Milk and the risk and progression of cancer.

Observational evidence suggests that nutritional factors contribute to a substantial proportion of cancer cases, and milk contains numerous bioactive substances that could affect risk and progression of cancer. Cancer results from multiple genetic and epigenetic events over time, so demonstrating a specific effect of nutrients or other bioactive food components in human cancer is challenging. Epidemiological evidence consistently suggests that milk intake is protective against colorectal cancer. Calcium supplements have been shown to reduce risk for recurrence of adenomatous polyps. Calcium supplementation has not been observed to reduce risk for colon cancer, although long latency and baseline calcium intake affect interpretation of these results. High calcium intake from both food and supplements is associated with increased risk for advanced or fatal prostate cancer. Results from epidemiological studies examining the relationship between intake of dairy foods and breast or ovarian cancer risk are not consistent. Animal studies have suggested that galactose may be toxic to ovarian cells, but results from epidemiological studies that have examined ovarian cancer risk and milk and/or lactose intakes are mixed. Dietary guidelines for cancer prevention encourage meeting recommended levels of calcium intake primarily through food choices rather than supplements, and choosing low-fat or nonfat dairy foods.