Dietary folate, methionine, riboflavin, and vitamin B-6 and risk of sporadic colorectal cancer.

Adequate intake of folate, methionine, riboflavin, and vitamin B-6 may prevent aberrant DNA methylation and thereby protect against colorectal cancer (CRC). However, previous epidemiological studies investigating associations between dietary intakes of these nutrients and CRC have been inconsistent. We investigated the associations between intakes of folate, methionine, riboflavin, and vitamin B-6 and CRC risk, accounting for the sublocalization of the tumor. Within the Netherlands Cohort Study on diet and cancer (n = 120,852), 2349 cases and 4168 subcohort members were available for data analyses from a follow-up period of 13.3 y after baseline. Gender-specific adjusted incidence rate ratios (RR) were calculated over quintiles of dietary intake in case-cohort analyses. Folate intake was not associated with CRC risk in either men or women. However, methionine was associated with decreased risk of proximal colon cancer among men (RR = 0.57 for highest vs. lowest quintile of intake; P-trend = 0.03) and rectal cancer among women (highest vs. lowest quintile; RR = 0.45; P-trend = 0.05). Riboflavin tended to be associated with decreased proximal colon cancer risk among women (RR = 0.61; P-trend = 0.07). Conversely, there was a strong positive association between vitamin B-6 and rectal cancer among women (RR = 3.57; P-trend = 0.01). Our findings suggest that relatively high methionine intake may protect against proximal colon cancer in men and rectal cancer in women but that folate may not have a protective effect. This is the 2nd prospective cohort study in which vitamin B-6 intake was associated with increased risk of rectal tumors in women, which might suggest that this vitamin enhances rectal cancer in women.