Folate, vitamin B6, multivitamin supplements, and colorectal cancer risk in women

The authors evaluated associations between intakes of folate and vitamin B-6 and colorectal cancer risk among women enrolled in a randomized trial on aspirin and vitamin E in disease prevention. At baseline (1992-1995), 37,916 US women aged >= 45 years who were free of cancer and cardiovascular disease provided dietary information. During an average of 10.1 years of follow-up (through February 20, 2004), 220 colorectal adenocarcinoma cases were documented. Total folate and vitamin B-6 intakes were not significantly associated with the risk of colorectal cancer. However, dietary intakes of folate and vitamin B-6 were significantly inversely associated with colorectal cancer risk among women who were not taking supplements containing folate and vitamin B-6. Multivariable relative risks among women in the highest quintiles of intake versus the lowest were 1.16 (95% confidence interval (CI): 0.76, 1.79) for total folate, 1.14 (95% CI: 0.77, 1.69) for total vitamin B-6, 0.46 (95% CI: 0.26, 0.81) for dietary folate, and 0.69 (95% CI: 0.41, 1.15) for dietary vitamin B-6. The use of multivitamin supplements was not related to colorectal cancer risk. These findings suggest that higher dietary intakes of folate and vitamin B-6 may reduce the risk of colorectal cancer in women. An alternative explanation is that other factors related to dietary intakes of folate and vitamin B-6 account for the inverse associations.