Vitamin B12, also known as cobalamin, is one of the eight B vitamins and an essential water-soluble nutrient. It must come from diet, supplements or prescription medication, since the body can't produce it itself, and it plays a central role in red blood cell formation, nerve health, and DNA synthesis.
What Does B12 Do Inside Your Body?
Vitamin B12 is used by the body to:
- Create red blood cells and immune system cells
- Build myelin, the protective insulating layer around nerve cells
- Metabolise nutrients, including amino acids and essential fatty acids
When B12 occurs naturally in food, it's bound to protein and needs to be released through stomach acid and enzymes before it can be absorbed. In fortified foods and supplements, it's already in free form. Either way, B12 then combines with a substance called intrinsic factor in the stomach, allowing it to be absorbed in the small intestine – intrinsic factor is essential for this process to work.
Why Healthy B12 Levels Matter
Because B12 is involved in such fundamental processes, low levels can genuinely affect health in noticeable ways. Adequate intake supports reduced risk of complications like anaemia, and B12 deficiency anaemia can develop when a lack of the vitamin interferes with healthy red blood cell production, leading to abnormally large, poorly functioning cells instead.
Good B12 levels have also been associated with better health in later life, including reduced risk of certain eye and memory-related issues, though these associations are research-based rather than guaranteed outcomes for any individual.
Symptoms of Vitamin B12 Deficiency
B12 deficiency is characterised by megaloblastic anaemia, fatigue, weakness, constipation, appetite loss and weight loss. Other symptoms can include:
- Numbness and tingling in the hands and feet
- Muscular twinges or prickling sensations
- A painful or sore tongue, and mouth ulcers
- Difficulty maintaining balance
- Vision changes
- Low mood, confusion, or memory difficulties
Many of these symptoms are general and can also result from other health conditions, so B12 deficiency shouldn't be assumed without proper testing. Low B12 levels have also been linked to reduced fertility in women.
Who's at Risk of a Vitamin B12 Deficiency?
- Older adults: reduced stomach acid production with age can increase bacterial overgrowth that competes for available B12, on top of naturally reduced absorption
- People with pernicious anaemia: lack intrinsic factor in the stomach, which is required for B12 absorption
- People with coeliac disease or Crohn's disease: may struggle to absorb adequate B12 from food
- Anyone with lupus or similar autoimmune conditions
- People who've had gastrointestinal surgery: affecting stomach acid production, intrinsic factor, or the part of the small intestine responsible for B12 absorption
- Strict vegetarians and vegans: since B12 occurs naturally only in animal products
- Heavy alcohol consumption and certain medications affecting digestion can also interfere with B12 absorption
Best Food Sources of Vitamin B12
- Clams
- Liver
- Trout
- Salmon
- Tuna
- Haddock
- Beef and lamb
- Milk, yoghurt and cheese
- Eggs
- Chicken
- Fortified nutritional yeast
What Can You Do to Ensure Healthy B12 Levels?
The first step is straightforward: eat plenty of B12-rich foods regularly. For vegetarians and vegans, supplements are the best alternative – cobalamin is found in most popular multivitamins and B-complex products, and standalone B12 supplements are also available for those who want to focus specifically on this nutrient. If you're vegan, our guide to vegan B12 food sources covers plant-based and fortified options in more detail.
Some foods, like bread and breakfast cereals, are routinely fortified with B12 and other vitamins such as folic acid, helping support baseline population health.
Understanding the specific cause of a B12 deficiency matters for treatment too – for some people, dietary changes are enough to restore healthy levels, while others may need supplementation or B12 injections from their GP, particularly if absorption itself (rather than intake) is the underlying issue.
Assessing Your B12 Levels
Testing is a sensible way to know for certain whether you're getting enough B12, rather than guessing. Our vitamin B12 test lets you check your levels at home with a simple finger-prick sample, sent for full laboratory analysis, with results delivered securely online. Once you have your results, you can adjust your diet and supplement use with real confidence, rather than uncertainty.
