Approximate dose-response bands. Individual response varies — these are starting points, not prescriptions.
Pernicious anemia, neurological symptoms, fatigue. Risk is high in vegans, older adults, and metformin users.
Energy and cognitive function may be affected before frank deficiency shows on labs.
DV (2.4 mcg) met. Methylcobalamin and methylfolate together support methylation cycles.
Higher oral doses (500–1000 mcg) commonly used for sub-optimal status — B12 has no UL.
No established harm at high oral doses; excess is renally cleared.
You're at 0% of your vitamin b12 target. The biggest single-serving sources to top it off:
Cobalamin is the largest, most structurally complex vitamin, containing a cobalt ion at the centre of a corrin ring. It cycles between methylcobalamin (methionine synthase) and adenosylcobalamin (methylmalonyl-CoA mutase) and is the cofactor that distinguishes folate's clinical presentation in deficiency. Strict vegans, older adults on PPIs, and gastric bypass patients are the highest-risk groups.
Methionine synthase transfers a methyl group from 5-MTHF to homocysteine, regenerating tetrahydrofolate and producing methionine (precursor to SAMe, the universal methyl donor). When B12 is low, folate is trapped as 5-MTHF and DNA synthesis stalls (megaloblastic anemia). Methylmalonyl-CoA accumulates when adenosylcobalamin is deficient, disrupting myelin lipid synthesis — explaining the neurological signs.
Common in older adults (atrophic gastritis impairs absorption), PPI/metformin users, vegans, and post-bariatric patients. Frequently missed because folate fortification corrects the haematological picture while neurological damage progresses.
No UL; B12 is excreted readily and toxicity has not been reported. Some observational data suggest very high serum B12 in non-supplementing adults may flag underlying liver or hematologic disease.
Methylcobalamin and adenosylcobalamin are the two coenzyme forms. Hydroxocobalamin has the longest serum half-life. Cyanocobalamin works for most healthy people but requires conversion and is usually penalized by Formulate's scoring. Sublingual or oral high-dose (1,000+ mcg) supplements work for most absorption deficits because passive uptake bypasses intrinsic factor.
Two absorption routes: a saturable intrinsic-factor-dependent route in the terminal ileum (absorbs ~1–2 mcg per meal) and an unregulated passive route that absorbs ~1% of any dose. High-dose oral B12 (1,000+ mcg) exploits the passive route and matches injections for most deficiencies — except true pernicious anemia, where IM is more reliable.
Adequacy is non-negotiable for cognitive and neurological healthspan, especially after age 50. The neurological damage from prolonged deficiency is partially or fully irreversible — early correction matters. No evidence that megadosing past adequacy adds benefit.
Myelin synthesis, red blood cell production, methylation cycle.
Forms with lower absorption: cyanocobalamin. Prefer better-absorbed forms when supplementing.
The mechanisms and systems this nutrient feeds. Click any to drill into what runs on it.
★ = load-bearing / primary cofactor. Track these in My Journey.
Whole foods that contribute meaningfully (≥10% DV per 100 g serving). Click any food to see its full nutrient profile and what else it brings to the table.
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