Vitamin B12 Deficiency: Why It Causes Brain and Nerve Damage — and Who Is at Risk in India

Vitamin B12 deficiency is one of the most common and most underdiagnosed conditions in Indian neurology practice. Studies suggest that 47–73% of vegetarians in India are B12 deficient — and the neurological consequences of prolonged deficiency are severe and sometimes irreversible if not treated promptly.

Why Indians Are Particularly at Risk

Vitamin B12 is found almost exclusively in animal products: meat, fish, eggs, and dairy. While dairy products do contain some B12, the amounts are modest, and many Indians do not consume dairy in quantities sufficient to meet B12 requirements. Strict vegetarians (no dairy or eggs) are at very high risk of deficiency over years.

Additional risk groups: elderly adults (decreased gastric acid reduces B12 absorption); patients taking metformin (for diabetes — metformin reduces intestinal B12 absorption); patients on long-term proton pump inhibitors (PPIs); those with autoimmune gastritis (pernicious anaemia); and people with inflammatory bowel disease.

Neurological Consequences of B12 Deficiency

Subacute combined degeneration of the spinal cord: B12 deficiency causes demyelination of the posterior and lateral columns of the spinal cord — producing a characteristic syndrome: tingling and numbness starting in the feet (stocking distribution), followed by loss of vibration and position sense (proprioception), then spastic weakness in the legs, and in severe cases, incontinence. This is an emergency — the spinal cord damage can become permanent if not treated promptly.

Peripheral neuropathy: Symmetrical "stocking-and-glove" numbness and tingling in the hands and feet — easily confused with diabetic neuropathy. B12 deficiency neuropathy is reversible with treatment; diabetic neuropathy is less so.

Cognitive decline and dementia: B12 deficiency causes measurably reduced cognitive function — memory difficulties, slowed processing, and in severe cases, dementia-like presentation. This is fully reversible in early stages.

Psychiatric symptoms: Depression, irritability, psychosis, and personality change — all reported in B12 deficiency, sometimes without prominent neurological symptoms.

Megaloblastic anaemia: The classic blood finding — large, abnormally shaped red blood cells. However, many patients have neurological symptoms before anaemia develops, so anaemia cannot be used as a screen for neurological risk.

Treatment

Intramuscular B12 injections (cyanocobalamin 1000 mcg) are the most reliable treatment — bypassing the absorption problem in the gut. High-dose oral B12 (1000–2000 mcg daily) is also effective for non-absorption-related deficiency. Treatment should be started promptly whenever B12 deficiency is confirmed and neurological features are present.

For B12 deficiency evaluation and neuropathy assessment: Sri Anand CNC, Chanda Nagar, Hyderabad. Call +91 90633 66983.