Vitamin B12
Vitamin B12, or cobalamin, is an essential water-soluble vitamin made by bacteria and found almost only in animal foods.
Also listed as Cyanocobalamin, cobalamin, methylcobalamin, 5-deoxyadenosylcobalamin
What it is studied for
The strongest rated effects first. Bars show the size of the effect, the letter grades the evidence, and each rating lists the studies behind it.
What does B12 do?
Vitamin B12 supports red blood cell formation, DNA synthesis and the development and function of the nervous system. These essential functions explain why deficiency matters; they do not establish that extra B12 improves every function in someone already adequately supplied. 1 2
Enough in your food does not always mean enough in your body
The body must release B12 from food proteins, bind it to a stomach protein called intrinsic factor and absorb it in the intestine. Problems along that route can cause deficiency even when intake looks adequate. Older adults, people with certain gastrointestinal conditions or surgery, and people taking metformin or acid-suppressing medicines deserve particular attention. 1
A vegan diet needs a dependable B12 supplement, according to DGE. The body stores enough B12 for deficiency symptoms to take years to appear, so feeling well today does not establish that a diet is supplying enough. 1 3
Key studies
The most recent publications linked to Vitamin B12's ratings.
Why people take it
SuppCo community snapshot, 2026-09-28. Reasons for use are not evidence that it works.
Questions people ask
Can I be deficient without anemia?
Yes. Neurological symptoms of B12 deficiency can occur without anemia, so a normal blood count does not exclude the problem. 1
Does a vegan diet need a supplement?
DGE recommends B12 supplementation with a vegan diet. Symptoms may take years to appear because the body stores B12. 1 3
Is methylcobalamin better absorbed?
NIH reports no evidence of different absorption rates between supplement forms. The form name alone is not a reliable reason to expect a better result. 1
Are injections always better than tablets?
Small trials found that high-dose oral B12 could restore blood levels, but did not report clinical symptom outcomes. The cause and severity of deficiency matter when choosing a route. 1 4
Will B12 help tiredness if my level is normal?
Research on unexplained fatigue without overt deficiency was too limited for a pooled conclusion in the 2021 review. A benefit cannot be reliably predicted from those studies. 5
Can I rely on one borderline blood result?
A borderline serum B12 result may need an MMA test and clinical assessment. Kidney function can affect MMA, so the tests need to be interpreted together. 1
Related nutrients
Vitamin B3
Vitamin B1
Vitamin B Complex
Vitamin B6Sources
- Vitamin B12: Fact Sheet for Health Professionals NIH Office of Dietary Supplements
