What nutrient deficiency is most likely with prolonged use of a proton pump inhibitor?

Proton pump inhibitors (PPIs) are commonly used medications that reduce gastric acid production, which can affect the absorption of certain nutrients in the gastrointestinal tract. Among these, vitamin B12 is particularly significant because it requires an acidic environment in the stomach for adequate absorption.

Long-term use of PPIs can lead to a decreased level of stomach acid, subsequently impairing the absorption of vitamin B12 from dietary sources. This deficiency can result in various health issues, including anemia and neurological problems, due to vitamin B12's critical role in DNA synthesis and maintaining nerve health.

In contrast, while deficiencies in magnesium, folic acid, and vitamin B6 can occur with certain conditions or medications, they are not as directly linked to the action of PPIs as vitamin B12 is. Thus, the most likely nutrient deficiency resulting from prolonged PPI use is indeed vitamin B12.