Vitamin B12 deficiency is one of the most commonly missed nutritional deficiencies in the UK — partly because it develops slowly, partly because its symptoms are non-specific and mimic many other conditions, and partly because testing isn’t routine. Left untreated, it can cause irreversible neurological damage. Understanding who is at risk and when to act is important.
Why B12 Is Essential
Vitamin B12 (cobalamin) is essential for: myelin synthesis — the protective sheath around nerve fibres (B12 deficiency causes demyelination, producing neurological symptoms); DNA synthesis and red blood cell formation (deficiency causes megaloblastic anaemia); and — working with folate — reducing homocysteine (elevated homocysteine is an independent risk factor for cardiovascular disease, stroke and dementia).
Who Is at Risk
Vegans and strict vegetarians — B12 is found exclusively in animal products (meat, fish, eggs, dairy). Vegans must supplement. The UK Vegan Society recommends either a reliable daily supplement (10mcg or more) or a higher-dose twice-weekly supplement (2000mcg). Older adults (over 50) — gastric acid production declines with age, and B12 from food requires gastric acid for release from food proteins. Food-B12 absorption decreases significantly; supplement B12 (which doesn’t require gastric acid) is better absorbed. People taking metformin — metformin reduces B12 absorption through its effect on ileal B12 transport; long-term use (>4 years) is associated with significant B12 depletion. Annual B12 testing is recommended in people on long-term metformin. People taking PPIs or H2 blockers — reduce gastric acid and impair food-B12 absorption. Pernicious anaemia — autoimmune destruction of gastric parietal cells, preventing production of intrinsic factor essential for B12 absorption. Requires intramuscular B12 injections (bypassing the absorption deficit). Ileal disease or resection — B12 is absorbed in the terminal ileum; Crohn’s, ileal surgery and coeliac disease impair absorption.
Symptoms of B12 Deficiency
Haematological: fatigue, pallor, macrocytic anaemia. Neurological (can occur without anaemia): peripheral neuropathy (tingling, numbness, burning in feet/hands), subacute combined degeneration of the cord (weakness, balance problems, spasticity — requires urgent treatment); depression, cognitive impairment, memory difficulties. Oral: glossitis (beefy red, smooth tongue), mouth ulcers. The neurological damage can be irreversible — early detection and treatment is crucial.
Testing and Treatment
Serum B12 testing via GP. Levels: above 300 ng/L — adequate; 200–300 ng/L — borderline (retest in 3–6 months or supplement); below 200 ng/L — deficient (treat). For dietary deficiency: oral B12 supplementation (1000mcg daily) is effective even for some absorption disorders, as passive absorption (not requiring intrinsic factor) functions at high doses. For pernicious anaemia: intramuscular hydroxocobalamin injections (every 3 months maintenance).
Frequently Asked Questions About B12
Do B12 supplements give you energy?
B12 supplementation improves energy in people who are deficient — correcting the fatigue and cognitive effects of deficiency. In people with adequate B12, additional supplementation does not boost energy or cognitive function above baseline. The energy boosts marketed for high-dose B12 injections in non-deficient people are primarily placebo effect.
Can sublingual B12 replace injections?
For dietary B12 deficiency, high-dose oral or sublingual B12 (1000mcg daily) is as effective as intramuscular injections in most cases. For pernicious anaemia with confirmed intrinsic factor deficiency, injections remain the standard because intramuscular delivery bypasses the absorption deficit completely. Some patients with PA are successfully managed on very high-dose oral B12 (1000–2000mcg daily) through passive absorption.
Browse B12 supplements at Huncoat Pharmacy including sublingual formulations. Related: Vegan Nutrition, Iron Deficiency.
At Huncoat Pharmacy: Vitamin B12 injection & IV infusion service, Browse B12 supplements, B12 deficiency home testing kit.