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

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

score

evidence

Safe

risk

Proven Benefits

01Corrects B12 deficiency

02Reverses megaloblastic anemia

03Lowers homocysteine

04Improves neuropathy if low

05Improves fatigue when deficient

06May improve cognition if low

Chemical Forms

Recommended

Cyanocobalamin
Methylcobalamin
Hydroxocobalamin

Avoid

Spirulina/algae 'B12' analogs (often inactive corrinoids)
Adenosylcobalamin-only products (less evidence as a sole form)

Expert Note

Cyanocobalamin is the most studied, stable, and inexpensive oral form. Methylcobalamin also works, but it is not clearly superior for most users, and sublingual tablets are not proven better than regular tablets when the dose is adequate. Products sold as algae or spirulina B12 may contain inactive corrinoid analogs and are unreliable as a sole source.

Protocol

Amount

250-500 mcg

Frequency

Once daily

When

Any time of day — consistency matters more than timing; with or without food.

Condition-Based Dosing

Vegan or strict vegetarian adults

250-500 mcg daily or 1000 mcg 2-3 times per week— Plant foods do not reliably provide active B12 unless fortified.

Adults over 60

500-1000 mcg daily— Food-bound B12 absorption often falls with age, even when intake looks adequate.

Metformin or long-term PPI/H2 blocker use

500-1000 mcg daily— These medicines can reduce B12 absorption over time; periodic labs are reasonable.

Serum B12 borderline low or MMA elevated

1000 mcg daily for 8-12 weeks, then retest— High-dose oral B12 works for many people because a small fraction is absorbed passively.

Confirmed deficiency without severe neurologic symptoms

1000-2000 mcg daily under clinician guidance— Injections may be preferred if malabsorption or pernicious anemia is suspected.

Safety & Limits

Upper Safe Limit

No official UL for adults (IOM/NASEM); oral doses up to 1000-2000 mcg/day are commonly used in practice.

Cycling

Safe for continuous use

Contraindications

Leber hereditary optic neuropathy — avoid cyanocobalamin unless a clinician advises otherwise

Cobalt allergy — rare hypersensitivity reactions are possible

Unexplained anemia or neuropathy — self-treatment can delay diagnosis of pernicious anemia or other causes

Synergies

Folate

B12 and folate work together in one-carbon metabolism and red blood cell DNA synthesis; low folate can limit full correction of macrocytic anemia.

Vitamin B6

B6, folate, and B12 jointly recycle homocysteine, so combined deficiency is common when homocysteine stays high.

Avoid Combining With

✕Metformin (reduces absorption with long-term use)
✕Proton pump inhibitors like omeprazole (reduce release of B12 from food over time)
✕H2 blockers like famotidine (lower stomach acid and food-bound B12 absorption)
✕Nitrous oxide exposure (inactivates B12 and can trigger deficiency symptoms)
✕Heavy alcohol use (can impair absorption and worsen deficiency)

Updated Invalid Date