If your patient is on long-term acid-suppression therapy with a proton pump inhibitor (PPI) or histamine 2 (H2) blocker, be concerned about vitamin B12 deficiency. That is the message from a new study by Kaiser Permanente. Chronic use of acid-suppressing medications is common with hundreds of millions of prescriptions written every year as well as widespread over-the-counter use. The researchers found that among patients diagnosed with B12 deficiency, 12% were dispensed ≥ 2 year’s supply of a PPI, and 4.2% were dispensed ≥ 1 year’s supply or more of an H2 antagonist, which was significantly higher than the rate of patients without B12 deficiency (odds ratio [OR] of B12 deficiency with PPI 1.65 95% confidence interval (CI), 1.58-1.73); OR of B12 deficiency with H2 blocker 1.25 (95% CI, 1.17-1.34). The authors conclude that previous and current gastric acid suppression was significantly associated with the presence of B12 deficiency (JAMA 2013;310:2435-2442). Vitamin B12 deficiency is probably more common than we think and the long-term effects can be devastating. It is good to keep this in mind for patients on chronic acid-suppressing medications.