Vitamin B12: A Comprehensive Review of Natural vs Synthetic Forms of Consumption and Supplementation.

Vitamin B12, also known as cyanocobalamin, methylcobalamin, and adenosylcobalamin, is an essential vitamin that can be primarily obtained through the human diet. Although animal-based foods supply adequate B12 for most people, deficiency remains common in older adults, vegetarians and vegans, and in those with gastrointestinal disease or malabsorption. Deficiency can lead to megaloblastic anemia, neurologic symptoms, and pregnancy complications. In healthy individuals, supplementation raises serum B12 levels to a similar extent as dietary intake; however, in disease states such as megaloblastic anemia, supplementation is required because diet alone is not sufficient. Interest has grown in how natural dietary forms, such as methylcobalamin, compare with the widely used synthetic form, cyanocobalamin, with respect to absorption, metabolism, and clinical effect. This comprehensive review summarizes B12 physiology, sources, absorption, and the clinical picture of deficiency, and compares natural and synthetic forms in common patient scenarios. We also note practical questions for future work, including long-term outcomes of supplementation and whether prophylaxis is useful in high-risk groups.