{"entity":{"id":"vitamin-b12-supplements","kind":"technology","name":"Vitamin B12 supplements","aka":["Cyanocobalamin","Cobalamin"],"tldr":"Vitamin B12 is essential, and people who lack it, for example after stomach surgery or on long-term metformin or acid-suppressing tablets, need it replaced. Taken as an extra by people who are not deficient it has not been shown to prevent cancer or improve fatigue, and one study linked B12 supplements during chemotherapy with worse outcomes.","summary":"Memorial Sloan Kettering's About Herbs entry describes B12 as essential for nerve function, DNA synthesis and blood formation, with deficiency common after gastric surgery, with malabsorption, on proton pump inhibitors, H2 blockers or metformin, on strict vegan diets and in older people; deficiency causes anaemia and neurological problems and is treated with B12. For people who are not deficient the evidence is weaker. Studies of B vitamins for cancer prevention are mixed, and MSK notes that long-term supplementation may increase the risk of lung or colorectal cancer. Preliminary data suggest B12 may reduce aromatase-inhibitor joint and muscle symptoms, but an analysis found that taking B12 or iron supplements during chemotherapy was significantly associated with poorer outcomes, which needs further study. Folic acid above the upper intake limit can mask B12 deficiency. Gastrectomy, some bowel resections and long-term metformin are common in people with cancer, so checking B12 levels and treating a measured deficiency is good care; taking it without a reason is not.","status":"phase-2","asOf":"2026-11-04","links":[{"label":"MSK About Herbs: Vitamin B12 (page last updated 2 February 2022)","url":"https://www.mskcc.org/cancer-care/integrative-medicine/herbs/vitamin-b12"}],"tags":["complementary","supportive-care","evidence:insufficient"],"related":["folic-acid-supplements","vitamin-b6-pyridoxine"],"cancers":[],"sections":["supportive-care","nutrition-lifestyle"],"technologies":["integrative-oncology","dietary-supplements-treatment-interactions"],"targets":[],"drugs":[],"companies":[],"institutions":[],"pathways":[],"terms":["aromatase-inhibitor"],"trials":[],"people":[],"bottlenecks":["b-toxicity-qol"],"keyPapers":[],"journals":[],"dependsOn":[],"notes":[],"principle":"A cofactor for methionine synthase and methylmalonyl-CoA mutase; absorption depends on stomach acid and intrinsic factor, which is why stomach surgery and acid suppression cause deficiency.","strengths":["Treating measured deficiency is standard care","Preliminary signal for aromatase-inhibitor joint symptoms"],"limitations":["No cancer prevention benefit; possible increased lung and colorectal risk with long-term use","Supplement use during chemotherapy associated with poorer outcomes in one analysis","Folic acid can hide a deficiency"]},"route":"/technologies/vitamin-b12-supplements/","neighbours":{"technology":[{"id":"dietary-supplements-treatment-interactions","kind":"technology","name":"Dietary supplements during cancer treatment: interactions and harms","route":"/technologies/dietary-supplements-treatment-interactions/"},{"id":"integrative-oncology","kind":"technology","name":"Evidence-based integrative oncology","route":"/technologies/integrative-oncology/"},{"id":"folic-acid-supplements","kind":"technology","name":"Folate and folic acid supplements","route":"/technologies/folic-acid-supplements/"},{"id":"vitamin-b6-pyridoxine","kind":"technology","name":"Vitamin B6 (pyridoxine) for hand-foot syndrome and other uses","route":"/technologies/vitamin-b6-pyridoxine/"}],"section":[{"id":"nutrition-lifestyle","kind":"section","name":"Diet, Exercise & Lifestyle","route":"/fronts/nutrition-lifestyle/"},{"id":"supportive-care","kind":"section","name":"Supportive Care & Survivorship","route":"/fronts/supportive-care/"}],"term":[{"id":"aromatase-inhibitor","kind":"term","name":"Aromatase inhibitor","route":"/terms/aromatase-inhibitor/"}],"bottleneck":[{"id":"b-toxicity-qol","kind":"bottleneck","name":"Toxicity and quality of life are undervalued","route":"/bottlenecks/b-toxicity-qol/"}]}}