The effects of dietary folate on MNU-induced mammary tumourigenesis

Results from recent epidemiological studies suggest that dietary folate intake is inversely related to the risk of breast cancer. Three distinct animal studies were performed to define a causal relationship between dietary folate status and the risk of breast cancer in the well-defined MNU-induced rat model of mammary tumourigenesis. Dietary folate status had no significant effect on the initiation phase of MNU-induced mammary carcinogenesis. By contrast, dietary folate deficiency of a moderate degree significantly suppressed, whereas dietary folate supplementation at four times the basal dietary requirement did not significantly modulate, the promotion/progression phase of mammary tumourigenesis. Altered global DNA methylation as an underlying molecular mechanism involved in folate-mediated mammary tumourigenesis was not operative in these studies. These data suggest that folate supplementation should not be routinely provided to reduce breast cancer risk in humans until future studies clarify the role of folate in the development of breast cancer.