In a meta-analysis of eighteen randomized controlled trials, reviewers assessed the effect of magnesium supplementation versus placebo in patients diagnosed with diabetes or those identified as being at high risk for diabetes. Compared to placebo, magnesium supplementation reduced blood sugar levels in diabetics. Similarly, in people who had not yet developed diabetes but who were at higher risk for it, magnesium supplementation lowered blood sugar levels following a glucose challenge. They also tended to trend toward lower markers for insulin resistance, leading authors to conclude that “magnesium supplementation appears to have a beneficial role” in markers of glucose metabolism.
For additional reading, refer to the abstract, Effect of magnesium supplementation on glucose metabolism in people with or at risk of diabetes: a systematic review and meta-analysis of double-blind randomized controlled trials published in the December 2016 issue of European Journal of Clinical Nutrition.