What is Vitamin B12?
This post was written with Consensus AI Academic Search Engine – please read our Disclaimer at the end of this article. Vitamin B12, also known as cobalamin, is a crucial water-soluble vitamin that plays a significant role in various bodily functions, including DNA synthesis, cellular metabolism, and the maintenance of neurological health. Despite its importance, vitamin B12 deficiency is relatively common and can lead to severe health issues if not addressed. Other names include: Adenosylcobalamin, Adénosylcobalamine, B-12, B12, B Complex Vitamin, Bedumil, Cobalamin, Cobalamin Enzyme, Cobalamine, Cobamamide, Cobamin, Cobamine, Coenzyme B12, Co-Enzyme B12, Coenzyme B-12, Co-Enzyme B-12, Complexe Vitaminique B, Cyanocobalamin, Cyanocobalamine, Cyanocobalaminum, Cycobemin, Dibencozide, Dibencozida, Hydroxocobalamin, Hydroxocobalamine, Hydroxocobalaminum, Hydroxocobemine, Hydroxocobémine, Idrossocobalamina, Mecobalamin, Methylcobalamin, Méthylcobalamine, Vitadurin, Vitadurine, Vitamina B12, Vitamine B12.
Functions of Vitamin B12
Vitamin B12 is essential for several biochemical processes in the body. It acts as a coenzyme in the conversion of homocysteine to methionine, a reaction that is vital for DNA methylation and synthesis. Additionally, it is involved in the conversion of methylmalonic acid to succinyl-CoA, a critical step in mitochondrial metabolism1 2 4.
Sources of Vitamin B12
The primary dietary sources of vitamin B12 are animal-derived foods such as meat, fish, dairy products, and eggs. Plant-based sources are generally inadequate, making vegetarians and vegans more susceptible to deficiency. Fortified foods and supplements are often recommended for individuals who do not consume animal products9.
Bioavailability and Absorption
Vitamin B12 absorption is a complex process that involves the intrinsic factor, a protein secreted by the stomach lining. The bioavailability of vitamin B12 varies depending on the source, with animal products generally offering higher absorption rates compared to plant-based sources. For instance, the bioavailability from fish, sheep, and chicken meat ranges from 42% to 89%, while it is significantly lower from eggs9.
Deficiency and Its Consequences
Vitamin B12 deficiency can manifest in various ways, ranging from subclinical symptoms to severe neurological and hematological disorders. Common causes of deficiency include inadequate dietary intake, malabsorption, and certain medical conditions that affect the stomach or intestines1 2 4.
Neurological and Cognitive Effects
Deficiency in vitamin B12 can lead to neurological issues such as cognitive decline, memory loss, and even dementia. Studies have shown that higher levels of vitamin B12 are associated with better cognitive function in older adults, although the evidence is not conclusive3 8.
Hematological Effects
Vitamin B12 is crucial for red blood cell formation. A deficiency can lead to megaloblastic anemia, characterized by the production of abnormally large and dysfunctional red blood cells. This condition can cause symptoms like fatigue, weakness, and shortness of breath1 4.
Metabolic Effects
Recent research has indicated that vitamin B12 deficiency may also impact glucose metabolism, potentially contributing to conditions like diabetes mellitus. In animal studies, B12 deficiency has been linked to glucose intolerance and altered insulin levels5.
Diagnosis and Management of Vitamin B12
Diagnosing vitamin B12 deficiency typically involves measuring serum levels of total B12, holo-transcobalamin, homocysteine, and methylmalonic acid. However, the exact cut-offs for defining deficiency are still debated1 4.
Treatment
Management of vitamin B12 deficiency usually involves supplementation, either orally or via intramuscular injections. The choice of treatment depends on the severity of the deficiency and the underlying cause1 2.
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Adverse Effects of Vitamin B12
Adverse Effects from Intramuscular Injections
Intramuscular injections of Vitamin B12 can cause side effects, potentially due to contaminants in the preparation rather than the vitamin itself1.
Impact of Vitamin B12 Deficiency
Severe Vitamin B12 deficiency can impair lipid profiles, induce adiposity, and lead to adverse gestational outcomes, including anemia, reduced conception rates, smaller litter sizes, and increased neonatal mortality2.
Deficiency across generations can adversely affect long-chain polyunsaturated fatty acid status and cardiometabolic markers, increasing triglycerides and systolic blood pressure while lowering cholesterol levels3.
In pregnant women, Vitamin B12 deficiency is associated with higher risks of neural tube defects, gestational diabetes, pre-eclampsia, lower birth weight, and adverse long-term health outcomes in offspring, such as cognitive impairments and insulin resistance6.
Adverse Effects from Supplementation
Oral Vitamin B12 supplementation is generally considered safe, with low-quality evidence suggesting it has similar effects to intramuscular administration in normalizing serum levels, but with lower associated costs4.
High doses of Vitamin B12 supplementation in vegans and vegetarians with marginal deficiency can effectively restore serum concentrations and improve metabolic markers without significant adverse effects10.
Ineffectiveness in Certain Conditions
Vitamin B12 supplementation does not significantly improve cognitive function, depressive symptoms, or idiopathic fatigue in patients without advanced neurological disorders or overt deficiency5.
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How has Vitamin B12 Improved Patient Outcomes?
Diabetic Neuropathy Improvement
Vitamin B12 supplementation significantly improves neurophysiological parameters, pain scores, and quality of life in patients with diabetic neuropathy1 3.
Hepatitis C Treatment Enhancement
Adding Vitamin B12 to standard antiviral therapy for chronic hepatitis C significantly increases sustained viral response rates, especially in patients with difficult-to-treat genotypes and high baseline viral loads2.
Cognitive Function in Elderly
Vitamin B12 supplementation improves cognitive performance, particularly in attention, calculation, and visual-constructional abilities, in middle-aged and elderly patients with cognitive impairment4.
Exercise Tolerance in COPD
Vitamin B12 supplementation, when combined with exercise training, enhances exercise tolerance in patients with advanced COPD8.
COVID-19 Outcomes
A combination of Vitamin D, magnesium, and Vitamin B12 reduces the need for oxygen therapy and intensive care support in older COVID-19 patients7.
Oral vs. Intramuscular Administration
Oral Vitamin B12 is as effective as intramuscular administration in normalizing serum B12 levels and is preferred by patients due to lower costs and ease of use9 10.
Psychosis and Neurocognition
While Vitamin B12 supplementation reduces homocysteine levels, it does not significantly improve overall psychopathology or global neurocognition in first-episode psychosis, though it may benefit specific cognitive domains like attention/vigilance in certain subgroups6.
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Vitamin B12 Mechanisms of Action
Cofactor Role in Enzymatic Reactions
Vitamin B12 acts as a cofactor for methionine synthase (MTR), which is essential for the synthesis of methionine, a precursor of S-Adenosylmethionine (SAM), a universal methyl donor involved in epigenomic regulation1 4 9.
It is also a cofactor for methylmalonyl-CoA mutase (MCM), which catalyzes the conversion of L-methylmalonyl-CoA to succinyl-CoA, a critical step in the metabolism of certain amino acids and fatty acids5 9.
Mechanisms of Catalysis
In adenosylcobalamin-dependent isomerases, the cobalt-carbon bond of B12 ruptures homolytically, while in methylcobalamin-dependent methyltransferases, it cleaves heterolytically2 9.
The enzyme CblC catalyzes the reductive decyanation of cyanocobalamin and the dealkylation of alkylcobalamins, showcasing the multifunctionality of B12-processing enzymes7.
Neurological and Cellular Effects
Vitamin B12 deficiency can lead to neurological symptoms due to impaired methionine synthesis and subsequent DNA methylation issues, which affect cell proliferation, differentiation, and apoptosis1 4.
It inhibits tau protein fibrillization by binding to cysteine residues, preventing tau aggregation and potentially mitigating neurodegeneration3.
Antioxidant Properties
Vitamin B12 exhibits intrinsic antioxidative activity, particularly within mitochondria, which may help in conditions like diabetic peripheral neuropathy by reducing oxidative stress4.
Impact on Microbiota
Vitamin B12 modulates the transcriptional activities of skin microbiota, influencing conditions like acne by altering the production of inflammation-inducing compounds6.
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Common Complaints Associated with Vitamin B12 Use
Ineffectiveness in Cognitive and Depressive Symptoms
Vitamin B12 supplementation does not significantly improve cognitive function or depressive symptoms in patients without advanced neurological disorders or overt deficiency1 7.
Association with Metformin Use
Long-term use of metformin is associated with an increased risk of vitamin B12 deficiency, which can lead to anemia and peripheral neuropathy. Routine testing for B12 levels in metformin-treated patients is recommended2 5.
Neurological and Hematological Issues
Vitamin B12 deficiency can cause neurological symptoms (e.g., cognitive impairment, memory loss, mental depression) and hematological issues (e.g., megaloblastic anemia, neutropenia, thrombocytopenia)3 5 6 7 8.
Gastrointestinal Complaints
Symptoms such as flatulent dyspepsia and gastrointestinal discomfort are reported in individuals with B12 deficiency, particularly in those with chronic atrophic gastritis8.
Metabolic and Glucose Homeostasis Issues
B12 deficiency may contribute to impaired glucose homeostasis, glucose intolerance, and increased ketogenesis, potentially promoting metabolic disorders like diabetes mellitus4.
General Fatigue and Growth Issues in Children
Common complaints in children with B12 deficiency include fatigue, loss of appetite, growth retardation, and chest pain6.
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Disclaimer
The content presented in this blog is generated by Consensus, an AI-powered academic search engine, and is based on publicly available scientific literature. While every effort is made to provide accurate, up-to-date, and well-researched information, the content is intended for informational and educational purposes only. It does not constitute medical advice, diagnosis, or treatment. Always consult a qualified healthcare professional before making any decisions regarding medical conditions, treatments, or medications. The AI system’s analysis may not cover all perspectives, emerging research, or individual cases, and it is not a substitute for professional expertise. Neither the blog publisher nor the developers of the AI-powered search engine are responsible for any actions taken based on the information provided in this content. Use of this information is at your own risk. Citations to the original scientific studies are included for reference, but these studies should be reviewed in full and interpreted with the guidance of a healthcare or research professional.
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