OBJECTIVE—To determine whether oral magnesium supplementation (as magnesium chloride [MgCl₂] solution) improves both insulin sensitivity and metabolic control in type 2 diabetic subjects with decreased serum magnesium levels.

RESEARCH DESIGN AND METHODS—This study was a clinical randomized double-blind placebo-controlled trial. A total of 63 subjects with type 2 diabetes and decreased serum magnesium (serum magnesium levels ≤0.74 mmol/l) treated by glibenclamide received either 50 ml MgCl₂ solution (containing 50 g MgCl₂ per 1,000 ml solution) or placebo daily for 16 weeks. Chronic diarrhea, alcoholism, use of diuretic and/or calcium antagonist drugs, and reduced renal function were exclusion criteria. Homeostasis model assessment for insulin resistance (HOMA-IR) was used as the parameter of insulin sensitivity and glucose and HbA_1c as parameters of metabolic control.

RESULTS—At the end of the study, subjects who received magnesium supplementation showed significant higher serum magnesium concentration (0.74 ± 0.10 vs. 0.65 ± 0.07 mmol/l, P = 0.02) and lower HOMA-IR index (3.8 ± 1.1 vs. 5.0 ± 1.3, P = 0.005), fasting glucose levels (8.0 ± 2.4 vs. 10.3 ± 2.1 mmol/l, P = 0.01), and HbA_1c (8.0 ± 2.4 vs. 10.1 ± 3.3%, P = 0.04) than control subjects.

CONCLUSIONS—Oral supplementation with MgCl₂ solution restores serum magnesium levels, improving insulin sensitivity and metabolic control in type 2 diabetic patients with decreased serum magnesium levels.