Gut bacteria , gut flora, microbiome. Bacteria inside the small intestine, concept, representation. 3D illustration.
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Researchers at the Francis Crick Institute, the National Cancer Institute (NCI) of the U.S. National Institutes of Health, and Aalborg University in Denmark have discovered that vitamin D can increase the amount of a certain type of gut bacteria, providing better immunity to cancer. 

Vitamin D is essential for human health and can be acquired through sun exposure, foods, and supplements. It promotes bone growth, reduces inflammation, and is important for cell growth, glucose metabolism, the immune system, and neuromuscular functions. Previous studies have shown that it can reduce the risk of cancer and promote the growth of beneficial gut bacteria

In this most recent study, published in the journal Science, the researchers found that mice, who had been given a vitamin D-rich diet showed better resistance to transplanted cancers, than those on a deficient diet. 

The research team discovered that vitamin D affects epithelial cells in the intestine, resulting in the increased growth of Bacteroides fragilis, a type of gut bacteria. Hence, mice on a vitamin D-rich diet were better able to resist the growth of tumors and showed improved responses to treatment with immune checkpoint inhibitors, a type of cancer immunotherapy. 

“What we’ve shown here came as a surprise—vitamin D can regulate the gut microbiome to favor a type of bacteria which gives mice better immunity to cancer,” said Caetano Reis e Sousa, head of the immunobiology laboratory at the Crick, and senior author, in a press release.

“This could one day be important for cancer treatment in humans, but we don’t know how and why vitamin D has this effect via the microbiome. More work is needed before we can conclusively say that correcting a vitamin D deficiency has benefits for cancer prevention or treatment.”

To investigate the link between vitamin D deficiency and increased cancer risk in humans— as shown by previous studies—the researchers also analyzed a dataset comprising 1.5 million people in Denmark. They found that there was indeed a link between lower vitamin D levels and a higher cancer risk. 

In another analysis of a cancer patient population, the researchers observed that people with higher vitamin D levels in their blood had a greater chance of responding well to cancer immunotherapies. 

“Our findings indicate a previously unappreciated connection between vitamin D, microbial commensal communities, and immune responses to cancer. Collectively, they highlight vitamin D levels as a potential determinant of cancer immunity and immunotherapy success,” wrote the authors.

“These findings contribute to the growing body of knowledge on the role of microbiota in cancer immunity and the potential of dietary interventions to fine-tune this relationship for improved patient outcomes,” added Romina Goldszmid, Stadtman Investigator in NCI’s Center For Cancer Research. “However, further research is warranted to fully understand the underlying mechanisms and how they can be harnessed to develop personalized treatment strategies.”

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