**Background:** Vitamin B12 (VB12), or cobalamin, is an essential water-soluble vitamin that plays critical roles in blood cell synthesis, cognitive function, and cardiovascular health. It is primarily found in animal-derived foods, posing a significant challenge for strict vegetarians and vegans who are at high risk of deficiency. The absorption of VB12 is complex, relying on intrinsic factor and absorption in the ileum, and can be impaired by various conditions. This review aims to provide a comprehensive overview of recent advances in dietary sources, health benefits, encapsulation methods, food fortification strategies, and sensor-based detection techniques for VB12.
**Methods:** The authors conducted a critical review of the literature, synthesizing findings from multiple studies on VB12. They examined the chemical structure and dietary sources of VB12, detailing its presence in animal products (e.g., liver 26–58 μg/100g, beef and lamb 1–3 μg/100g, fish 3.0–8.9 μg/100g) and trace amounts in some plant-based sources like microalgae and fermented foods. The review covers the absorption mechanism, including the role of intrinsic factor and transcobalamin II, and discusses bioavailability assays such as the Schilling test, C-CobaSorb test, and newer methods using 14C-labeled VB12. The health benefits section summarizes VB12's role in DNA synthesis, homocysteine metabolism, and prevention of megaloblastic anemia, cardiovascular diseases, cognitive decline, and optic neuropathy. The encapsulation section details both microencapsulation (spray-drying, spray-chilling, electrospinning, double emulsions) and nanoencapsulation (nanovesicles, nanoemulsions, nanoparticles) techniques, including specific examples like zein-based microstructures, solid lipid microparticles, and soy protein nanoparticles. The food fortification section reviews direct enrichment of salt, sugar, wheat flour, and dairy products, as well as enrichment with encapsulated VB12. Finally, the biosensing section covers fluorescent carbon dot nanosensors, nanocluster-based fluorescent probes, and electrochemical sensors, providing a table of electrode materials and their performance metrics.
**Key Results:** The review reports a ~62% prevalence of VB12 deficiency among vegetarians, with deficiency rates varying from 25% to 86% in pregnant women, 21% to 41% in children/adolescents, and 11% to 90% in the elderly. For encapsulation, spray-drying of VB12 with modified chitosan yielded a ~57% powder yield and superior retention after 6 months (<20% loss). Co-microencapsulation of VB12 and vitamin D3 in a gum acacia/Hi-Cap/maltodextrin matrix resulted in a 151% increase in VB12 bioavailability in rats. Nanoencapsulation using soy protein nanoparticles (30 nm) increased intestinal transport of VB12 up to 4-fold. For food fortification, co-extrusion of VB12 with iron in salt retained over 98% of VB12 after 6 months. In bakery products, VB12 retention was highest in flat-bread (chapattis) at 90.6%, followed by bread at 79.7%, cake at 35.8%, cookies at 24.5%, and oil-fried flat-bread (poori) at 13.9%. For biosensing, a carbon quantum dot-based sensor achieved a limit of detection (LOD) of 210 pM for VB12 over a range of 1 nM to 20 μM. An electrochemical sensor using an Au-PPyNPs@f-CNTs nanocomposite on a glassy carbon electrode showed a linear range of 0 to 85 μM, an LOD of 0.9 nM, and a sensitivity of 4.3597 μA/μM. Another electrochemical sensor using a Pt-modified Cu(HBTC)(4,4′-bipy)·3DMF electrode achieved an LOD of 50 nM and a linear range of 0.1–188.2 μM.
**Clinical Implications:** The findings underscore the critical need for VB12 supplementation in populations at risk, particularly vegetarians, vegans, the elderly, pregnant women, and individuals with malabsorption disorders. The development of effective encapsulation and fortification strategies can significantly improve VB12 stability, bioavailability, and controlled release, thereby enhancing the efficacy of supplementation and food-based interventions. The emergence of sensitive, portable biosensors for VB12 detection offers the potential for point-of-care diagnostics and personalized nutritional monitoring, which could improve the management of VB12 deficiency and its associated health consequences, including megaloblastic anemia, cardiovascular disease, cognitive decline, and optic neuropathy. The review also highlights the need for further research into the long-term health effects of high-dose VB12 supplementation and the potential risks, such as an increased risk of lung cancer in certain populations.