What Is Vitamin B12?
Vitamin B12 (cobalamin) is a water-soluble vitamin essential for red blood cell formation, nerve function, and DNA synthesis. Unlike most water-soluble vitamins, it’s stored in meaningful amounts in the liver — enough to last two to five years in a healthy adult — which is why deficiency tends to build slowly and often goes unnoticed until it’s fairly advanced.
Crucially, B12 is found almost exclusively in animal products. Plant foods don’t naturally contain it, which makes this one of the clearer nutritional gaps to plan around on a vegan or vegetarian diet.
Why Your Body Needs It
EFSA-authorised health claims for vitamin B12 include:
- Contributes to the reduction of tiredness and fatigue
- Contributes to normal energy-yielding metabolism
- Contributes to normal functioning of the nervous system
- Contributes to normal psychological function
- Contributes to normal red blood cell formation
- Contributes to normal homocysteine metabolism
- Has a role in the process of cell division
- Contributes to the normal function of the immune system
Signs of Vitamin B12 Deficiency
Because B12 is stored for years, symptoms often develop gradually over months and can be mistaken for other things:
- Persistent fatigue and low energy
- Pins and needles or numbness (typically hands and feet)
- Pale or slightly yellow-tinged skin
- Sore or inflamed tongue
- Difficulty concentrating, brain fog, memory issues
- Low mood or irritability
- Poor balance or unsteady gait (more advanced cases)
Because many of these overlap with iron deficiency, both are usually checked together via a blood test rather than assumed from symptoms alone.
Who’s Most at Risk
- Vegans and, to a lesser extent, vegetarians — the single biggest dietary risk factor, since B12 isn’t naturally present in plant foods
- Adults over 50 and especially over 75 — stomach acid production declines with age, and acid is needed to release B12 from food
- People with digestive conditions — Crohn’s disease, coeliac disease, or a history of gastric/bowel surgery can impair absorption
- Long-term metformin users — the diabetes medication is known to reduce B12 absorption over time
- People with pernicious anaemia — an autoimmune condition preventing B12 absorption, which requires medical management, not just supplementation
Food Sources
- Meat, particularly liver
- Fish and shellfish (clams and mackerel are especially rich)
- Eggs
- Dairy products
- Fortified foods — some plant milks, nutritional yeast, and breakfast cereals in the UK/EU are fortified with B12, making them a genuinely useful source for vegans
Choosing a B12 Supplement
- Cyanocobalamin is the most common, stable, and affordable form
- Methylcobalamin is the “active” form the body uses directly, often preferred by people wanting a form closer to what’s naturally metabolised
- Sublingual (under-the-tongue) tablets are popular for faster absorption into the bloodstream, bypassing some digestive-tract absorption issues
- Vegans and strict vegetarians should supplement or rely on fortified foods as standard practice, not just when symptoms appear
Our pick: Solgar Methylcobalamin B12 1000mcg — a sublingual, methylated form of B12.
Could low B12 be behind your fatigue?
Take our free 2-minute AI analysis — it looks at your diet, energy levels, and lifestyle together and builds a personalised 30-day plan.
This page is for general educational purposes only and is not medical advice. Persistent numbness, balance issues, or memory changes should be checked by a GP — these can indicate a deficiency that needs medical, not just dietary, correction.
Sources & Further Reading
- NHS — Vitamin B12 or folate deficiency anaemia
- NIH Office of Dietary Supplements — Vitamin B12 Fact Sheet
- EFSA — Health claims on vitamin B12
- Linus Pauling Institute — Vitamin B12 Micronutrient Information
- Examine.com — Vitamin B12
As an Amazon Associate, Nutralyze earns from qualifying purchases. This doesn’t affect our recommendations.