There is conflicting evidence regarding the relationship between magnesium deficiency and metabolic syndrome, and a systematic assessment of the literature has not been performed. Our objective was to clarify the association between magnesium levels and metabolic syndrome by performing a meta-analysis. Based on 13 eligible studies involving 14 analyses and 5496 enrolled participants, magnesium levels were significantly lower in adults with metabolic syndrome than in controls (standardized mean difference [SMD] = -0.98, 95 % confidence interval [CI] = -1.44 to -0.52). There was marked heterogeneity when all comparisons were considered (I (2) = 98 %, p < 0.001). In the subgroup meta-analysis and meta-regression model, a significant difference in magnesium levels was noted by geographic location and study quality. Magnesium levels were lower in the experimental cases than in the controls in West Asia (SMD = -3.80, 95 % CI = -5.36, -2.23) and Latin America (SMD = -1.38, 95 % CI = -1.88, -0.87), but not in East Asia (SMD = -0.01, 95 % CI = -0.30, 0.29) or Europe/Oceania (SMD = -0.25, 95 % CI = -0.53, 0.03). Moreover, the inverse association was greater in high-quality studies (SMD = -2.52, 95 % CI = -3.72, -1.32) than in low-quality studies (SMD = -0.33, 95 % CI = -0.57, -0.08). In conclusion, although there was a high level of heterogeneity, this meta-analysis provided convincing evidence of reduced magnesium levels in adults with metabolic syndrome based on the findings of observational studies. However, the present findings should be validated by additional prospective studies or trans-regional multicenter randomized controlled trials, which generally yield higher-level evidence than case-control studies and cross-sectional studies.
Clinical trial registration number: NCT02151227 ( ClinicalTrials.gov Protocol Registration System); CRD42015017946 ( www.crd.york.ac.uk/PROSPERO ).
Keywords: Hair; Insulin resistance; Magnesium; Meta-analysis; Metabolic syndrome X; Mononuclear leukocytes; Observational study; Serum; Trace elements.