What is vitamin B12 and what is it used for?

Introduction

Vitamin B12 (cobalamin) is an essential, water-soluble micronutrient with a unique corrin ring and a central cobalt atom. It functions as a critical cofactor in metabolic reactions that support normal energy-yielding metabolism, red blood cell formation, nervous system maintenance, and homocysteine regulation. Because biologically active B12 is produced by certain microorganisms and accumulates mainly in animal-derived foods, understanding sources, absorption, and supplementation is important for many populations.

Biological roles and recognized benefits

Methylcobalamin and adenosylcobalamin are the active intracellular forms that participate in one-carbon metabolism and the conversion of methylmalonyl-CoA to succinyl-CoA, respectively. These reactions underpin B12’s contributions to normal psychological function, reduction of tiredness and fatigue, and maintenance of nervous system integrity. Regulatory authorities recognize specific functions of B12 when adequate intake is maintained; evidence supports beneficial effects primarily when insufficiency is present or when supplementation corrects a documented deficiency.

Who is at risk of deficiency and common symptoms

Groups at higher risk include strict vegetarians and vegans who do not use fortified foods or supplements, older adults with reduced gastric acid or intrinsic factor production, and people with gastrointestinal conditions such as pernicious anemia, ileal resection, or chronic inflammatory bowel disease. Long-term use of medications like proton pump inhibitors or metformin has also been associated with lower B12 levels. Symptoms range from fatigue, pallor, and macrocytic anemia to neurologic signs such as numbness, balance difficulties, and cognitive changes. Because neurologic damage can become less reversible over time, clinical assessment and laboratory testing (serum B12, methylmalonic acid, homocysteine when indicated) are important.

Absorption and implications for supplementation

Dietary B12 must be released from protein in the stomach, bind intrinsic factor, and be taken up in the terminal ileum. Disruption at any step—reduced acid, intrinsic factor deficiency, ileal disease, or bacterial overgrowth—reduces bioavailability. High-dose oral supplementation can allow passive absorption in some cases, while intramuscular injections bypass the gut and are used for severe deficiency or confirmed malabsorption. Oral supplements commonly use cyanocobalamin (stable, converted in the body) or methylcobalamin (an active form). Evidence comparing sublingual to oral preparations is mixed; choice of form should reflect absorption capacity and clinical goals.

Vegan sources and practical guidance

Reliable plant-based B12 comes from fortified foods such as certain plant milks, fortified cereals, nutritional yeast, and some meat alternatives. Many vegans choose a regular supplement to ensure consistent intake. Pregnant and breastfeeding individuals should verify adequate intake because fetal and infant stores depend on maternal status. For broader nutritional planning, resources on related nutrients such as magnesium dosage by age and gender and comparisons like gummy vs traditional vitamins can inform choices; for discussion of gummy formulations specifically, see this analysis of gummy vitamins.

Conclusion

Vitamin B12 is essential for specific, well-documented physiological functions. Maintaining adequate status relies on appropriate dietary sources, fortified foods, or supplementation when risk factors for deficiency exist. Clinical testing and professional advice guide optimal strategies for dosing and delivery, particularly when absorption is impaired or symptoms suggest deficiency.