A recent study from the Vanderbilt-Ingram Cancer Center has unveiled significant findings regarding the relationship between magnesium and vitamin D levels in the body. Conducted as a randomized clinical trial, the research indicates that magnesium may be vital for maintaining optimal vitamin D levels, particularly for those who are deficient. The results suggest that magnesium not only boosts vitamin D in individuals with low levels but also helps regulate it in those with excessive amounts.
The study, published in the December 2025 issue of The American Journal of Clinical Nutrition, challenges previous assumptions about vitamin D supplementation. Often touted for its health benefits, vitamin D’s effectiveness has varied widely among individuals, leading to mixed results in studies linking it to diseases such as cancer and heart disease. The new findings provide clarity on these inconsistencies by highlighting magnesium’s role as a regulatory agent.
Qi Dai, MD, PhD, who is the lead author of the study and an Ingram Professor of Cancer Research, explained that the ideal vitamin D levels appear to fall within a U-shaped curve. This curve indicates that both low and high vitamin D levels could be associated with increased health risks, particularly cardiovascular disease. The research supports earlier findings from 2013 by the same team, which identified an association between low magnesium intake and low vitamin D levels.
In this recent trial, which included 250 adults identified as being at higher risk for colorectal cancer, participants were administered either magnesium supplements or a placebo. The dosages were tailored to their usual dietary intake, allowing researchers to observe the effects more accurately. Notably, magnesium did not simply elevate vitamin D levels indiscriminately; rather, it functioned as a regulator by decreasing vitamin D levels in participants who had high amounts.
Dai emphasized the significance of these findings, stating, “Magnesium deficiency shuts down the vitamin D synthesis and metabolism pathway.” The study reveals a potential pathway for understanding why vitamin D supplementation yields varied results across different individuals.
Research continues to show that vitamin D insufficiency is a prevalent public health concern in the United States, with many people advised to take supplements based on blood test results. However, Martha Shrubsole, PhD, a research professor of Medicine in the Division of Epidemiology and co-author of the study, noted that magnesium deficiency is often overlooked. Estimates suggest that up to 80 percent of the population does not consume adequate magnesium to meet the recommended dietary allowance (RDA).
Shrubsole stated, “Vitamin D insufficiency is something that has been recognized as a potential health problem on a fairly large scale in the U.S.” She further pointed out that while many individuals receive recommendations for vitamin D supplements, the role of magnesium in optimizing vitamin D levels is crucial and warrants further investigation.
To address magnesium needs, the researchers advocate for dietary sources over supplementation. Foods rich in magnesium include dark leafy greens, beans, whole grains, dark chocolate, fatty fish like salmon, nuts, and avocados. By focusing on dietary intake, individuals can potentially enhance their magnesium levels in a more balanced manner.
As research continues, the team at Vanderbilt will further explore the implications of magnesium on vitamin D levels as part of the ongoing Personalized Prevention of Colorectal Cancer Trial. Their work aims to resolve the ongoing debates regarding the relationship between vitamin D and health risks, particularly in light of previous conflicting findings from major studies, including the VITAL trial.
This new study underscores the importance of understanding the interplay between minerals and vitamins in promoting overall health, paving the way for more tailored approaches to supplementation and dietary recommendations.