What Is Vitamin B12?
Vitamin B12 (cobalamin) is a water-soluble vitamin essential for DNA synthesis, red blood cell production, nerve function, and the metabolism of homocysteine. It's found almost exclusively in animal products — meat, fish, dairy, and eggs — making it a nutrient that plant-based eaters need to monitor actively.
B12 deficiency develops slowly. The liver stores enough to last two to five years, so deficiency often doesn't produce obvious symptoms until it's been insufficient for a long time.
What B12 Deficiency Affects
Neurological function — B12 is required for the production and maintenance of myelin. Deficiency causes progressive demyelination, producing symptoms from tingling and numbness to cognitive decline and irreversible neurological damage.
Energy and red blood cells — Deficiency leads to megaloblastic anaemia: large, poorly functioning red blood cells that can't carry oxygen effectively.
Homocysteine metabolism — B12 deficiency causes homocysteine to accumulate, elevating cardiovascular and neurological risk.
Mood and cognition — Low B12 is associated with depression, anxiety, and cognitive impairment. In older adults, B12 deficiency is a reversible cause of dementia-like symptoms.
Who Is at Highest Risk
- Vegans and vegetarians
- Adults over 50 — intrinsic factor production declines with age
- People taking metformin
- People with low stomach acid — including PPI users
- Anyone with Crohn's disease, coeliac disease
- Gastric bypass surgery patients
B12 Reference Ranges
Below 148 pmol/L: Deficient. 148–221: Low grey zone. 221–725: Normal. Above 725: Elevated (warrants investigation).
How to Address B12 Deficiency
- Oral supplementation — 500–1,000 µg/day methylcobalamin or cyanocobalamin
- High-dose oral B12 — 1,000–2,000 µg/day for absorption issues
- Intramuscular injections — for severe deficiency
- Dietary sources — liver, clams, sardines, beef, eggs, dairy
Is B12 Tested in a Standard Physical?
Sometimes, particularly for patients at known risk. Stem Health tests B12 and folate in every Core and Horizon Assessment.
