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.

score

evidence

Safe

risk

Our methodology: How we evaluate supplements and turn the underlying research into a single rating.

Read full methodology

Overview

Forms

Safety

Stack

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.

Potential benefits

Corrects B12 deficiency

Reverses megaloblastic anemia

Lowers homocysteine

Improves neuropathy if low

Improves fatigue when deficient

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.

Updated 5/19/2026