C15:0 and C17:0 partially mediate the association of milk and dairy products with bladder cancer risk.

The relationship between saturated fatty acids (SFA) and bladder cancer (BC) risk has been conflicting. Our aim was to investigate the relationship between erythrocyte membrane SFA and BC risk. A total of 404 participants were enrolled in the study (including 112 cases and 292 controls). A validated food frequency questionnaire was used to assess the food intake. The constitutive composition of fatty acids in the erythrocyte membrane was measured by gas chromatography. After adjustment for BC risk factors, SFA had no significant association with BC risk. However, C18:0 was positively linked with BC risk with an odds ratio (OR; 95% CI) of 2.99 (1.37-6.53). In contrast, very-long-chain saturated fatty acids (VLCSFA), especially C24:0, were negatively related to BC risk with an OR (95% CI) of 0.28 (0.12-0.65) for VLCSFA and 0.33 (0.15-0.75) for C24:0. Higher total odd-chain SFA (C15:0 and C17:0) were associated with a lower risk of BC with OR (95% CI) of 0.18 (0.076-0.44), 0.18 (0.068-0.47), 0.34 (0.14-0.81), respectively. After subgroup analysis, the protective effects C15:0 and C17:0 were still remained. Receiver operating characteristic analysis displayed that the combination of C15:0 and C17:0 indexes increased the accurate predictive rate of BC risk. Further mediation effect analysis showed that C15:0 and C17:0 could be used as partial mediation effectors for milk and dairy products and bladder carcinogenesis. Overall, the combination of odd-chain SFA (C15:0 and C17:0) in the erythrocyte membrane could serve as a reliable mediator and predictor, indicating a relationship between a high intake of milk and dairy products and a lower risk of BC.