Endocrinology · Medical Literature
The effect of oral magnesium supplementation on glycemic control and metabolic parameters in type 2 diabetes mellitus: a double-blind randomized controlled trial.
Abstract
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). 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. 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. 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. https://clinicaltrials.gov/, identifier NCTO5774015.
Clinical relevance
Hypomagnesemia is prevalent in T2DM and may impair insulin signaling, yet oral magnesium supplementation remains underutilized as an adjunct in glycemic management. This 12-month double-blind RCT addresses the gap in long-term, placebo-controlled evidence for magnesium oxide supplementation in adults with established T2DM (median disease duration 16 years) and suboptimal glycemic control (HbA1c ≥7.0%). Clinicians managing refractory or long-standing T2DM should be aware of this data given the low risk profile of supplementation and the potential for benefit in select subgroups.
Key findings
1. HbA1c reduction was greater in the magnesium oxide group versus placebo (-0.30% vs. -0.05%), but this difference did not reach statistical significance (p = 0.145) in the ITT population of 247 participants. 2. A significantly higher proportion of participants in the magnesium oxide group achieved glycemic goal attainment (HbA1c <7.0%) compared with placebo (14.0% vs. 6.0%; p = 0.043). 3. Magnesium oxide supplementation produced a statistically significant reduction in fasting blood glucose (FBG) in a pre-specified subgroup of the cohort (p = 0.039), though full subgroup details were not elaborated in the abstract. 4. Among participants with baseline hypomagnesemia, HbA1c reduction was more pronounced in the magnesium oxide group versus placebo (-0.60% vs. +0.25%; p = 0.074), suggesting a clinically meaningful though statistically trend-level benefit in this subgroup. 5. Participants with diabetes duration ≤15 years showed a greater HbA1c reduction trend with magnesium oxide versus placebo (-0.40% vs. 0.00%; p = 0.085), indicating disease duration as a potential effect modifier. 6. Hypomagnesemia prevalence was relatively low at baseline (7.3% by ionized magnesium; 8.1% by total magnesium), and no differences in other metabolic parameters, clinical outcomes, or adverse drug reactions were observed between groups.
Practice implications
Magnesium oxide 500 mg daily (302 mg elemental magnesium) may be considered as a safe, low-risk adjunct to standard T2DM pharmacotherapy, particularly in patients with documented hypomagnesemia or shorter diabetes duration (≤15 years), where glycemic benefit trends were most pronounced. Clinicians should assess baseline magnesium status (both ionized and total magnesium) in patients with suboptimal HbA1c, as this may identify a subgroup most likely to respond to supplementation. Given the absence of significant adverse drug reactions over 12 months and the eligibility criterion of creatinine clearance >30 mL/min, this supplementation strategy appears safe across a broad T2DM population, though efficacy evidence remains strongest for selected subgroups and larger confirmatory trials are warranted.