Previous studies have suggested that increased folate intake may be associated with a reduced risk of breast cancer, but this association was not replicated by large studies that followed study participants prospectively. In addition, a common genetic change in the gene encoding a key enzyme in folate metabolism, called MTHFR, can lead to low folate levels in the body and therefore could be associated with breast cancer risk.

Sarah J. Lewis, of the University of Bristol in the United Kingdom, and colleagues searched Medline and the ISI Web of Knowledge for studies on folate intake and breast cancer risk. They assessed the relationship between folate intake and disease occurrence, being careful to note observational bias or error. They also examined the link between the common MTHFR polymorphism and breast cancer risk.

The authors found that many of the studies were subject to publication bias, dietary assessment measurement errors, confounding by factors associated with dietary intake, or recall bias. They did not observe a link between the common MTHFR alterations and breast cancer risk. "We have reviewed the evidence from epidemiologic and genetic studies and found no consistent or reliable evidence to support a role of dietary folate in breast cancer prevention," the authors write.

In an accompanying editorial, Han-Yao Huang, Ph.D., of the Johns Hopkins Bloomberg School of Public Health in Baltimore, Md., writes, "The strength of evidence on the association between folate intake and breast cancer risk is very low, suggesting that any estimate of effect is very uncertain."; Source: Journal of the National Cancer Institute