This study evaluated the efficacy of oral magnesium supplementation in the reduction of plasma glucose levels in adults with prediabetes and hypomagnesaemia.

A total of 116 men and non-pregnant women, aged 30 to 65years with hypomagnesaemia and newly diagnosed with prediabetes, were enrolled into a randomized double-blind placebo-controlled trial to receive either 30mL of MgCl₂ 5% solution (equivalent to 382mg of magnesium) or an inert placebo solution once daily for four months. The primary trial endpoint was the efficacy of magnesium supplementation in reducing plasma glucose levels.

At baseline, there were no significant statistical differences in terms of anthropometric and biochemical variables between individuals in the supplement and placebo groups. At the end of follow-up, fasting (86.9±7.9 and 98.3±4.6mg/dL, respectively; P=0.004) and post-load glucose (124.7±33.4 and 136.7±23.9mg/dL, respectively; P=0.03) levels, HOMA-IR indices (2.85±1.0 and 4.1±2.7, respectively; P=0.04) and triglycerides (166.4±90.6 and 227.0±89.7, respectively; P=0.009) were significantly decreased, whereas HDL cholesterol (45.6±10.9 and 46.8±9.2mg/dL, respectively; P=0.04) and serum magnesium (1.96±0.27 and 1.60±0.26mg/dL, respectively; P=0.005) levels were significantly increased in those taking MgCl₂ compared with the controls. A total of 34 (29.4%) people improved their glucose status (50.8% and 7.0% in the magnesium and placebo groups, respectively; P<0.0005).

Our results show that magnesium supplementation reduces plasma glucose levels, and improves the glycaemic status of adults with prediabetes and hypomagnesaemia.