Role of Magnesium in Vitamin D Supplementation Outcomes in Adults Living with Obesity—A Narrative Review

Individuals with overweight and obesity consistently demonstrate lower circulating concentrations of serum 25-hydroxyvitamin D (25OHD), the primary biomarker of vitamin D status. Additionally, they exhibit an attenuated response to conventional vitamin D supplementation and may require doses approximately 2–3 times higher than those recommended for individuals with normal body weight to achieve equivalent serum 25OHD concentrations. However, accumulating evidence from randomized controlled trials raises concerns regarding the safety of high-dose vitamin D supplementation, with some studies reporting increased risks of falls and fractures, as well as potential adverse effects on bone mineral density and cognitive outcomes. Magnesium is an essential cofactor in vitamin D metabolism, participating in enzymatic processes required for the hepatic and renal hydroxylation of vitamin D into its active forms. Inadequate Magnesium status may therefore influence vitamin D status and response to vitamin D treatment. Previous randomized clinical trials suggest that Magnesium supplementation, administered either alone or in combination with moderate doses of vitamin D, can effectively increase serum 25OHD concentrations, particularly among individuals with overweight or obesity. Collectively, these findings suggest that optimizing Magnesium status may improve the response to vitamin D supplementation and potentially reduce the need for high-dose vitamin D therapy in obese individuals. Physicians treating overweight or obese patients for vitamin D deficiency should consider co-supplementation with Magnesium and/or encourage intake of Magnesium-rich foods to improve vitamin D status and supplementation outcomes in this population.