A new prospective study has reported a small positive association between folate intake and risk of breast cancer in postmenopausal women. The study was designed to investigate the associations between folate, folic acid, vitamin B-6, vitamin B-12, methionine, and alcohol intake and risk of breast cancer. Previous population studies examining the association between folate and risk of breast cancer have been inconclusive, and few have investigated how related nutrients may influence this association. The authors studied the associations of dietary folate (naturally occurring folate in food plus folic acid from fortification of foods), as well as total folate (food folate, folic acid from fortification, and folic acid from supplements) with risk of breast cancer. The study included 70,656 postmenopausal women enrolled in the Cancer Prevention Study II Nutrition Cohort from whom dietary information was obtained in 1992. A total of 3,898 of these participants developed breast cancer during the 13-year study period (1992 to June 2005).

Compared with the lowest fifth, the highest quintile of dietary folate intake was associated with a 12% higher risk of breast cancer. However, the test for trend was not statistically significant (higher folate intake did not necessarily translate into higher breast cancer risk). No relationships were found between total folate, vitamin B-6, or vitamin B-12 intake and risk of breast cancer. However, methionine (an essential amino acid) intake was found to be associated with lower breast cancer risk. The association of dietary folate with breast cancer was not influenced by other nutrients or alcohol consumption. The authors conclude that dietary folate intake might be positively associated with postmenopausal breast cancer. However, they note that no dose-response relation was observed. The extent to which increased supplement use and folate fortification contributes to breast cancer risk warrants further research.