A new clinical study has found that taking magnesium may promote the growth of gut bacteria that help prevent the development of colon cancer. However, this effect is not observed in everyone and depends on individual genetic characteristics and sex.

Colorectal Cancer: The Scope of the Problem

Despite the widespread use of colonoscopy, which has reduced the incidence of colorectal cancer, it remains the third most common cancer worldwide and the second leading cause of cancer-related deaths.

The Impact of Magnesium on the Gut Microbiome

Research conducted by the Vanderbilt University Medical Center (VUMC) showed that magnesium supplements increase the number of gut bacteria capable of suppressing the growth of colorectal cancer. Previous studies established that magnesium helps raise blood vitamin D levels in cases of deficiency. The new data indicate that magnesium also boosts the number of microbes that can synthesize vitamin D in the gut without sunlight and locally inhibit tumor development.

Sunlight is the main source of vitamin D, which is essential for strong bones and overall health. A deficiency in this vitamin is linked to an increased risk of colorectal cancer.

Study Design

The double-blind, randomized, controlled trial involved 240 people with a history of colorectal polyps—a known risk factor for colon cancer. Participants were randomly assigned to two groups: one received individually selected magnesium supplements (magnesium glycinate), and the other received a placebo. The dosage was determined based on the dietary calcium-to-magnesium ratio, which is typically about 2:1 in favor of calcium. The intervention lasted 12 weeks.

Researchers collected stool samples, rectal swabs, rectal tissue biopsies, and blood before and after the intervention. Special attention was given to two types of bacteria—Carnobacterium maltaromaticum and Faecalibacterium prausnitzii—which in previous mouse studies were shown to stimulate vitamin D production and reduce cancer risk.

The study also examined the influence of genetic differences in the TRPM7 gene, which regulates magnesium levels in the body. TRPM7 can be thought of as a "magnesium gate" in cells: if it malfunctions, magnesium levels may be disrupted.

Genetic Features and Their Role

Researchers looked for a so-called "missense variant"—a small DNA mutation where one amino acid in a protein is replaced by another. In this case, they studied the Thr1482Ile variant in TRPM7, where threonine is replaced by isoleucine. Such a change can affect how well the protein functions.

Main Findings

In people without the TRPM7 missense variant (with a normal genome), magnesium intake increased the amount of C. maltaromaticum and, to a lesser extent, F. prausnitzii. This effect was most pronounced in women, possibly due to hormonal influences such as estrogen. Among participants with the Thr1482Ile variant, magnesium sometimes had the opposite effect, reducing the levels of these bacteria.

Interestingly, the increase in bacterial numbers did not explain the rise in vitamin D levels, suggesting that magnesium affects vitamin D metabolism both directly and via the microbiome, but through different mechanisms.

Link to Polyp Risk

Additional colonoscopies showed that people with the highest levels of F. prausnitzii in rectal tissue had about 2.8 times higher risk of developing new polyps compared to those with the lowest levels. This association was statistically significant. Higher levels of C. maltaromaticum were linked to about an 85% lower risk of developing serrated polyps, which are less common but associated with a higher risk of colorectal cancer and can progress to malignancy more quickly. However, this result was only "marginally significant" and requires further confirmation. No clear link between bacteria and polyp risk was found in stool samples.

Study Limitations

The study has several limitations. After adjusting for multiple comparisons, the increase in F. prausnitzii was no longer statistically significant, so the results should be interpreted with caution. It was not possible to determine which specific bacterial strains were responsible for the effect, and the impact may vary by strain. Changes in the microbiome were measured in relative terms, which can fluctuate even if the absolute number of bacteria remains unchanged. Most participants were elderly, white, and from a single region (Tennessee, USA), so the findings may not be universally applicable. Additionally, the study lasted only 12 weeks, and long-term effects are still unknown.

Perspectives and Conclusions

Nevertheless, the study suggests that magnesium supplements may help prevent colorectal cancer, especially in women and in people without certain TRPM7 genetic variants. This opens up possibilities for personalized nutrition, where genetic testing could help determine who would benefit most from magnesium supplementation. However, further research is needed before clinical recommendations can be made.