Signs you may have vitamin B12 deficiency: A clinical guide to symptoms and testing

Signs you may have vitamin B12 deficiency can be subtle at first, with persistent fatigue, weakness, tingling, balance changes, or memory problems developing gradually. Symptoms alone cannot establish the diagnosis, because several other conditions can produce similar complaints, but recognizing the pattern can help determine when clinical assessment and blood testing are appropriate. 1

Early symptoms linked to anemia

Vitamin B12 is required for the formation and maturation of red blood cells. When deficiency interferes with that process, anemia may develop and reduce oxygen delivery to tissues. Common symptoms include unusual tiredness, weakness, lightheadedness, pale skin, shortness of breath, and heart palpitations. Some people may also feel dizzy or notice reduced exercise tolerance. These findings are not specific to B12 deficiency, but their persistence is a reason to discuss possible anemia with a healthcare professional. 2

Fatigue may appear before more distinctive symptoms and can be overlooked when it is attributed to poor sleep, stress, or routine demands. B12 deficiency can also occur without obvious anemia, meaning a normal blood count does not always exclude a problem involving nerve function. A clinical assessment generally considers the full symptom pattern, diet, medical history, medications, and laboratory results rather than relying on tiredness alone. 3

Numbness, tingling, and balance changes

Neurological symptoms are among the more important signs to recognize. Vitamin B12 deficiency may affect peripheral nerves, producing numbness, pins and needles, tingling, or burning sensations in the hands and feet. Muscle weakness, reduced reflexes, unsteady movement, impaired balance, and difficulty walking can occur when deficiency becomes more severe. These changes may develop gradually, so they can initially be mistaken for circulation problems or ordinary aging. 2

Delayed treatment matters because prolonged nerve injury may not fully resolve, even after B12 levels are corrected. New or worsening numbness, trouble walking, significant weakness, or repeated falls should therefore receive medical evaluation. Those symptoms can also result from neurological disease, diabetes, medication effects, or other causes, so self-diagnosis is unreliable. The clinical priority is identifying the cause while neurological changes are still potentially reversible. 4

Mouth and digestive warning signs

A smooth, swollen, red, or painful tongue, sometimes called glossitis, is a recognized physical manifestation of B12 deficiency. Mouth soreness or oral discomfort may occur alongside changes in appetite. Digestive symptoms can include constipation, diarrhea, nausea, abdominal discomfort, and unintentional weight loss. These problems may be mild or intermittent, and they overlap with many gastrointestinal disorders, so they should be interpreted alongside blood, neurological, and dietary findings. 3

Digestive symptoms may also point toward the underlying reason for low B12 rather than merely being a consequence of it. Conditions affecting the stomach or small intestine can interfere with absorption, including pernicious anemia, chronic stomach inflammation, celiac disease, Crohn’s disease, bacterial overgrowth, or previous gastrointestinal surgery. Identifying the cause is important because dietary changes alone may not correct a problem caused by impaired absorption. 3

Memory, mood, and vision changes

Low B12 can be associated with brain fog, reduced concentration, memory difficulty, confusion, depression, and other changes in thinking or mood. Severe deficiency may produce dementia-like symptoms, although these findings have many possible explanations. Neurological and cognitive effects can occur with or without prominent anemia, which is why mental changes should not be dismissed solely because a person lacks pale skin or severe fatigue. 4

Vision changes have also been reported, particularly in severe or prolonged deficiency involving the optic nerves. New visual symptoms, confusion, or rapidly changing cognition require prompt clinical attention because they may signal conditions unrelated to vitamin B12. A healthcare professional may need to evaluate nutritional status together with neurological, eye, metabolic, medication-related, or psychiatric causes rather than attributing every symptom to a vitamin deficiency. 5

Who faces a higher risk?

Risk is higher when dietary intake is limited or absorption is impaired. Vitamin B12 occurs naturally in animal-derived foods, while fortified foods and supplements can provide alternative sources. People following vegan diets without reliable fortified foods or supplementation may therefore be at risk. Pernicious anemia is another important cause because the body lacks intrinsic factor, a stomach protein needed to absorb B12 in the intestine. 1

Additional risk factors include older age, atrophic gastritis, celiac disease, Crohn’s disease, gastrointestinal surgery, chronic alcohol use, and long-term use of metformin or acid-reducing medicines. Risk does not prove deficiency, and people without an obvious risk factor can still develop it. Conversely, symptoms in a person with several risk factors should not be ignored simply because the symptoms seem nonspecific or developed slowly. 3

How clinicians investigate suspected deficiency

Diagnosis generally begins with a complete blood count and a serum vitamin B12 measurement, interpreted in the context of symptoms and risk factors. The American Academy of Family Physicians reports that a serum level below 180 pg/mL is diagnostic for deficiency, while borderline values from 180 to 350 pg/mL may require methylmalonic acid testing. These thresholds guide evaluation, but laboratory interpretation should remain under clinical supervision. 4

Universal screening is not generally recommended, but testing may be considered when a person has at least one risk factor and one compatible clinical feature. Further investigation may be needed when the cause is unclear, including assessment for atrophic gastritis, Helicobacter pylori, or autoimmune antibodies. Treatment depends on the cause and severity and may involve oral B12, dietary measures, or injections when absorption is impaired. 4

Sources

1. Harvard Health Publishing, Vitamin B12 Deficiency: https://www.health.harvard.edu/preventive-care/vitamin-b12-deficiency-a-to-z
2. MSD Manual Consumer Version, Vitamin B12 Deficiency: https://www.msdmanuals.com/home/disorders-of-nutrition/vitamins/vitamin-b12-deficiency
3. Ohio State Health & Discovery, Is it a vitamin B12 deficiency?: https://health.osu.edu/wellness/exercise-and-nutrition/is-it-a-b12-deficiency
4. American Academy of Family Physicians, Vitamin B12 Deficiency: Common Questions and Answers: https://www.aafp.org/afp/2025/0900/vitamin-b12-deficiency
5. NHS, Vitamin B12 or folate deficiency anaemia symptoms: https://www.nhs.uk/conditions/vitamin-b12-or-folate-deficiency-anaemia/symptoms/