Vitamin B12 deficiency: 9 symptoms doctors miss too often

B12 deficiency develops slowly – over two to five years. Symptoms are vague and are commonly blamed on stress, age or depression. Here are nine signs that should trigger a B12 check.

9 classic B12 deficiency symptoms

• Chronic fatigue that doesn’t lift with rest
• Tingling or numbness in fingers and toes
• Memory and concentration problems (“brain fog”)
• Pale, slightly yellowish skin
• Red, sore “glossitis” tongue
• Nausea, appetite loss, weight loss
• Depression, irritability
• Reduced tendon reflexes
• Balance problems, unsteady gait – late-stage sign

High-risk groups

• Vegans and strict vegetarians without supplementation
• Over 60 (declining stomach acid, reduced absorption)
• Long-term PPI users (omeprazole, esomeprazole)
• Metformin users (10–30% reduction in absorption)
• Gastritis, coeliac, Crohn’s, partial gastric resection
• Autoimmune atrophic gastritis (pernicious anaemia)

Which tests

Serum B12 alone is insufficient – it mostly shows the biologically inactive fraction. Clinically: serum B12, holotranscobalamin (active B12), homocysteine, methylmalonic acid (MMA). A serum B12 of 200–300 pg/mL with elevated MMA means real deficiency despite “normal” B12.

How to restore

Correcting a deficiency depends on its depth and cause. Milder deficiency is usually addressed with oral cobalamin, while severe deficiency or neurological symptoms are typically treated with injections. The form, dose and duration are decided by a doctor based on tests and the clinical picture – this article is educational and does not replace a consultation.