howtosupplement
Deficiency/Heart/Cognition

Vitamin B12

Essential vitamin that prevents deficiency, supports nerve and red blood cell health, and matters most for vegans and older adults.

Vitamin B12

Vitamin B12

70
score
A
evidence
Safe
risk
Quick Take

Worth it if you eat little animal food, are over 60, or use metformin or acid blockers; otherwise test before supplementing.

Vitamin B12 is a water-soluble vitamin found mainly in clams, liver, fish, dairy, eggs, and fortified foods. It acts as a cofactor for DNA synthesis, red blood cell formation, and myelin maintenance, and helps recycle homocysteine. Best-supported uses are correcting deficiency, reversing megaloblastic anemia, and lowering homocysteine; neurologic or cognitive benefits appear mostly when low B12 is the cause. Vegans, older adults, and people using metformin or acid-reducing drugs benefit most.

Proven Benefits

01
Corrects B12 deficiency
02
Reverses megaloblastic anemia
03
Lowers homocysteine
04
Improves neuropathy if low
05
Improves fatigue when deficient
06
May improve cognition if low

Protocol

Amount
250-500 mcg
Frequency
Once daily
When
Any time of day — consistency matters more than timing; with or without food.

Onset Time

1-4 weeks for symptoms if low; 4-8 weeks for blood markers

Who Should Consider

Vegans and vegetarians
Adults over 60
Metformin users
Long-term PPI or H2 blocker users
People with low B12 or high MMA
Low animal-food intake

Food Sources

  • Clams (~80-100 mcg per 85 g)
  • Beef liver (~70 mcg per 85 g)
  • Salmon or trout (~2.5-5 mcg per 100 g)
  • Milk or yogurt (~1-1.4 mcg per cup)
  • Eggs (~0.5 mcg each)
  • Fortified plant milk or cereal (~1-6 mcg per serving)

How It Works

B12 is required for methionine synthase and methylmalonyl-CoA mutase. These reactions support DNA synthesis, red blood cell production, and myelin maintenance; when B12 is low, methylmalonic acid and homocysteine rise and neurologic and hematologic function can decline.

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