**3.2 Vitamin D**

There is limited suggestive evidence that foods containing vitamin D, serum vitamin D, and supplemental vitamin D might decrease the risk of CRC [8]. For foods containing vitamin D, a dose-response meta-analysis showed a significant decreased risk for CRC. For supplemental vitamin D, the dose-response meta-analysis showed a significant decreased risk for colon cancer, whereas for plasma/serum vitamin D, the dose-response meta-analysis did not exhibit a significant association with CRC. Two published meta-analyses reported significant inverse associations. Hence, the WCRF/AICR, Continuous Update Project report, noted that plasma/serum vitamin D status can be influenced by sun exposure, obesity, seasonality, smoking, and measurement error. There is evidence of plausible mechanisms in humans [8]. Convincing data from epidemiologic and experimental studies support the potential chemopreventive effects of vitamin D against CRC development, although the evidence from randomized controlled trials (RCTs) is inconclusive [4].
