The signs below come from NIH Office of Dietary Supplements and the NHS. None of them confirms deficiency on its own — several have common unrelated causes — but together they are the documented picture.
The documented signs
- Fatigue. Listed by NIH ODS, and the least specific item here.
- Megaloblastic anemia. Abnormally large red blood cells, detectable on a blood count.
- Glossitis of the tongue. A sore, inflamed tongue — one of the more distinctive signs.
- Palpitations. Documented by NIH ODS.
- Pale skin. Reflecting the anemia component.
- Numbness and tingling in hands and feet. The neurological change NIH ODS highlights.
- Low counts of white and red blood cells or platelets.
- Weight loss.
- Mouth ulcers. Named by the NHS.
- Dementia-type changes. NIH ODS lists dementia among effects; it also notes studies have found associations between B12 deficiency and depression.
The timing problem
NIH ODS states that "the symptoms of vitamin B12 deficiency can take several years to appear." Deficiency develops slowly enough that people adapt to it, and the gradual onset is part of why it goes unnoticed.
The sign that changes urgency
The neurological symptoms deserve separate weight. NIH ODS notes they can occur without anemia, and stresses early diagnosis "to avoid irreversible damage." Tingling and numbness are therefore not symptoms to monitor for a few more months.
What to do
If several of these apply — particularly the neurological ones, or if you are in a risk group such as vegans, older adults, or people on metformin or proton pump inhibitors — this warrants a clinical conversation rather than a supplement bought on spec.
Our free B12 symptom check organizes these for that conversation.
References
This article summarizes published guidance from the sources linked above. It is general information, not medical advice, and it cannot tell you whether you personally have a deficiency. Only a clinician ordering the right test can do that. If you have symptoms that concern you, speak to a doctor.