What are the signs of vitamin B12 deficiency?
Nerve symptoms of B12 deficiency can appear without anaemia, and delay in treatment risks damage that cannot be reversed.
Who is most likely to run low
People who eat no animal products have a higher risk of vitamin B12 deficiency.
What this means for you
B12 is the deficiency where waiting has a cost you cannot take back. Most nutrients forgive a bad stretch. This one damages nerves, and nerve damage caught late does not fully heal.
The early signs are easy to dismiss: tiredness, weakness, a sore or smooth tongue, pins and needles in the hands or feet, unsteadiness in the dark, low mood, trouble finding words. The neurological ones matter most, because they are the ones that can become permanent.
Not for everyone. Nerve symptoms can appear without anaemia, so a normal blood count does not rule B12 out. Delay in treatment risks damage that cannot be reversed. If you have numbness or tingling and you belong to one of the risk groups below, ask for the test rather than waiting to see how it goes.
Who is at risk
People who eat no animal products, because B12 is not naturally present in any plant food at all. Where a cereal, plant drink or nutritional yeast carries it, it was added in the factory. Adults over about 50, where between 3 and 43 per cent of people living in the community have been found deficient. People on long-term metformin, which lowers B12 levels. People on proton pump inhibitors or H2 blockers, which interfere with pulling B12 out of food. And anyone who has had stomach or small bowel surgery.
One useful detail for that last group: B12 in a supplement is absorbed about 50 per cent better than B12 bound into food, because it does not need stomach acid to free it first. That is why a tablet often works when a diet change does not.
The good news at the other end is that too much B12 has no established harm, so no upper limit was set. The asymmetry between the two ends is what makes this worth acting on early.
One interaction is worth naming here, because it changes what a blood count means. Large amounts of folic acid can correct the anaemia of B12 deficiency while the nerve damage continues underneath. Low B12 combined with high folic acid has been associated with roughly two to three times higher risk of cognitive impairment in older adults. If you take a high-dose folic acid supplement and belong to one of the groups above, B12 is worth checking rather than assuming.
Written from the evidence cards and the data on this page, then checked back against the sources. Bioma Learn has no human medical reviewer at this time and we say so rather than invent one. Information, not medical advice. How we verify.
Where to get it from food
- Mussel, blue, cooked — 20.4 µg per 3 oz (850% DV)
- Herring, Atlantic, cooked — 18.8 µg per 1 fillet (783% DV)
- Mackerel, Atlantic, cooked — 16.7 µg per 1 fillet (697% DV)
- Chicken, liver, all classes, cooked — 14.3 µg per 3 oz (597% DV)
- Sardine, Atlantic, canned in oil, drained solids with bone — 13.3 µg per 1 cup, drained (555% DV)
All vitamin B12 sources ranked →
A symptom list is not a diagnosis. Every sign on this page has other causes that are more common than a nutrient deficiency, and the way to know is a blood test rather than a checklist.
Full guide: Vitamin B12: who actually needs to worry, and why the damage can be permanent
Source. These neurological symptoms can occur without anemia, so early diagnosis and intervention is important to avoid irreversible damage.
— NIH Office of Dietary Supplements, Health Professional Fact Sheet: Vitamin B12, checked 2026-09-15. Evidence level E.
Source. Vegans who consume no animal products...have a higher risk of developing vitamin B12 deficiency
— NIH Office of Dietary Supplements, Health Professional Fact Sheet: Vitamin B12, checked 2026-09-15. Evidence level E.