The authors evaluated associations between intakes of folate and vitamin B6 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 B6 intakes were not significantly associated with the risk of colorectal cancer. However, dietary intakes of folate and vitamin B6 were significantly inversely associated with colorectal cancer risk among women who were not taking supplements containing folate and vitamin B6. 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 B6, 0.46 (95% CI: 0.26, 0.81) for dietary folate, and 0.69 (95% CI: 0.41, 1.15) for dietary vitamin B6.
The use of multivitamin supplements was not related to colorectal cancer risk. These findings suggest that higher dietary intakes of folate and vitamin B6 may reduce the risk of colorectal cancer in women. An alternative explanation is that other factors related to dietary intakes of folate and vitamin B6 account for the inverse associations.