Specifically, vitamin D exerts direct effects on the gastrointestinal tract by modulating vitamin D receptor (VDR) expression (increased expression in early stages of CRC and decreased expression in late-stage CRC) (7) and expression of the vitamin D activation enzyme CYP27B1 (increased) during different stages of CRC progression (8, 9). The gene discussed is VDR; the disease is colorectal carcinoma.