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

The effect of vitamin B12 (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 B12 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 B12 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 B12 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 B12 intake, with no significant heterogeneity. Overall, dietary vitamin B12 intake was not associated with gastric cancer risk, while a positive association was observed for intestinal-type gastric cancer and within specific population subgroups.