Vitamin B12 Interactions

Long-term metformin use depletes vitamin B12 levels

Regular alcohol use impairs B12 absorption and can lead to deficiency.

Omeprazole suppresses gastric acid, which is required to cleave vitamin B12 from dietary proteins before it can bind intrinsic factor and be absorbed in the ileum. Long-term use (typically >2 years) is associated with measurably lower serum B12 levels and increased risk of clinical deficiency.

Esomeprazole, the S-isomer of omeprazole, profoundly suppresses gastric acid required to liberate vitamin B12 from food proteins, impairing its absorption with long-term use. Studies confirm a dose- and duration-dependent reduction in serum B12 with chronic PPI therapy.

Famotidine, an H2-receptor antagonist, reduces gastric acid secretion and thereby impairs cleavage of vitamin B12 from food proteins, which is required for B12 absorption. The effect is less pronounced than with PPIs but is clinically relevant with long-term use.

Cyanide in cigarette smoke binds to active forms of vitamin B12 (methylcobalamin and hydroxocobalamin), converting them to the inactive cyanocobalamin form which is excreted, and chronic smoking damages the gastric mucosa, reducing intrinsic factor production and B12 absorption.

Vitamin B12 and folate are interdependent coenzymes in the methionine cycle: methylfolate donates a methyl group to homocysteine while B12 (methylcobalamin) is the required cofactor for methionine synthase, the enzyme catalyzing the reaction. Adequate intake of both is needed to lower homocysteine, support DNA synthesis, and prevent the neurologic damage that high-dose folate alone can mask.

Choline (via its metabolite betaine) and vitamin B12 power the two parallel pathways that remethylate homocysteine to methionine: the choline-betaine-BHMT route and the folate-B12-methionine-synthase route. Adequate choline can compensate for low B12 or folate status by maintaining methylation through the BHMT pathway, supporting healthy homocysteine and SAMe levels.

Vitamin B6 (as pyridoxal 5'-phosphate) and vitamin B12 (as methylcobalamin) act as complementary coenzymes in one-carbon metabolism: B12 helps remethylate homocysteine back to methionine, while B6 routes excess homocysteine down the transsulfuration pathway to cysteine. Together they keep blood homocysteine within a healthier range than either nutrient does alone.