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In this article, the authors review evidence from epidemiological studies, observational studies, one randomized trial and studies investigating the mechanisms through which vitamin D may help to prevent cancer. Studies have found that higher circulating 25(OH)D levels have been associated with lower incidences of various cancers including colon cancer, breast cancer, renal cancer, pancreatic cancer, and aggressive prostate cancer, among others. In terms of possible mechanisms, metabolites of vitamin D have been found to prevent “disjunction” of cells (one of 7 proposed stages of cancer etiology), and to offer benefits in the other stages as well (initiation, natural selection, overgrowth, metastasis, involution, and transition). In terms of supplementation, the reviewers found “�no unreasonable risks from intake of 2000 IU per day of vitamin D3�.” In addition, the authors state that raising the minimum year-around serum 25(OH)D level to 40-69 ng/ml (100-150 nmol/L) is projected to prevent approximately 58,000 new cases of breast cancer per year, 49,000 new cases of colorectal cancer per year, and � of deaths from these cancers in the U.S. and Canada. Raising the minimum 25(OH)D to this range is also projected to halve the case-fatality rates of patients with breast, colorectal, or prostate cancer. The authors conclude, “The time has arrived for nationally coordinated action to substantially increase intake of vitamin D and calcium.”