Plasma folate concentrations and colorectal cancer risk: a case-control study nested within the Shanghai Men's Health Study.

Previous epidemiological studies of circulating folate concentration and colorectal cancer have reported inconsistent results. We evaluated associations of prediagnostic plasma folate concentration with colorectal cancer risk in a case-control study nested within the Shanghai Men's Health Study (2002-2010). Included herein are 288 cases who were diagnosed with incident colorectal cancer and 575 controls who were individually matched to cases on baseline characteristics. Folate concentrations in plasma were measured by microbiological assay. Multivariate conditional logistic regression was used to assess associations of plasma folate concentrations with colorectal cancer risk. Plasma folate was nonsignificantly but positively associated with colorectal cancer risk. Odds ratios (OR) and 95% confidence intervals (CI) were 1.38 (0.95-2.02) for the middle tertile of plasma folate concentrations and 1.33 (0.90-1.98) for the highest compared to the lowest tertile. The positive association reached statistical significance for the highest tertile of folate concentrations for men with late-stage colorectal cancer (OR = 2.66; 95% CI = 1.03-6.86) and for the middle tertile for cases diagnosed within the first 4 years after blood collection (OR = 1.72; 95% CI = 1.02-2.92) and for men in the high BMI group (OR = 1.88; 95% CI = 1.14-3.11). In our study population, where folic acid fortification of the food supply and vitamin supplement use are uncommon, plasma folate concentration was positively associated with colorectal cancer risk among men who may have had preneoplastic lesions. These findings need to be confirmed in studies with specific assessment of preneoplastic lesions and repeated measurements of folate level over time.