However, not all the research studies demonstrated beneficial effects of VD on intestinal barrier function, Mandle et al. in their randomized controlled trial concluded that no evidence was found for incremental effects of supplemental VD on CLD-1, OCDN, and MUC12 levels in the normal colorectal mucosa of patients at increased risk for colorectal cancer (35). Here, CLDN1 is linked to colorectal cancer.