Gastric acid is necessary for absorption of vitamin B12. Researchers studied those who took proton pump inhibitors or histamine 2 receptor antagonists to reduce stomach acid for more than two years. They found a 65% increased risk of B12 deficiency when compared to nonusers. The risk increased even more when taking higher doses. The good news: the association weakened after discontinuation of the drug use.
PositiveTip: Use acid-suppressing drugs only if absolutely necessary, especially if your intake of vitamin B12 is limited (total vegetarian).