Effect of Variations in Plasma Magnesium Concentration on Resistance to Insulin-Mediated Glucose Disposal in Nondiabetic Subjects1

Eighteen nondiabetic volunteers were selected for these studies on the basis of their plasma magnesium (Mg) concentrations defined as being either high (> 0.83 mmol/L) or low (< 0.80 mmol/L). Although different in Mg concentration (0.90 +/- 0.02 vs. 0.73 +/- 0.01 mmol/L), the 2 groups were comparable in terms of age, gender distribution, body mass index, and waist to hip girth. Measurements were made of their plasma glucose and insulin concentrations in response to a 75-g oral glucose load and the steady state plasma insulin and glucose (SSPG) concentrations at the end of an 180-min infusion of octreotide, insulin, and glucose. The low Mg group had significantly higher plasma glucose (P < 0.001) and insulin (P < 0.002) concentrations after the oral glucose challenge. Although the steady state plasma insulin concentrations were similar during the infusion study, the SSPG concentration was significantly (P < 0.001) greater in the low Mg group (11.9 +/- 0.9 vs. 6.6 +/- 0.9 mmol/L). Finally, when the 18 patients were analyzed together, there were significant (P < 0.05 to P < 0.01) inverse correlations between Mg concentrations and glucose (r = -0.68) and insulin (r = -0.51) areas and SSPG concentrations (r = -0.60). Thus, a low Mg concentration in nondiabetic subjects was associated with relative insulin resistance, glucose intolerance, and hyperinsulinemia.