Vitamin D boosts ‘good’ bacteria and improves immunity to cancer

Microbiome

Researchers have found that vitamin D encourages the growth of a type of gut bacteria in mice which improves immunity to cancer.

The researchers from the Francis Crick Institute, the National Cancer Institute (NCI) of the US National Institutes of Health (NIH) and Aalborg University in Denmark, found that mice given a diet rich in vitamin D had better immune resistance to experimentally transplanted cancers and improved responses to immunotherapy treatment.

The team found that vitamin D acts on epithelial cells in the intestine, which in turn increase the amount of a bacteria called Bacteroides fragilis.

This microbe gave mice better immunity to cancer as the transplanted tumours didn’t grow as much, but the researchers are not yet sure how.

To test if the bacteria alone could give better cancer immunity, mice on a normal diet were given Bacteroides fragilis. These mice were also better able to resist tumour growth but not when the mice were placed on a vitamin D-deficient diet.

Caetano Reis e Sousa, Head of the Immunobiology Laboratory at the Crick, and senior author, said: “What we’ve shown here came as a surprise – vitamin D can regulate the gut microbiome to favour a type of bacteria which gives mice better immunity to cancer.

“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.”

Similar findings in May 2023 showed that patients with advanced skin cancer responded better to treatment with immune checkpoint inhibitors when they maintained normal vitamin D levels.

The role of vitamin D in the microbiome

Previous studies have proposed a link between vitamin D deficiency and cancer risk in humans, although the evidence hasn’t been conclusive.

To investigate this, the researchers analysed a dataset from 1.5 million people in Denmark, which highlighted a link between lower vitamin D levels and a higher risk of cancer. A separate analysis of a cancer patient population also suggested that people with higher vitamin D levels were more likely to respond well to immune-based cancer treatments.

Although Bacteroides fragilis is also found in the microbiome in humans, more research is needed to understand whether vitamin D helps provide some immune resistance to cancer through the same mechanism.

Evangelos Giampazolias, former postdoctoral researcher at the Crick, and now Group Leader of the Cancer Immunosurveillance Group at the Cancer Research UK Manchester Institute, said: “Pinpointing the factors that distinguish a ‘good’ from a ‘bad’ microbiome is a major challenge. We found that vitamin D helps gut bacteria to elicit cancer immunity improving the response to immunotherapy in mice.

“A key question we are currently trying to answer is how exactly vitamin D supports a ‘good’ microbiome. If we can answer this, we might uncover new ways in which the microbiome influences the immune system, potentially offering exciting possibilities in preventing or treating cancer.”

Diana Spencer, Senior Digital Content Editor, DDW

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