Low folate levels are associated with reduced risk of colorectal cancer in a population with low folate status.

Background: A diet rich in folate is associated with a reduced colorectal cancer risk, whereas the role of circulating levels is less clear. The aim of this study was to relate prediagnostic plasma folate, vitamin B12, and homocysteine concentrations to the risk of colorectal cancer. Methods: This was a prospective case-control study of 331 cases and 662 matched controls nested within the population-based Northern Sweden Health and Disease Study. Median follow-up time from recruitment to diagnosis was 10.8 years. Results: Plasma folate concentrations were positively related to colorectal cancer risk; multivariate odds ratios were 1.62 [95% confidence intervals (CI), 1.08-2.42] and 1.42 (95% CI, 0.94-2.21) for the middle and highest versus lowest tertile, respectively. In subjects with follow-up <10.8 years, a statistically significant doubled risk was observed for the middle and highest versus lowest tertile, whereas findings for longer follow-up times were null. A positive risk relationship was also observed for tumor stage III-IV but not I-II. Plasma vitamin B12 concentrations were inversely associated with rectal cancer risk. Homocysteine was not significantly related to colorectal cancer risk. Conclusions: In this population-based, nested case-control study, low plasma folate concentrations were associated with a reduced colorectal cancer risk. This protective role was mainly observed in subjects with higher tumor stage or shorter follow-up time between recruitment and diagnosis. Low circulating folate status may protect against colorectal cancer or suppress progression of preneoplastic or neoplastic lesions. Impact: These findings mayhave relevance for the ongoing debate about mandatory folic acid fortification of flour. (C) 2014 AACR.