Aims The aim of this study was to assess the evidence on the effect of oral magnesium supplementation on glycaemic control in patients with Type 2 diabetes.
Methods We searched the electronic databases of medline, embase and the Cochrane Controlled Trials Register up to January 2005. We identified nine randomized double-blind controlled trials with a total of 370 patients with Type 2 diabetes and of duration 4–16 weeks. The median dose of oral magnesium supplementation was 15 mmol/day (360 mg/day) in the treatment groups. The primary outcome was glycaemic control, as measured by glycated haemoglobin (HbA1c) or fasting blood glucose levels; the secondary outcomes included body mass index, blood pressure (BP) and lipids. Using a random-effects model, we calculated the weighted mean differences (WMD) and 95% confidence interval (CI).
Results After a median duration of 12 weeks, the weighted mean post-intervention fasting glucose was significantly lower in the treatment groups compared with the placebo groups [−0.56 mmol/l (95% CI, −1.10 to −0.01); P for heterogeneity = 0.02]. The difference in post-intervention HbA1c between magnesium supplementation groups and control groups was not significant [−0.31% (95% CI, −0.81 to 0.19); P for heterogeneity = 0.10]. Neither systolic nor diastolic BP was significantly changed. Magnesium supplementation increased on high-density lipoprotein (HDL) cholesterol levels [0.08 mmol/l (95% CI, 0.03 to 0.14); P for heterogeneity = 0.36] but had no effect on total cholesterol, low-density lipoprotein (LDL) cholesterol and triglyceride.
Conclusions Oral magnesium supplementation for 4–16 weeks may be effective in reducing plasma fasting glucose levels and raising HDL cholesterol in patients with Type 2 diabetes, although the long-term benefits and safety of magnesium treatment on glycaemic control remain to be determined.