In a recent study by researchers from the Francis Crick Institute, the National Cancer Institute (NCI) of the U.S. National Institutes of Health (NIH), and Aalborg University in Denmark, have discovered that vitamin D plays a crucial role in enhancing immunity to cancer by promoting the growth of specific gut bacteria in mice.

Published in Science, the study revealed that mice fed a diet rich in vitamin D displayed improved resistance to experimentally transplanted cancers and showed enhanced responses to immunotherapy treatment. This effect was further validated when a protein responsible for binding vitamin D in the blood was removed through gene editing, suggesting a direct correlation between vitamin D availability and cancer immunity.

Interestingly, the researchers found that vitamin D exerts its influence on epithelial cells in the intestine, leading to an increase in the abundance of a bacteria known as Bacteroides fragilis. This particular microbe was associated with heightened immunity to cancer, resulting in inhibited tumour growth. However, the precise mechanism underlying this interaction remains unclear.

To investigate the role of Bacteroides fragilis independently, mice on a normal diet were supplemented with this bacteria. These mice also displayed improved resistance to tumour growth, albeit not when subjected to a vitamin D-deficient diet.

Previous studies have hinted at a potential link between vitamin D deficiency and increased cancer risk in humans, although conclusive evidence has been lacking. To address this, the researchers analysed data from 1.5 million individuals in Denmark, revealing a correlation between lower vitamin D levels and a higher incidence of cancer. Additionally, an analysis of cancer patients suggested that those with higher vitamin D levels were more likely to respond favourably to immune-based cancer treatments.

While Bacteroides fragilis is present in the human microbiome, further research is needed to determine whether vitamin D exerts similar effects on cancer immunity in humans through the modulation of gut bacteria.

Commenting on the findings, Caetano Reis e Sousa, head of the Immunobiology Laboratory at the Crick, emphasised the significance of the discovery, stating, "What we've shown here came as a surprise: vitamin D can regulate the gut microbiome to favour a type of bacteria that gives mice better immunity to cancer."

Evangelos Giampazolias, Group Leader of the Cancer Immunosurveillance Group at the Cancer Research UK Manchester Institute, highlighted the importance of understanding how vitamin D influences the gut microbiome, offering potential avenues for cancer prevention and treatment.

Romina Goldszmid, Stadtman Investigator in NCI’s Centre for Cancer Research, underscored the need for further research to elucidate the underlying mechanisms and develop personalised treatment strategies based on these findings.

The study was supported by various funding sources, including Cancer Research UK, the UK Medical Research Council, the Wellcome Trust, and the National Institutes of Health. Dr. Nisharnthi Duggan from Cancer Research UK emphasised the need for further research to confirm the potential link between vitamin D and immune responses to cancer.

In light of these findings, experts recommend ensuring adequate vitamin D levels through sunlight exposure, diet, or supplements, while also practicing sun safety measures to reduce the risk of cancer