Vitamin B12 Deficiency: Signs and Symptoms
Vitamin B12 deficiency presents with a broad spectrum of hematologic, neurologic, cognitive, and visual manifestations that can occur with or without anemia, making clinical recognition essential for preventing irreversible neurological damage. 1
Hematologic Manifestations
- Macrocytic anemia (elevated MCV on blood count)
- Macrocytosis without anemia (can occur in early deficiency)
- Abnormal blood count findings
- Iron-refractory anemia during pregnancy/breastfeeding 1
Critical pitfall: Many patients present with neurologic symptoms WITHOUT anemia or macrocytosis, particularly in early deficiency—do not wait for hematologic changes to suspect B12 deficiency 2, 3.
Neurologic Manifestations
Peripheral Neuropathy
- Pins and needles or numbness (paresthesia)—often the earliest neurologic symptom
- Tingling sensations in extremities
- Can present as cervical radiculopathy mimicking structural spine disease 4
Central Nervous System (Myelopathy/Spinal Cord Disease)
- Balance issues and falls from impaired proprioception
- Sensory ataxia (may indicate spinal cord damage)
- Impaired gait
- Hand tremor
- Hypotonia (particularly in children) 1, 2
Visual/Optic Nerve Dysfunction
- Blurred vision
- Optic atrophy
- Visual field loss (scotoma) 1
Cognitive and Psychiatric Symptoms
- "Brain fog"—difficulty concentrating and short-term memory loss
- Fatigue (often unexplained and persistent)
- Concentration difficulty
- Can mimic or contribute to delirium or dementia 1, 2
Other Physical Signs
High-Risk Populations Requiring Heightened Suspicion
Dietary Risk Factors
- Vegans/vegetarians without B12 supplementation
- Religious dietary restrictions excluding animal products
- Food allergies (eggs, milk, fish)
- Eating disorders or restricted diets
- Low income/difficulty accessing B12-rich foods 1
Medical Conditions
- Atrophic gastritis (gastric body involvement)
- Autoimmune conditions: celiac disease, type 1 diabetes, thyroid disease, Sjögren syndrome
- Malabsorptive disorders
- H. pylori infection 1, 5
Medication-Induced
- Metformin (most common)
- Proton pump inhibitors and H2 receptor antagonists
- Colchicine
- Phenobarbital, primidone, pregabalin 1, 6
Age-Related
- Older adults (prevalence 2-3% in US adults, higher with age) 6
Clinical Approach Algorithm
When to suspect B12 deficiency:
- Any patient with ≥1 risk factor PLUS ≥1 clinical feature above 6
- Unexplained neurologic symptoms even without anemia 2, 3
- Macrocytosis on routine blood work
- Cognitive decline in at-risk populations
Critical warning: Neurological damage from B12 deficiency can become irreversible if diagnosis and treatment are delayed 4, 3. The severity of long-term neurologic impairment correlates with duration of untreated deficiency, making early recognition paramount for preserving quality of life and preventing permanent disability.
Special pediatric consideration: In infants 2-12 months, look for developmental regression, hypotonia, failure to thrive, abnormal movements (tremors, myoclonus), and lethargy—often from exclusively breastfed infants of deficient mothers 7, 2.