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Vitamin D Boosts Gut Bacteria and Enhances Cancer Immunity in Mice

Vitamin D capsules on a blue background.
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Vitamin D shows protective effects against cancer in a new study from the Francis Crick Institute, the National Cancer Institute (NCI) of the US National Institutes of Health (NIH) and Aalborg University in Denmark.


Published in Science, the study found the vitamin promotes the growth of a type of gut bacteria, which enhances resistance to cancer in mice.

Vitamin D and the immune system

Vitamin D is a fat-soluble vitamin, essential for maintaining healthy bones and regulating various physiological processes in the body.

Vitamin D plays a crucial role in immune modulation, regulating the expression of genes involved in the immune response and enhancing the function of immune cells. It also contributes to immune function by shaping the gut microbiome, influencing the composition and diversity of gut bacteria.


In cancer, data suggests vitamin D is capable of inhibiting cancer cell growth, induce apoptosis and suppress angiogenesis.

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 “We know that vitamin D deficiency can cause health problems, however, there isn't enough evidence to link vitamin D levels to cancer risk,” said Dr. Nisharnthi Duggan, research information manager at Cancer Research UK.


In the study, mice were administered either a standard diet or a diet rich in vitamin D. Their immune responses to experimentally transplanted cancer were observed, as well as their reaction to immunotherapy treatment.

Mice that received a high vitamin D diet had better immune resistance to the cancer and an improved response to the immunotherapy treatment, compared to the controls. The same result was also observed in genetically-edited mice that lack the protein that binds to vitamin D in the blood and keeps it away from tissues.

Vitamin D acted on the epithelial cells in the intestine, resulting in a higher abundance of gut bacteria Bacteroides fragilis (B. fragilis). The growth of the bacteria increased the mice immune response to cancer, suppressing tumor growth, although the researchers have yet to determine the underlying mechanism of this finding.


Mice on the standard diet were supplemented with B. fragilis to test whether the bacteria alone triggers cancer-resistant effects. Tumor growth suppression was also observed in this group, however the same effects were not seen when the mice were placed on a vitamin D deficient diet.

Investigating vitamin D’s effects in humans

To investigate the effects of B. fragilis and vitamin D in humans, the researchers analyzed data from 1.5 million people in Denmark. They found that decreased levels of vitamin D are associated with a higher risk of cancer. A second analysis looked at a cancer patient population and found those with higher vitamin D levels were more likely to have a positive response to immune-based cancer treatments.


Although B. fragilis are found in humans, further research is needed to show whether the cancer-resistant effects also work through the same mechanism.

Vitamin D as a potential treatment option

“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,” said Dr. Romina Goldszmid, author and Stadtman Investigator at the NCI’s Center For Cancer Research.


“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,” said Dr. Caetano Reis e Sousa, senior author and head of the Immunobiology Laboratory at the Francis Crick Institute.


Reference: Giampazolias E, Costa MP da, Lam KC, et al. Vitamin D regulates microbiome-dependent cancer immunity. Science. 2024. doi: 10.1126/science.adh7954

This article is a rework of a press release issued by the Francis Crick Institute. Material has been edited for length and content.