Huang D, Lei S, Wu Y, et al. - In this systematic review and meta-analysis, researchers ascertained the impacts of vitamin D and calcium on colorectal adenoma incidence, malignancy development and prognosis. By September 30, 2019, systematic literature searches (PubMed, Embase, and Cochrane Library databases) and hand searches have been performed. It included a total of 854,195 cases from 166 studies. Findings suggested an inverse association of the colorectal adenoma incidence with the circulating 25-hydroxyvitamin D [25(OH)D] level, vitamin D intake and calcium intake. Colorectal cancer (CRC) incidence was reduced by circulating 25(OH)D, vitamin D intake and calcium intake. The consumption of vitamin D against colorectal tumor was more effective for European and American populations. A significant dose-response association between intake of vitamin D or calcium and colorectal tumour incidence was noted. In colorectal adenoma incidence, malignant transformation and progression, vitamin D and calcium play additively chemopreventive roles, particularly for women and left-sided CRC patients.