Researchers at 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 can promote the growth of a specific type of gut bacteria in mice, which in turn enhances immunity to cancer. Their findings, published in Science, show that mice fed a diet rich in vitamin D exhibited better immune resistance to transplanted cancers and improved responses to immunotherapy. This effect was observed even when a protein that binds to vitamin D in the blood was removed using gene editing, allowing vitamin D to reach tissues.
The researchers were surprised to find that vitamin D acts on epithelial cells in the intestine, leading to an increase in the abundance of a bacteria known as Bacteroides fragilis. This microbe appeared to enhance the mice’s immunity to cancer, as the transplanted tumors showed reduced growth. However, the exact mechanism by which this occurs is still unclear. To further investigate the role of Bacteroides fragilis, mice on a normal diet were given this bacteria and also exhibited better resistance to tumor growth. Interestingly, this effect was not seen in mice on a vitamin D-deficient diet.
Previous studies have suggested a potential link between vitamin D deficiency and an increased risk of cancer in humans, although the evidence has not been conclusive. To explore this further, the researchers analyzed data from 1.5 million people in Denmark, which indicated a correlation between lower vitamin D levels and a higher cancer risk. Another analysis of cancer patients showed that individuals with higher vitamin D levels were more likely to respond positively to immune-based cancer treatments. While Bacteroides fragilis is also found in the human microbiome, additional research is needed to determine whether vitamin D can enhance immune resistance to cancer through the same mechanism.
The researchers involved in the study emphasized the importance of further investigation before drawing definitive conclusions about the potential benefits of correcting a vitamin D deficiency for cancer prevention or treatment in humans. They highlighted the challenge of pinpointing the factors that distinguish a beneficial microbiome from a harmful one, with a specific focus on understanding how vitamin D supports a “good” microbiome. By uncovering these mechanisms, new opportunities may emerge for leveraging the microbiome’s influence on the immune system to prevent or treat cancer.
The study was funded by various organizations, including Cancer Research UK, the UK Medical Research Council, the Wellcome Trust, and the Intramural Research Program of the NCI, part of the NIH. Research Information Manager at Cancer Research UK, Dr. Nisharnthi Duggan, commented on the findings, emphasizing the need for further research to confirm the potential link between vitamin D and immune responses to cancer. She also highlighted the importance of maintaining adequate vitamin D levels through exposure to sunlight, diet, and supplements, while also emphasizing the importance of sun safety to reduce the risk of cancer.
Overall, this research sheds light on the potential role of vitamin D in modulating the gut microbiome to enhance immunity to cancer. While the findings in mice are promising, further research is needed to understand the underlying mechanisms and to determine whether similar effects can be observed in humans. This study represents an important step in elucidating the complex interplay between diet, gut bacteria, and immune responses to cancer, paving the way for new strategies to improve cancer prevention and treatment outcomes.
