Vitamin B12, or cobalamin, is an essential nutrient that your body cannot produce, making dietary intake vital for health. This water-soluble vitamin supports red blood cell formation, nervous system function, and DNA synthesis. Good sources of B12 are predominantly animal-based foods such as meat, fish, dairy, and eggs, whilst those following plant-based diets must rely on fortified foods or supplements. Understanding where to obtain adequate B12 is crucial, as deficiency can lead to anaemia and potentially irreversible neurological damage. This guide explores the best dietary sources, signs of deficiency, and when supplementation may be necessary.

What Is Vitamin B12 and Why Do You Need It?

Vitamin B12, also known as cobalamin, is an essential water-soluble vitamin that plays a crucial role in numerous bodily functions. Unlike some vitamins that the body can produce, B12 must be obtained entirely through diet or supplementation, making awareness of good dietary sources particularly important for maintaining optimal health.

This vitamin is fundamental to the production of red blood cells, which carry oxygen throughout your body. Without adequate B12, red blood cells cannot develop properly, leading to a condition called megaloblastic anaemia where cells become abnormally large and ineffective. Additionally, B12 is vital for maintaining the health of your nervous system, as it contributes to the formation and maintenance of the protective myelin sheath that surrounds nerve fibres.

Key functions of vitamin B12 include:

• DNA synthesis and cell division

• Neurological function and nerve cell maintenance

• Red blood cell formation

• Metabolism of fatty acids and amino acids

• Energy production at the cellular level

The body stores vitamin B12 primarily in the liver, with reserves typically lasting several years. However, this storage capacity means that deficiency can develop slowly and insidiously, often going unnoticed until symptoms become pronounced. The recommended daily intake (RNI) for adults in the UK is 1.5 micrograms, according to NHS guidance. This requirement remains unchanged during pregnancy but increases slightly to around 2 micrograms during breastfeeding.

It's important to note that vitamin B12 interacts with folate metabolism. Treating someone with folic acid alone when they have an undiagnosed B12 deficiency can improve anaemia symptoms while allowing potentially irreversible neurological damage to progress. Understanding where to obtain this essential nutrient is the first step in preventing deficiency and maintaining long-term health.

Best Dietary Sources of Vitamin B12

Vitamin B12 is naturally found almost exclusively in animal-derived foods, which presents particular challenges for those following plant-based diets. Understanding the richest sources can help you ensure adequate intake through dietary choices.

Animal-based sources (naturally rich in B12):

Meat and poultry provide B12, though content varies significantly. Beef liver is one of the most concentrated sources available—a single 75g serving can provide well over 1,000% of the daily requirement. Red meats like beef and lamb are excellent sources, typically providing 1–2 micrograms per standard portion. Poultry such as chicken and turkey contain lower amounts, generally less than 0.5 micrograms per portion.

Fish and seafood are particularly valuable sources. Salmon, trout, tuna, and sardines all contain high levels of B12, with some varieties of shellfish—especially clams, mussels, and crab—providing exceptional amounts. A 75g portion of cooked salmon typically delivers approximately 2.5 micrograms.

Dairy products including milk, cheese, and yoghurt contribute meaningful amounts of B12 to the diet. A 200ml glass of semi-skimmed milk provides roughly 1 microgram, whilst hard cheeses and yoghurt offer similar benefits. These sources are particularly important for vegetarians who exclude meat and fish.

Eggs contain B12 primarily in the yolk, with two large eggs providing approximately 1.5 micrograms.

Fortified foods for plant-based diets:

For vegans and those avoiding animal products, fortified foods become essential. Many breakfast cereals, plant-based milk alternatives (soya, almond, oat), nutritional yeast, and meat substitutes are now fortified with B12. However, it's important to check labels carefully, as fortification levels vary considerably between brands and products. In the UK, fortified foods are regulated under food law by the Department of Health and Social Care (DHSC) and the Food Standards Agency (FSA).

It's worth noting that some non-fortified plant foods (such as seaweed, spirulina, and tempeh) are sometimes claimed to contain B12, but they typically contain inactive B12 analogues that the human body cannot utilise effectively. These should not be relied upon as primary sources of vitamin B12.

Signs You May Need More Vitamin B12

Vitamin B12 deficiency can develop gradually, and early symptoms are often subtle and non-specific, making recognition challenging. Understanding the warning signs is crucial for timely intervention and prevention of potentially irreversible neurological damage.

Common early symptoms include:

• Persistent tiredness and weakness that doesn't improve with rest

• Pale or slightly yellow-tinged skin (due to anaemia)

• Breathlessness and dizziness, particularly on exertion

• Mouth ulcers or a sore, red tongue (glossitis)

• Pins and needles sensations (paraesthesia) in hands or feet

• Disturbed vision or changes in visual perception

• Mood changes, including depression or irritability

• Problems with memory, concentration, or cognitive function

These neurological symptoms occur because B12 deficiency affects the myelin sheath protecting nerve fibres. If left untreated, some neurological effects may become permanent, which is why early detection is particularly important.

Seek urgent medical attention if you experience progressive neurological symptoms, significant visual changes, difficulty walking, or if symptoms develop during pregnancy.

Groups at higher risk of deficiency:

Certain populations face elevated risk and should be particularly vigilant. Vegans and strict vegetarians who consume no animal products require fortified foods or supplements. Older adults (over 50) may develop reduced stomach acid production, impairing B12 absorption. People with pernicious anaemia—an autoimmune condition affecting intrinsic factor production—cannot absorb B12 effectively from food. Those with gastrointestinal conditions such as Crohn's disease, coeliac disease, or who have undergone gastric surgery may have impaired absorption.

When to contact your GP:

If you experience persistent fatigue, neurological symptoms like numbness or memory problems, or belong to a high-risk group, arrange a consultation with your GP. Initial investigations typically include a full blood count, serum B12 and folate levels. According to NICE Clinical Knowledge Summaries, further testing may include intrinsic factor antibodies if pernicious anaemia is suspected, and occasionally more specialised tests such as methylmalonic acid (MMA) or holotranscobalamin when the diagnosis remains uncertain.

When to Consider B12 Supplements

Whilst obtaining vitamin B12 through dietary sources is ideal, supplementation becomes necessary or advisable in specific circumstances. Understanding when supplements are appropriate, and which forms are most effective, helps ensure optimal B12 status.

Situations requiring supplementation:

Diagnosed deficiency confirmed by blood tests requires treatment, typically with high-dose supplements or injections depending on severity and underlying cause. For pernicious anaemia or malabsorption conditions, intramuscular injections (hydroxocobalamin) are standard treatment in the UK, usually administered initially as six injections over two weeks, then maintenance injections every two to three months for life. For neurological involvement, more intensive treatment may be required.

Vegan and vegetarian diets necessitate either consistent consumption of fortified foods or daily oral supplementation. The Vegan Society recommends either eating fortified foods two to three times daily to obtain at least 3 micrograms, or taking a daily supplement providing at least 10 micrograms, or a weekly supplement of 2,000 micrograms.

Older adults should be assessed if they show symptoms of deficiency, as absorption naturally decreases with age. Those taking certain medications, particularly metformin (for diabetes) or proton pump inhibitors (for acid reflux), should be monitored for B12 deficiency symptoms and tested if they develop, as these drugs can interfere with B12 absorption, according to MHRA guidance.

Types of supplements available:

Oral supplements come in various forms including cyanocobalamin (the most common and stable form) and methylcobalamin (a naturally occurring form). Both are effective for most people. For dietary deficiency, oral cyanocobalamin at doses of 50–150 micrograms daily between meals is typically recommended. Sublingual tablets, which dissolve under the tongue, are popular though there is no official evidence confirming superior absorption compared to swallowed tablets in people with normal digestive function.

Safety considerations:

Vitamin B12 supplements are generally very safe, as excess amounts are excreted in urine. However, always inform your GP about supplements you're taking, particularly if you have kidney problems or are undergoing medical investigations, as unexpectedly high B12 levels can sometimes be a marker of other underlying conditions. The NHS advises that taking 2 mg or less of B12 supplements daily is unlikely to cause harm. Never self-diagnose deficiency—always seek proper medical assessment and blood testing before starting high-dose supplementation.

If you experience any suspected side effects from B12 medicines or supplements, you can report them via the MHRA Yellow Card Scheme.

Frequently Asked Questions