magnesium levels higher than 2.2 mg/dL, had significant 34% and 54% increased risks for CV events and all-cause mortality, respectively, compared with those who had serum magnesium levels in the normal range (1.7 to 2.18 mg/dL). Hypermagnesemia remained significantly associated with increased all-cause mortality in a propensity score analysis that compared 287 patients with hypermagnesemia and 287 without it. The study found no significant associations between hypomagnesemia (less than 1.69 mg/dL) and either CV events or all-cause mortality.

“In the past decade, recommendations to supplement dietary magnesium intake to patients with chronic kidney disease have appeared in the literature,” Dr Galán and colleagues wrote. “Our study suggests that these recommendations should be applied cautiously, if at all.”

The study included 746 patients with CKD who had a mean age of 70 years at baseline. Of these, 45.2% had stage 3 CKD and 35.9% had stage 4 CKD. The cohort had a mean serum magnesium level of 2.09 mg/dL at baseline. During a mean follow-up period of 42.6 months, 341 patients (45.7%) experienced either a cardiovascular event, initiation of kidney replacement therapy (KRT), or death. A total of 104 patients (19.6%) died, with CV events identified as the cause of death for 68 patients (65.1%).


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In addition, 221 patients (29.6%) had a fatal or nonfatal CV event: 75 (33.9%) had ischemic heart disease, 29 (11.8%) had a stroke, 25 (11.3%) were diagnosed with peripheral vascular disease, and 95 (42.9%) had congestive heart failure.

KRT was initiated in 145 patients (19.4%), but the study found no association between serum magnesium levels and KRT initiation.

With respect to associations between medication use and serum magnesium levels, Dr Galán and colleagues found that only calcitriol therapy was significantly associated with higher serum magnesium levels, whereas treatment with calcium supplements and proton pump inhibitors were significantly associated with lower serum magnesium levels.

Study limitations included its observational design the use of only a single baseline measurement of serum magnesium, Dr Galán’s team noted. The main strength of the study was its inclusion of the largest cohort to date of patients with stage and 4 CKD that examined serum magnesium levels and their consequences, according to the authors. Another strength was the use of propensity score matching “to overcome some of the limitations that are inherent to any observational study.”

Reference

Galán I, Vega A, Goicoechea M, et al. Impact of serum magnesium levels on kidney and cardiovascular prognosis and mortality in CKD patients. Published online December 9, 2020. J Ren Nutr. doi: 10.1053/j.jrn.2020.09.004