Consumption of Processed Meat and Unprocessed Red Meat and Risk of Bladder Cancer: A Pooled Analysis of 30 Cohort Studies

Background: Processed meat and unprocessed red meat are considered carcinogenic and 'probably carcinogenic' to humans, respectively, but findings for bladder cancer remain inconsistent. Objectives: We assessed associations between processed meat and unprocessed red meat intake and bladder cancer risk using data from the Pooling Project of Prospective Studies of Diet and Cancer. Methods: Associations with bladder cancer risk were assessed using individual-level data from 30 cohort studies from North America, Europe, Australia and Asia. Diet was assessed at enrolment using validated food frequency questionnaires or diet histories. Following a pre-specified analysis plan, study- and sex-specific hazard ratios (HRs) and 95% confidence intervals (CIs) were estimated using Cox regression, adjusted for smoking status and duration and other potential confounders, and pooled using inverse-variance-weighted random-effects meta-analysis. Results: During median follow-up across cohorts of 8-29 years, among 2,575,971 participants, 20,780 were diagnosed with bladder cancer. Processed meat intake was associated with increased bladder cancer risk (HR comparing ≥40 with <5 g/day = 1.08; 95% CI: 1.02-1.15; HR per 20 g/day = 1.02; 95% CI: 1.00-1.03). Weaker evidence of association with increased risk was also observed for unprocessed red meat (HR comparing ≥100 with <20 g/day = 1.06; 95% CI: 1.00-1.13; HR per 50 g/day = 1.01; 95% CI: 0.99-1.03). There was no evidence of heterogeneity by study, sex, or region. Conclusions: Higher intakes of processed meat and unprocessed red meat were associated with a small increase in risk of bladder cancer. These findings are consistent with existing public health recommendations to limit consumption of red and processed meat.