Vitamin B12 is an essential nutrient that supports red blood cell formation, DNA synthesis, and nervous system function. Understanding what foods have B12 helps ensure you meet your daily requirements through diet. Animal products such as meat, fish, dairy, and eggs are the richest natural sources, whilst those following plant-based diets must rely on fortified foods or supplements. This article explores the best dietary sources of vitamin B12, recommended intake levels, and signs of deficiency to help you maintain optimal health.

What Is Vitamin B12 and Why Do You Need It?

Vitamin B12, also known as cobalamin, is a water-soluble vitamin that plays essential roles in numerous bodily functions. It is crucial for the formation of red blood cells, DNA synthesis, and the proper functioning of the nervous system. Unlike many other vitamins, B12 contains the mineral cobalt, which gives it its alternative name.

The body requires vitamin B12 to maintain healthy nerve cells and to produce the genetic material in all cells. It works closely with folate (vitamin B9) in the synthesis of DNA and red blood cells. Without adequate B12, the body cannot produce enough healthy red blood cells, leading to a condition called megaloblastic anaemia, where red blood cells are larger than normal and unable to function properly.

Vitamin B12 is unique among vitamins because it is not produced by plants or animals but by certain bacteria and archaea. Animals obtain B12 by consuming foods contaminated with these microorganisms or, in the case of ruminants like cows, through bacterial production in their digestive systems. Humans must obtain B12 through dietary sources or supplements, as our bodies cannot synthesise it. While bacteria in the human colon do produce B12, this occurs too far along the digestive tract for absorption.

The absorption of vitamin B12 is a complex process requiring intrinsic factor, a protein produced by gastric parietal cells in the stomach. This protein binds to B12 and allows it to be absorbed in the terminal ileum of the small intestine. Conditions affecting the stomach or small intestine, including pernicious anaemia (where antibodies attack intrinsic factor or parietal cells), can therefore impair B12 absorption, even when dietary intake is adequate. The liver can store several years' worth of B12, which means deficiency typically develops slowly over time.

Animal-Based Foods High in Vitamin B12

Animal products are the richest natural sources of vitamin B12, as the vitamin accumulates in animal tissues, particularly in the liver and muscles. Understanding which foods contain the highest amounts can help ensure adequate intake through diet.

Meat and Offal

Beef liver is one of the most concentrated sources of vitamin B12, with a single 100g serving providing approximately 60–65 micrograms—far exceeding daily requirements. Lamb liver and chicken liver are similarly rich sources. Regular cuts of beef, lamb, and pork also contain substantial amounts of B12, typically providing 1–3 micrograms per 100g serving. Offal, whilst not commonly consumed in modern UK diets, represents an exceptionally nutrient-dense option.

Fish and Seafood

Fish and shellfish are excellent sources of vitamin B12. Mackerel, salmon, tuna, and sardines all provide significant amounts, with mackerel offering approximately 8–12 micrograms per 100g. Shellfish are particularly rich: clams can contain over 80 micrograms per 100g, whilst mussels, oysters, and crab also provide substantial quantities. These foods offer the additional benefit of omega-3 fatty acids and other essential nutrients.

Dairy Products and Eggs

Dairy products provide moderate amounts of vitamin B12 in a highly bioavailable form. Milk, cheese, and yoghurt all contribute to B12 intake, with a 200ml glass of milk providing approximately 1 microgram. Mature cheeses like cheddar tend to contain higher concentrations than some softer varieties, though levels vary between products. Eggs contain approximately 0.5–1.0 microgram of B12 per large egg, primarily in the yolk. Whilst these foods contain less B12 than meat or fish, they are consumed more regularly by many people and therefore represent important dietary sources, particularly for vegetarians who consume dairy and eggs.

Plant-Based and Fortified Sources of B12

Naturally occurring vitamin B12 is virtually absent from plant foods, presenting a significant challenge for those following vegan or strict vegetarian diets. However, fortified foods and certain specialised products can help bridge this nutritional gap.

Fortified Foods

Many plant-based products available in UK supermarkets are now fortified with vitamin B12. Fortified breakfast cereals are among the most reliable sources, with some brands providing 25–100% of the Reference Nutrient Intake (RNI) of 1.5 micrograms per serving—always check the nutrition label as fortification levels vary considerably between products. Plant-based milk alternatives, including soya, almond, oat, and coconut milk, are frequently fortified with B12, typically providing 0.38–0.5 microgram per 100ml. Nutritional yeast, popular in vegan cooking, is often fortified and can provide 2–8 micrograms per tablespoon, though unfortified varieties contain negligible amounts.

Some meat alternatives, such as veggie burgers, sausages, and other processed plant-based products, are fortified with B12 and other nutrients to more closely match the nutritional profile of meat. Certain brands of spreads, including yeast extracts like Marmite, contain added B12.

Limitations and Considerations

It is important to note that some foods claimed to contain B12, such as spirulina, seaweed, and unwashed organic vegetables, contain B12 analogues—compounds structurally similar to B12 but not reliably bioactive in humans. These sources cannot be depended upon to meet B12 requirements. The NHS and British Dietetic Association advise that individuals following plant-based diets should consume fortified foods regularly or take B12 supplements. Those following vegan diets should discuss supplementation with their GP or a registered dietitian to ensure adequate intake.

How Much B12 Do You Need Daily?

The recommended daily intake of vitamin B12 varies according to age, physiological status, and individual circumstances. Understanding these requirements helps ensure adequate intake whilst avoiding unnecessary supplementation.

Standard Recommendations

According to UK dietary reference values, adults aged 19 and over require approximately 1.5 micrograms of vitamin B12 daily (Reference Nutrient Intake or RNI). This recommendation is based on the amount needed to maintain normal blood levels and prevent deficiency. Infants and children have age-specific requirements: 0.3 micrograms (0-6 months), 0.4 micrograms (7-12 months), 0.5 micrograms (1-3 years), 0.8 micrograms (4-6 years), 1.0 microgram (7-10 years), and 1.2 micrograms (11-14 years). Adolescents aged 15-18 require 1.5 micrograms. These amounts are generally easily met through a varied diet containing animal products.

Increased Requirements

Certain groups require higher intakes or have increased risk of deficiency. Pregnant women should aim for 1.5 micrograms daily, whilst breastfeeding women require 2 micrograms to ensure adequate transfer to the infant through breast milk. Older adults do not have higher RNI values, but they may experience reduced absorption efficiency due to decreased stomach acid production or atrophic gastritis, making fortified foods or supplements advisable.

Individuals taking certain medications may need additional B12. Metformin, commonly prescribed for type 2 diabetes, can reduce B12 absorption over time. The MHRA Drug Safety Update (June 2022) advises that patients on long-term metformin therapy should have their B12 levels monitored periodically. Proton pump inhibitors (PPIs) and H2-receptor antagonists, used for acid reflux and peptic ulcers, reduce stomach acid production and may impair B12 absorption with long-term use.

Absorption Considerations

It is worth noting that the body can only absorb approximately 1.5–2 micrograms of B12 per meal through the intrinsic factor mechanism, with passive absorption accounting for roughly 1% of higher doses. This means that consuming very large amounts in a single meal offers limited additional benefit, and regular intake throughout the day or week is more effective than occasional large doses from food sources.

Signs You May Not Be Getting Enough B12

Vitamin B12 deficiency develops gradually, as the liver stores substantial reserves that can last several years. Recognising the signs of deficiency is important for early intervention and preventing potentially irreversible neurological damage.

Haematological Symptoms

The most common manifestation of B12 deficiency is megaloblastic anaemia, characterised by the production of abnormally large, immature red blood cells. This leads to symptoms including persistent tiredness and fatigue, weakness, breathlessness (particularly on exertion), and pale skin. Some individuals experience heart palpitations or become dizzy. These symptoms develop because the blood cannot carry oxygen efficiently around the body. However, these signs are non-specific and can occur in many other conditions, so medical assessment is essential.

Neurological and Cognitive Symptoms

Vitamin B12 is crucial for maintaining the myelin sheath that protects nerve fibres. Deficiency can cause peripheral neuropathy, presenting as pins and needles (paraesthesia), numbness, or altered sensation, typically beginning in the hands and feet. Some people experience problems with balance and coordination, muscle weakness, or difficulty walking. Cognitive symptoms may include memory problems, confusion, difficulty concentrating, or mood changes including depression and irritability. Importantly, neurological symptoms can occur even without anaemia, and in severe, prolonged deficiency, irreversible neurological damage can occur, emphasising the importance of early detection.

Other Manifestations

Some individuals develop a sore, red tongue (glossitis) or mouth ulcers. Visual disturbances can occur if the optic nerve is affected, though this is rare. Unexplained weight loss or loss of appetite may also occur.

When to Seek Medical Advice

If you experience persistent tiredness, neurological symptoms such as pins and needles, or any combination of the above symptoms, contact your GP. This is particularly important if you follow a vegan or vegetarian diet, are over 60, have a digestive condition affecting absorption (such as Crohn's disease, coeliac disease, or have had gastric surgery), or take medications that may affect B12 absorption. Severe or progressive neurological symptoms, visual disturbances, or significant difficulty walking warrant urgent medical assessment.

Your GP can arrange blood tests to check B12 levels, along with a full blood count and folate levels. Additional tests may include checking for antibodies associated with pernicious anaemia. If deficiency is confirmed, treatment depends on the underlying cause and may include dietary modification, oral supplements, or intramuscular B12 injections. It's important not to take high-dose folic acid supplements alone if B12 deficiency is suspected, as this may mask the blood changes while allowing neurological damage to progress.

If you suspect a medication may be affecting your B12 levels, discuss this with your healthcare provider and consider reporting suspected side effects through the MHRA Yellow Card Scheme.

Frequently Asked Questions