Vitamin B12 Deficiency Symptoms — and How to Fix It

Why B12 Deficiency Is More Common Than You Think

Vitamin B12 is essential for nerve function, red blood cell production, and DNA synthesis — and it's found almost exclusively in animal products: meat, fish, dairy, and eggs. That makes deficiency a near-universal concern for vegans and vegetarians, and a significant issue for older adults who often have reduced stomach acid (necessary to extract B12 from food). UK surveys suggest up to 11% of adults over 65 are deficient, and estimates for vegans range from 52–82% when not supplementing.

Deficiency often develops slowly — B12 stores can last 3–5 years — which means symptoms creep up unnoticed until they're serious.

Symptoms of B12 Deficiency

Neurological

• Tingling or numbness in hands and feet (peripheral neuropathy)
• Brain fog, memory problems, difficulty concentrating
• Balance and coordination problems
• Mood changes — depression, irritability
• In severe cases: psychosis, cognitive decline

Physical

• Fatigue and weakness — often significant
• Pale or jaundiced skin
• Sore, inflamed tongue (glossitis)
• Shortness of breath, heart palpitations (from anaemia)
• Mouth ulcers

Critically, neurological symptoms can occur before anaemia develops — and if left untreated long-term, the nerve damage may be irreversible. This is why early detection and correction matters.

Who's at Risk?

• Vegans and vegetarians — plant foods contain virtually no B12 (except some seaweeds in limited amounts)
• Adults over 50 — stomach acid declines with age, reducing absorption of food-bound B12
• Metformin users — this common diabetes drug impairs B12 absorption
• Long-term PPI users — proton pump inhibitors reduce stomach acid
• People with pernicious anaemia — autoimmune destruction of intrinsic factor (necessary for B12 absorption)
• Those with coeliac disease or Crohn's — impaired GI absorption

How to Test Your B12 Levels

Ask your GP for a serum B12 blood test. The NHS reference range is typically 200–900 pg/mL, but many experts consider anything under 400 pg/mL to be suboptimal for neurological health. If your serum B12 is borderline, methylmalonic acid (MMA) and homocysteine tests are more sensitive markers of functional B12 status — these become elevated when cells are actually B12-deficient, even if serum B12 looks normal.

Best Forms of B12 Supplement

Not all B12 supplements are equal:

• Methylcobalamin — the active, bioavailable form; preferred for nervous system health; no conversion required by the body
• Adenosylcobalamin — another active form; works alongside methylcobalamin
• Cyanocobalamin — cheap and synthetic; must be converted by the body; less ideal but still effective at high doses
• Hydroxocobalamin — used in NHS injections; long-acting

For supplementation, methylcobalamin or a methylcobalamin + adenosylcobalamin combination is best. Look for sublingual tablets or sprays — these bypass the need for intrinsic factor, making them effective even in those with absorption problems.

How Much B12 Do You Need?

The UK NRV (Nutrient Reference Value) is 2.5mcg/day — but this is the minimum to prevent severe deficiency in healthy people with normal absorption. Actual needs for optimal neurological health are debated. Most B12 supplements contain 250–1000mcg — this sounds excessive, but oral absorption of B12 is relatively poor (around 1–3% via passive absorption), so high doses are needed to get meaningful amounts into circulation. For most people supplementing orally, 250–1000mcg of methylcobalamin daily is a sensible range. Those with confirmed deficiency or absorption problems may need weekly high-dose supplements or intramuscular injections from their GP.

Food Sources

• Beef liver — 83mcg per 100g (extremely dense source)
• Clams and mussels — 20–99mcg per 100g
• Salmon — 4.9mcg per 100g
• Eggs — 1.1mcg per 100g
• Dairy — 0.4–1mcg per 100g
• Fortified plant milks and cereals — variable (check label)

Bottom Line

B12 deficiency is common, insidious, and serious if left uncorrected. If you're vegan, vegetarian, over 50, or on metformin, get your levels tested and supplement proactively. Use methylcobalamin sublingually at 500–1000mcg daily. Catching and correcting deficiency early protects neurological function and energy for the long term.