Case-control analysis of dietary folate and risk of bladder cancer.

Dietary folate, a water-soluble B vitamin found in a variety of fruits and vegetables, is of particular interest as a chemopreventive agent due to its role in DNA methylation and DNA synthesis and repair. We hypothesized that individuals with low folate intake would be at an increased risk for bladder cancer. Using an ongoing case-control study we assessed dietary folate in 409 incident bladder cancer patients and 451 healthy control subjects. A food-frequency questionnaire was used to estimate naturally occurring food folate (microg/kcal/day), dietary folate equivalents (DFE) from food sources (microg DFE/kcal/day), and DFE from all sources (microg DFE/kcal/day). Unconditional logistic regression analyses were used to estimate odds ratios (ORs) and 95% confidence intervals (CIs). Bladder cancer patients reported a statistically significant lower intake of folate than control subjects for food folate and DFE from food sources (P < 0.001) but not for DFE from all sources (P = 0.061). In the highest quartile of food folate intake there was a 54% reduced risk for bladder cancer (OR = 0.46; 95% CI = 0.29-0.73) after adjusting for age, gender, ethnicity, smoking, and total energy intake. Similarly, the highest quartile of intake was associated with a 59% reduced risk for DFE from food sources (OR = 0.41; 95% CI = 0.26-0.65) and a 35% reduced risk for DFE from all sources (OR = 0.65; 95% CI = 0.42-1.00). In the joint-effects analyses using never smokers with high folate intake as the reference group (OR = 1.0), heavy smokers with low food folate intake had a 2.31-fold (95% CI = 1.11-4.82) increased risk, whereas heavy smokers with high folate intake had a reduced OR of 1.31 (95% CI = 0.53-3.26). Although the ORs were not statistically significant, light smokers and high folate intake exhibited a protective effect (OR = 0.62; 95% CI = 0.20-1.94), whereas an increased risk was observed for light smoking and low folate intake (OR = 1.41; 95% CI = 0.57-3.45). These patterns were consistent for the joint effects of smoking and DFE from food sources and DFE from all sources. In summary, high intake of dietary folate was associated with an overall decrease in bladder cancer risk. These data may have important implications for cancer prevention; however, large, hypothesis-driven, population-based clinical trials will be required to confirm these findings.