A new study has found evidence that the immune-stimulating properties of vitamin D are associated with a reduced risk of colon cancer. For the study, which was published in the journal Gut, researchers looked at blood samples from 942 people (taken prior to the onset of cancer) who took part in the Nurses’ Health Study and in the Health Professionals Follow-Up Study, both of which are long-term research projects involving thousands of participants. Of those 942 people, 318 eventually developed colon cancer, and 624 did not. Researchers hypothesized that, if vitamin D’s effect on the immune system contributed to a reduced risk of colon cancer, people with the highest vitamin D levels would be less likely to develop colon cancers enriched with a large number of immune cells, since those immune cells (partially activated by vitamin D) would help prevent colon cancer from developing. And indeed, this is what they found—high levels of vitamin D were associated with a lower incidence of the types of colon cancer that are most susceptible to an immune response. However, high vitamin D levels did not lower the risk of developing the types of colon cancer that are more resistant to an immune response. While more research is needed to confirm these results, the study is the first to provide evidence of vitamin D’s potential to prevent colon cancer in actual patients by stimulating the immune system.