Dietary intake of vitamin B12 (cobalamin) and gastric cancer risk: a pooled analysis within the StoP Project

The effect of vitamin B ₁₂ (cobalamin) intake on gastric cancer is unclear. We investigated this association within the Stomach Cancer Pooling Project. Data from eight case-control studies within an international consortium were harmonized. Study-specific quartiles of dietary B ₁₂ intake (μg/day) were created using food frequency questionnaires and country-specific dietary composition tables. Odds ratios (ORs) and 95% confidence intervals (CIs) for the association between B ₁₂ and gastric cancer were calculated using multivariable logistic regressions adjusted by major sociodemographic and lifestyle factors. A random-effect meta-analysis pooling study-specific associations was also conducted. Secondary analyses were further adjusted for Helicobacter pylori (Hp ) and dietary factors. Analyses stratified by anatomical subsite, histological type, sex, age, smoking, alcohol, and socioeconomic status (SES) were performed. The main analysis included 2228 cases and 7096 controls. A borderline positive association was observed between vitamin B ₁₂ intake and gastric cancer (OR = 1.04, 95% CI = 0.99–1.10 per quartile of intake). Results only slightly attenuated after adjusting for Hp and dietary factors. No statistical heterogeneity was found by histology and anatomical subsite, despite a higher risk being observed for the intestinal subtype (OR = 1.10, 95% CI = 1.02–1.19 per quartile of intake). Women, the elderly, never smokers, no-to-low alcohol consumers, and individuals from high SES had an increased risk of gastric cancer with increasing B ₁₂ intake, with no significant heterogeneity. Overall, dietary vitamin B ₁₂ intake was not associated with gastric cancer risk, while a positive association was observed for intestinal-type gastric cancer and within specific population subgroups.