The effect of oral magnesium supplementation on glycemic control and metabolic parameters in type 2 diabetes mellitus: a double-blind randomized controlled trial

Background This randomized controlled trial (RCT) assessed the effect of oral magnesium (Mg) supplementation on glycated hemoglobin (HbA1c) and metabolic biomarkers in adults with Type 2 Diabetes Mellitus (T2DM). Methods This was a prospective, randomized, double-blind, placebo-controlled, parallel-group clinical trial with intention-to-treat (ITT) and per-protocol (PP) analyses. Adults (≥18 years) with T2DM were randomized 1:1 to receive magnesium oxide (500 mg; 302 mg elemental) or placebo. Eligibility criteria included a glycated hemoglobin (HbA1c) level ≥7.0% and a creatinine clearance >30 mL/min. Simple randomization was performed using a sealed-envelope method. Biochemical and clinical parameters were assessed at baseline and at three follow-up visits over 12 months. Results A total of 247 participants were included in the ITT analysis (Mg-oxide, n=118; placebo, n=129). Median age was 58 (50–65) years, and median diabetes duration was 16 (10–22) years. Hypomagnesemia was present in 7.3% by ionized magnesium (iMg) and 8.1% by total magnesium (tMg). Mg-oxide supplementation significantly reduced fasting blood glucose in a subgroup of the cohort (FBG; p = 0.039) and resulted in a modest, non-significant reduction in HbA1c (−0.30% vs. −0.05%; p = 0.145), with a higher proportion achieving goal attainment/controlled HbA1c (<7%) compared with placebo (14.0% vs. 6.0%; p = 0.043). HbA1c reductions were more pronounced among participants with baseline hypomagnesemia (−0.60% vs. +0.25%; p = 0.074), or diabetes duration ≤15 years (−0.40% vs. 0.00%; p = 0.085). No differences were observed in other metabolic parameters, clinical outcomes or adverse drug reactions between groups. Conclusions Although median HbA1c reduction did not reach statistical significance, Mg-oxide supplementation improved Mg status and showed favorable trends in glycemic control without compromising safety. These findings support Mg supplementation as a safe adjunct to long-term T2DM management, particularly among selected subgroups, given the study’s limitations. Clinical Ttrial Registration https://clinicaltrials.gov/ , identifier NCTO5774015.