Anti-inflammatory Diet Index and Bladder Cancer Risk by Stage: A 22-Year Prospective Swedish Cohort Study (1998–2020)

BACKGROUND: Dietary patterns influencing systemic levels of inflammation have been proposed and investigated as possible determinants of cancer risk. We evaluated the association between the anti-inflammatory potential of diet and the risk of bladder cancer (BC). METHODS: The Anti-Inflammatory Diet Index (AIDI), composed of 16 food groups (11 anti- and 5 pro-inflammatory), was used to score dietary patterns in N=79,292 individuals derived from the Cohort of Swedish Men (COSM, established in 1997) and the Swedish Mammography Cohort (SMC, established in 1987). Dietary information was collected in 1997 and 2009; repeated-measure analyses used a cumulative-average AIDI. Incident BC cases were identified from the Swedish Cancer Register using ICD-10 code C67, and baseline study questionnaire was used to assess covariates. We estimated multivariable hazard ratios across AIDI quartiles using Cox models. RESULTS: After a 22-year follow-up, 1,165 individuals were diagnosed with BC, of whom 249 had non-muscle invasive (NMI) BC, 201 muscle invasive (MI) BC and 715 unknown stage. In repeated-measures analyses, the highest anti-inflammatory quartile (Q4) was associated with lower BC risk compared with the lowest quartile (Q1) (HR 0.74, 95% CI 0.61-0.89). Stratifying for tumour stage, there was a clear association between AIDI-score and MIBC (HR 0.35, 95% CI 0.22-0.57), but not for NMIBC (HR 0.86, 95% CI 0.57-1.28). CONCLUSIONS: An anti-inflammatory dietary pattern was associated with lower BC risk, with the clearest association for MIBC. IMPACT: These findings support the role of dietary inflammation in BC aetiology and suggest that promoting anti-inflammatory dietary patterns could contribute to cancer prevention strategies.