Ingredient guide
Vitamin B12, or cobalamin, is an essential vitamin for nerves, blood cells, and DNA. The strong evidence is for correcting a shortfall, which is common in older adults, vegans, and people with absorption problems. Extra B12 does little for people who already have enough.
High-quality evidenceVitamin B12, also called cobalamin, is an essential water-soluble vitamin. Essential means your body cannot make it, so it has to come from food. It is found almost only in animal foods such as meat, fish, eggs, and dairy, plus fortified products. That food pattern is why the supplement matters so much for some groups.
B12 is a cofactor for two important reactions. One keeps the protective coating around your nerves healthy, and the other supports the production of red blood cells and DNA. Absorbing it is unusually complex. It needs stomach acid and a protein called intrinsic factor, which is why absorption problems are a common cause of a shortfall.
The core evidence is strong and simple. A true B12 shortfall causes real harm, including a type of anaemia and nerve symptoms that can become lasting if ignored, and correcting it resolves these. Deficiency is common in older adults, in vegans and vegetarians, and in people whose guts cannot absorb it well.
Research also shows that high-dose oral B12 works for many people, even some with absorption problems, because a small amount is absorbed without intrinsic factor. Injections remain useful for severe cases. We grade the evidence as high for correcting a shortfall. For people who already have enough, though, extra B12 brings little benefit.
Most people who eat animal foods get enough B12. Vegans, vegetarians, people over 50, and those on metformin or long-term acid reducers are the groups most likely to need a supplement, often 50 mcg to 1,000 mcg a day. If you have nerve symptoms or marked fatigue, see a healthcare provider, since a proper diagnosis guides whether you need tablets or injections.
The adult recommended intake is about 2.4 mcg per day, easily met by animal foods. Supplements often supply far more, from 50 mcg to 1,000 mcg, because only a small fraction is absorbed. There is no upper limit, as excess is excreted. Ask your healthcare provider about injections if you have a severe shortfall or absorption problem.
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It is very safe. B12 is water soluble, so excess is passed in urine rather than stored to harmful levels, and there is no set upper limit.
High-dose oral B12 works for many people, even some with absorption problems. Injections are useful for severe shortfalls. A provider can advise which suits you.
Long-term metformin can reduce how well the gut absorbs B12. People on it for years are often advised to have their B12 checked.