Everything You Need to Know About Vitamin B12

Vitamin B12 does a great deal for your body, and it is one of the easiest nutrients to fall short on — particularly on a vegan or vegetarian diet, or as you get older. Here is what it does, where to get it, and how to recognise a deficiency.

What is vitamin B12?

Vitamin B12 (cobalamin) is a water-soluble vitamin. Unlike most water-soluble vitamins, however, the liver can store several years' worth — which is why deficiency often develops slowly and goes unnoticed for a long time.

It is essential for:

• Forming healthy red blood cells
• Maintaining the myelin sheath that protects your nerves
• DNA synthesis
• Normal brain and nervous system function
• Converting food into usable energy

How much do you need?

The UK reference nutrient intake is around 1.5 mcg a day for adults. Requirements rise in pregnancy and breastfeeding. Older adults often need more than the baseline because absorption declines with age.

Which foods contain it?

B12 occurs naturally only in animal-derived foods:

• Meat, particularly liver and kidney
• Fish and shellfish — salmon, mackerel, sardines, clams
• Eggs
• Milk, cheese and yoghurt

For vegans, fortified foods are essential: fortified plant milks, fortified breakfast cereals, and nutritional yeast with added B12. Check labels, as fortification is not universal. Seaweed, spirulina and fermented foods are not reliable sources — they often contain inactive analogues that do not work in the body and can even interfere with testing.

The Vegan Society and NHS both advise that anyone following a fully plant-based diet should take a B12 supplement or use fortified foods consistently.

Why absorption matters as much as intake

B12 absorption is unusually complicated. It requires stomach acid to release B12 from food, and a protein called intrinsic factor, produced in the stomach, to carry it across the gut wall. Anything interfering with either step causes deficiency regardless of how much you eat.

Common causes of poor absorption:

• Pernicious anaemia — an autoimmune condition destroying the cells that make intrinsic factor. This is the most common cause of B12 deficiency in the UK and requires lifelong injections, not tablets.
• Age — stomach acid production declines
• Medications — long-term proton pump inhibitors (omeprazole, lansoprazole) and metformin
• Gut conditions — coeliac disease, Crohn's disease
• Gastric or bowel surgery
• Heavy alcohol use

Symptoms of deficiency

Early signs are easily dismissed: fatigue, weakness, breathlessness, pale or slightly yellow skin, mouth ulcers and a sore, red tongue. As it progresses, neurological symptoms appear — pins and needles in the hands and feet, numbness, unsteadiness, muscle weakness, memory and concentration problems, irritability and low mood.

This is the part that matters most: neurological damage from prolonged B12 deficiency can become permanent if left untreated. Do not wait it out. If you have persistent tingling, numbness or balance problems, see your GP.

Folate can hide it

High-dose folic acid corrects the anaemia caused by B12 deficiency while allowing the nerve damage to continue silently. This is why B12 should always be checked alongside folate before starting high-dose folic acid supplementation.

The genetic angle

Genes including FUT2 and TCN1 influence how efficiently your body transports and uses B12, meaning two people with identical diets can have different blood levels. This can explain persistently borderline results despite reasonable intake — though diet and absorption remain the dominant factors for most people.

Testing with Rightangled

Rightangled's home blood tests can measure B12 alongside folate and a full blood count, processed by accredited UK laboratories. Our DNA tests assess related genetic markers. All results are reviewed by our clinical team, which includes GPhC-registered independent prescribers, with medical oversight from our doctor, Dr Abdullah.

Verify us with the General Pharmaceutical Council (registration 9011933), see our LegitScript certification, and read reviews on Trustpilot.

Related reading: folate deficiency.

This article is for general information and does not replace personalised medical advice. If you have symptoms of B12 deficiency, particularly neurological ones, see your GP.