U-shaped association of serum magnesium with mild cognitive impairment among hemodialysis patients: a multicenter study

Background The optimal serum magnesium level of patients undergoing hemodialysis (HD) with cognitive impairment is still unclear. This study aimed to evaluate the association between serum magnesium levels and mild cognitive impairment among HD patients. Methods This was a multicenter observational study. Patients undergoing hemodialysis from 22 dialysis centers in Guizhou Province, China were recruited into the study. HD patients were divided into five groups according to serum magnesium quintile. Cognitive function was measured with Mini Mental State Examination. The outcome was an incident mild cognitive impairment (MCI). Multivariate logistic regression analysis, restricted cubic spline and subgroup analysis were applied to explore the association of serum magnesium level with MCI. Results Among 3562 HD patients (mean age 54.3 years, 60.1% male), the prevalence of MCI was 27.2%. After adjusting for confounders, serum magnesium 0.41-0.83 mmol/L [odds ratios (OR) 1.55, 95% confidence interval (CI): 1.10-2.18] had a higher risk of MCI compared with serum magnesium of 1.19-1.45 mmol/L. A U-shaped association was identified between the serum magnesium and incident MCI (P for non-linearity = 0.004). The optimal range of magnesium level with the lowest risk of MCI was 1.12-1.24 mmol/L. As the serum magnesium level was lower than 1.12 mmol/L, the risk of MCI decreased by 24% per standard deviation (SD) increase in serum magnesium (OR 0.76, 95%CI: 0.62-0.93); when the serum magnesium level exceeds 1.24 mmol/L, a rise per SD increased the risk of MCI by 21% (OR = 1.20, 95%CI: 1.02-1.43). Subgroup analyses demonstrated that the associations were robust among individuals with low educational level, smoking, living alone, no working, and without hypertension or diabetes. Conclusions Serum magnesium has a U-shaped association with MCI among HD patients. Both lower and higher serum magnesium can increase the risk of MCI for this population specifically. The optimal serum magnesium range with the lowest risk of MCI was 1.12-1.24 mmol/L.