Deficiency Guide

Vitamin B12 deficiency

Symptoms, at-risk groups, and clinical context for vitamin b12 deficiency. Sourced from NIH Office of Dietary Supplements and StatPearls.

→ See full Vitamin B12 profile

Vitamin B12 deficiency affects roughly 6% of US adults under 60 and ~20% over 60. It's especially common in vegans, the elderly, and long-term users of metformin or proton pump inhibitors. Untreated deficiency can cause irreversible neurological damage, so early detection matters.

Common symptoms

Fatigue, weakness, and shortness of breath (from megaloblastic anemia)
Numbness or tingling in the hands and feet (peripheral neuropathy)
Cognitive issues — brain fog, memory problems, difficulty concentrating
Mood changes — depression, irritability
Sore or swollen tongue (glossitis), mouth ulcers
Pale or jaundiced skin
Balance problems or unsteady gait (in advanced cases)

At-risk groups

Vegans and strict vegetarians (B12 is found almost exclusively in animal foods)
Adults aged 60+ (atrophic gastritis reduces B12 absorption)
Long-term metformin users (>4 years) — metformin reduces B12 absorption by up to 30%
Long-term proton pump inhibitor users (omeprazole, pantoprazole, esomeprazole >1 year)
People with pernicious anemia (autoimmune destruction of intrinsic factor)
Post gastric bypass or ileal resection surgery patients
People with Crohn's disease or celiac disease

When to see a doctorIf you fall into an at-risk group AND experience persistent fatigue plus neurological symptoms (numbness, tingling, balance issues, or memory problems), ask your doctor for a serum B12 test. Methylmalonic acid (MMA) and homocysteine are more sensitive markers when B12 is borderline.

Sources: NIH ODS — Vitamin B12 Health Professional Fact Sheet · PMID 28768707 — Vitamin B12 deficiency review (NEJM)

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Related deficiencies

Nutrients with overlapping symptoms — useful when investigating an unclear clinical picture.

Folate Phosphorus / Phosphate Thiamine Niacin Vitamin C Vitamin B6 (Pyridoxine)