Association between magnesium intake and chronic kidney diseases and kidney stones in adults aged 50 years and older: dose-response analysis of a nationally representative population-based study.

Objective: Higher serum magnesium concentrations have been linked to reduced risk of chronic kidney diseases (CKD). However, the dose-response relationships between magnesium intake and CKD and kidney stones in the general population remain unknown. This study aimed to quantitatively assess the dose-response relationships between magnesium intake and CKD and kidney stones.

Methods: Adult participants (≥50 years) from the 2007-2018 National Health and Nutrition Examination Survey were included. Magnesium intake from diet and supplements were determined with structured dietary recalls. Patients with kidney stones were identified using a standard questionnaire. CKD was defined as estimated glomerular filtration rate <60 mL/min/1.73 m². The non-linear relationships were explored with restricted cubic splines. Stratified analyses by sex were conducted.

Results: The weighted prevalence of CKD and kidney stones was 12.16% and 13.13%, respectively. A non-linear relationship between magnesium intake and CKD (P_{for non-linearity}<0.01) and kidney stones (P_{for non-linearity}=0.02) was found. There was an initial steep decrease in odds of CKD and kidney stones with increasing intakes of magnesium, and then a platform or weaker decrease in odds of CKD and kidney stones was observed beyond 350 mg/day of magnesium intake[odds ratio (95% confidence interval) for CKD: 0.60 (0.46-0.78), 0.77 (0.61-0.98) for kidney stones]. Higher magnesium intake was inversely associated with odds of CKD in both males and females, while the inverse association between higher magnesium intake and odds of kidney stones was only statistically significant in females.

Conclusions: Higher magnesium intake was non-linearly associated with lower odds of kidney stones and CKD, and a threshold level of 350 mg/day of magnesium intake was observed in adults aged 50 years and older. These findings deserve to be confirmed by prospective cohort studies.