Processed meat, unprocessed red meat, poultry, seafood, and egg intake and stomach cancer risk: a pooled analysis of 20 cohorts

BACKGROUND: Processed meat is classified as a carcinogen and unprocessed red meat a probable carcinogen, but their associations with stomach cancer are not established. We evaluated intakes of these food groups and poultry, seafood, and eggs in relation to stomach cancer risk. METHODS: Individual-level data for 1 100 370 females and 891 919 males from 20 cohorts were analysed. Diet was assessed at baseline by using food-frequency questionnaires or diet histories generally covering the past year and harmonized across studies. We used Cox regression to estimate multivariable-adjusted study- and sex-specific hazard ratios (HRs) and 95% confidence intervals (CIs) for associations with each food group and combined study-specific estimates by using random-effects meta-analysis. We repeated analyses using an aggregated dataset combining all studies. RESULTS: During follow-up (mean = 8-23 years across studies), 8561 invasive gastric adenocarcinomas were diagnosed. Processed meat intake showed weak evidence of an overall association with stomach cancer risk (HR, 1.15 for ≥45 vs <3 g/day; 95% CI, 1.00-1.32 and HR, 1.03 per 25-g/day increment; 95% CI, 0.99-1.07). This association was limited to current smokers (Pinteraction = .01) and differed by geographic region, with evidence for an association in Australian and European studies and no association observed in Asian studies (Pinteraction = .02). Positive associations with stomach cancer were observed for egg intake; no association was found for unprocessed red meat, poultry, or seafood. CONCLUSION: Higher processed meat intake was associated with a modestly increased risk of stomach cancer among current smokers, although residual confounding by smoking dose remains possible. Findings for eggs warrant further investigation.