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Vitamin B12 (Methylcobalamin)
Drives nerve myelination, red blood cell formation, and DNA synthesis — deficiency is common in vegans, vegetarians, and older adults.
What the evidence says
Vitamin B12 appears to help in 4 of 5 studies with measurable effects — the evidence leans clearly favourable.
Most evidence is from high-quality meta-analyses and randomised trials published 1966–2026 with a typical study size of 2,256 participants.
Based on 324 studies · 41 meta-analyses · 226 RCTs · 303,822 total participants
Confidence
High confidenceWhat the studies found
By outcome
Scores Strong because B12 is an essential vitamin with abundant meta-analytic evidence for correcting common deficiency, supporting neurological and red-blood-cell function; benefits in replete people are modest and largely deficiency-driven.
105 trials ongoing or recruiting · 430 completed on ClinicalTrials.gov
73 of the completed trials have posted results
Registered trials show research momentum for Vitamin B12, not proof of effect — a registration is a plan, and posted results are sponsor-reported, not peer-reviewed. They are never counted toward the evidence rating above.
Browse these trials on ClinicalTrials.govClinicalTrials.gov · as of Oct 2026
Under EU law (Reg. 1924/2006), EFSA reviews whether a specific health claim for Vitamin B12 meets the evidence standard. These are independent regulatory decisions on claims — not studies, and never counted toward the evidence score above.
Authorised claims
“Vitamin B12 contributes to normal energy- yielding metabolism”
“Vitamin B12 contributes to normal functioning of the nervous system”
“Vitamin B12 contributes to normal homocysteine metabolism”
“Vitamin B12 contributes to normal psychological function”
“Vitamin B12 contributes to normal red blood cell formation”
“Vitamin B12 contributes to the normal function of the immune system”
“Vitamin B12 contributes to the reduction of tiredness and fatigue”
“Vitamin B12 has a role in the process of cell division”
Not authorised by EFSA
“Vitamin B12 Necessary to maintain energy and general vitality”
“Vitamin B12 Necessary for healthy teeth, bones, hair, skin and nails”
“Not authorised” means the specific claim wording did not meet the EU’s evidence standard — often a matter of dossier or phrasing, not proof of no effect. EFSA judges marketing claims and is kept separate from our study-based evidence score.
Source: EU Register of nutrition and health claims (European Commission / EFSA) · register snapshot Feb 2013
Vitamin B12 is an essential water-soluble vitamin that plays critical roles in neurological function, DNA synthesis, and red blood cell formation. Deficiency is common, especially in vegetarians/vegans, older adults, and those with absorption issues.
Methylcobalamin is the active, neurologically-preferred form, while cyanocobalamin is cheaper but requires conversion.
Essential cofactor for methionine synthase
Supports nerve sheath integrity
Required for healthy red blood cell formation
How Vitamin B12 works — from molecular targets to health outcomes. Click an edge to see supporting research.This visualization is in beta — pathways are being refined and expanded.
Essential to supplement; B12 only found in animal products
Higher doses often needed due to reduced absorption
Metformin can reduce vitamin B12 levels. Ask your clinician about testing if you have symptoms of deficiency and periodic monitoring if you have risk factors. Treat confirmed deficiency according to the agreed plan and continue metformin as prescribed. This is a nutrient-assessment note, not a graded interaction. It does not mean that taking the two together is harmful, or that it has been assessed as safe.
Prolonged acid suppression may contribute to B12 deficiency in some people. Ask whether assessment is appropriate. This is not a warning that taking B12 with these medicines is harmful. This is a nutrient-assessment note, not a graded interaction. It does not mean that taking the two together is harmful, or that it has been assessed as safe.
Tip: Take with food
Tip: Reduce dose if persistent
Tip: Discontinue if symptoms occur
Vitamin B12 has an evidence score of 7.5/10 — strong evidence based on 325 indexed studies, including 17 meta-analyses. Drives nerve myelination, red blood cell formation, and DNA synthesis — deficiency is common in vegans, vegetarians, and older adults. Representative study: PMID 38231320.
The commonly studied dose of Vitamin B12 is 500-1000mcg daily for maintenance; higher for deficiency. Individual needs vary — start at the lower end of the range and adjust based on how you respond.
The best time to take Vitamin B12 is in the morning. Taking it with food is preferred. Vitamin B12 (cobalamin) is essential for methylation (methionine synthase), mitochondrial energy production (methylmalonyl-CoA mutase), and myelin synthesis.
Vitamin B12 is generally well-tolerated and considered safe for most healthy adults at recommended doses. Reported side effects are uncommon and include mild GI upset, acne-like skin eruption (high doses), allergic reaction (rare, usually with injection). Use caution if any of these apply to you: Leber's hereditary optic neuropathy (may worsen); Cobalt or cobalamin hypersensitivity.
Multivitamin
Too few graded studiesNutritional insurance that fills micronutrient gaps. In the large COSMOS trial, a daily multivitamin improved memory and slowed cognitive decline in older adults — but it did not reduce total cancer, cardiovascular disease, or mortality.
Vitamin D3
Probably helpsHormone-like vitamin that regulates 1,000+ genes — deficiency is widespread and linked to poor immunity, depression, and bone loss.
Methylfolate
Likely helpsBioactive folate that bypasses MTHFR conversion — critical for the 30-40% of people with gene variants affecting mood and methylation.
B-Complex
Probably helpsEssential B vitamins in their active methylated forms, supporting energy production, mood, and cognitive function.
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Reviewed by Dr. Baher Al Hakim · Last reviewed May 2026 · evidence from 328 studies · how we score · editorial policy
This information is for educational purposes only. It is not a substitute for professional medical advice. Always consult a qualified healthcare provider before starting, stopping, or changing any supplement or medication.
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