Serum Magnesium Concentrations in the United States—An Updated Population Reference Interval in Children and Adults

BACKGROUND: Serum magnesium is a practical biomarker for assessing nutritional status in clinical settings, yet reference intervals commonly used in the United States largely reflect data from NHANES I (1971-1974). OBJECTIVES: The aim of this study is to describe serum magnesium concentrations across the US population and establish contemporary population-based reference intervals for children and adults. METHODS: This cross-sectional study used data from nonpregnant and nonlactating civilian participants in the 2021-2023 NHANES data cycles. Reference intervals were estimated following the International Federation of Clinical Chemistry recommendations. Primary analyses categorized children (aged 12-18 y) by sex and adults (aged ≥19 y) by sex, age, and metabolic health status [total population, metabolically healthy, hypertension, diabetes, and chronic kidney disease (CKD)]. Linear regression models were used to compare subgroups, and sensitivity analyses were conducted to assess robustness of primary findings. RESULTS: The final analytic sample included 787 children and 5474 adults. Girls had significantly lower mean serum magnesium than boys (P = 0.003), although differences were small. The reference interval was 1.70-2.19 mg/dL (0.70-0.90 mmol/L; 1.40-1.80 mEq/L) for boys and 1.64-2.18 mg/dL (0.68-0.90 mmol/L; 1.35-1.79 mEq/L) for girls based on data from the total population. Mean serum magnesium concentrations were significantly lower in adult males and females with diabetes (P < 0.001; P < 0.001), hypertension (P = 0.012; P = 0.029), or CKD (P = 0.007; P = 0.002) compared with those who were metabolically healthy, respectively, and in females compared with males (P < 0.001). The reference interval was 1.72-2.26 mg/dL (0.71-0.93 mmol/L; 1.42-1.86 mEq/L) for males and 1.70-2.21 mg/dL (0.70-0.91 mmol/L; 1.40-1.82 mEq/L) for females based on data from the metabolically healthy population. Estimated prevalence of chronic latent magnesium deficiency (CLMD), represented by a serum magnesium concentration <2.06 mg/dL (0.85 mmol/L; 1.70 mEq/L), was 67.8% in adults. CONCLUSIONS: This study provides contemporary population-based reference intervals for serum magnesium for children and adults and suggests that a substantial portion of the US population is at risk of CLMD.