We identified 43 512 KPNC members with an incident diagnosis of vitamin B12 deficiency between January 1, 1997, and June 30, 2011. We excluded case patients lacking matched controls (n = 234), potential cases (n = 1751) and controls with diagnoses known to directly cause vitamin B12 deficiency, and potential cases (15 571) and controls who had taken PPIs or H2RAs for less than 2 years. This resulted in 25 956 cases and 184 199 controls in the final analyses. Case patients were predominantly female (57.4%), 60 years or older (67.2%), and of nonHispanic white race/ethnicity (68.4%) (Table 1).