Chronic acid suppressive therapy can cause iron deficiency anemia.
Gastric acid is important for the absorption of iron, particularly dietary non-heme (plant-derived) iron. By inhibiting gastric acid secretion, PPIs and H2 blockers may impair the absorption of iron.
Cimetidine (Tagamet) has been shown to reduce absorption of iron from the diet. And there are reports of iron-deficient patients who didn't respond to iron supplements while taking omeprazole (Prilosec).
But long-term treatment with H2-blockers or PPIs is NOT associated with iron depletion or anemia in people with normal iron stores.