Vitamin B12
Methylcobalamin
also known as Methylcobalamin, Cobalamin, Cobalamins, Cyanocobalamin
A B vitamin made only by bacteria — animals get it by eating contaminated food, dairy, or other animals; plants don't make it at all. Vitamin B12 is essential for red blood cell formation, nerve function, and DNA synthesis. Deficiency is common in older adults, vegans, and people on certain medications, and untreated B12 deficiency causes nerve damage that can become permanent.
- Essential for red blood cell formation — deficiency causes a specific type of anemia (megaloblastic)
- Required for nerve health and the maintenance of the myelin sheath that insulates nerves
- Required for DNA synthesis and cell division
- Works closely with folate — deficiency in either creates similar blood symptoms but only B12 deficiency causes nerve damage
- Methylcobalamin and adenosylcobalamin are the active forms; cyanocobalamin (cheaper supplement form) converts to active forms in the body
- Found in animal foods — meat, fish, poultry, eggs, dairy. Vegans need fortified foods or supplements
- Sublingual and injection forms bypass absorption issues common in older adults and people with stomach conditions
Absorption requires intrinsic factor, made by the stomach — pernicious anemia, atrophic gastritis, and gastric bypass surgery all impair absorption
Long-term use of metformin, proton pump inhibitors (omeprazole, etc.), and H2 blockers reduces B12 absorption
About 10-15% of adults over 60 have low B12 levels — testing is worthwhile, especially with neurological symptoms
Vegans and strict vegetarians need supplementation — there is no reliable plant source of active B12 (claims about spirulina, fermented foods, etc. don't hold up)
Untreated B12 deficiency causes irreversible nerve damage — early treatment matters
Folate supplementation can mask the blood signs of B12 deficiency while nerve damage progresses — testing both matters
Generally very safe in supplemental form; excess is excreted
Some people with MTHFR or related genetic variants do better with methylcobalamin than cyanocobalamin
Research
- Comment on: "Clinical safety of ultra-high-dose methylcobalamin in patients with amyotrophic lateral sclerosis: Open-label extension of a phase 2/3 randomized controlled study".
- Ultra-high-dose methylcobalamin demonstrates safety in advanced ALS, but intramuscular administration poses practical burdens and its selected study cohort limits generalizability.
- Response to letter to the editor "Comment on: Clinical safety of ultra-high-dose methylcobalamin in patients with amyotrophic lateral sclerosis: Open-label extension of a phase 2/3 randomized controlled study".
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