Vitamin B12 (Cobalamin)

VitaminFoundational

Protects your nerves and builds red blood cells. Deficiency damage can be permanent.

At a glance

Essential · test if at risk

Protects nerves Needed to build myelin, the insulation around nerves. why ↓
Builds red blood cells Without it, cells come out large and dysfunctional. why ↓
Keeps homocysteine down Recycles homocysteine back into methionine. why ↓

Strong human evidence

How to take it

About 2.4 mcg a day
Clams, liver, salmon, beef, dairy, eggs

Watch out

Higher risk if vegan, older, on metformin, or after stomach surgery
Very low toxicity

Signs you're low

Numbness, tingling, balance problems
Fatigue from anemia
Memory or mood changes

The Research

Mechanisms, studies and evidence grades for each claim above.

Functions

Myelin formation and neurologic function
Red blood cell production
Methylation and energy metabolism

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Mechanism

Two enzyme roles: methionine synthase (converts homocysteine back to methionine — see Methionine and Vitamin B9) and methylmalonyl-CoA mutase (converts to succinyl-CoA, feeding the TCA cycle).

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Intake / absorption

RDA roughly 2.4 mcg/day for adults. Comes from animal or fortified foods; absorption requires intrinsic factor and an intact ileum, and decreases with age generally. Higher deficiency risk with a vegan diet, pernicious anemia, gastric surgery/disease, or metformin use.

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Deficiency effects

Megaloblastic anemia; neuropathy, numbness/tingling, gait issues, cognitive/mood changes; elevated MMA and homocysteine. Neuropathy and cognitive changes can be irreversible if deficiency goes uncorrected too long.

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Excess effects

Generally low toxicity.

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Top foods

Clams
Liver
Salmon
Tuna
Beef
Milk
Yogurt
Cheese
Eggs
Fortified plant milk
Fortified cereal

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