Adults need a small amount of vitamin B12 every day: about 1.5 micrograms in UK guidance and 2.4 micrograms in the US. It comes naturally from animal foods such as meat, fish, eggs and dairy. Vegans, older adults, people with pernicious anaemia and those taking certain medicines are most at risk of running low.
Key takeaways
- The NHS says adults aged 19 to 64 need about 1.5 micrograms of B12 a day; the US RDA is 2.4 micrograms.
- Meat, fish, eggs and dairy supply B12 naturally; fruit, vegetables and grains do not.
- Vegans need fortified foods or a supplement, because reliable plant sources are limited.
- Low B12 is more common with age, pernicious anaemia and some medicines such as PPIs.
- Tiredness, pins and needles or a sore red tongue are reasons to see a doctor, not to self-diagnose.
What does vitamin B12 do?
Vitamin B12 (cobalamin) is a water-soluble vitamin that your body needs to make healthy red blood cells, keep the nervous system working and release energy from food. You only need a tiny amount, measured in micrograms (µg, millionths of a gram), but going short for a long time can cause real problems.
When B12 runs low, the body makes fewer, abnormally large red blood cells that cannot carry oxygen well. This is a type of anaemia. Low B12 can also affect the nerves, sometimes before anaemia shows up in a blood test. The good news is that deficiency is usually easy to prevent with the right foods, and it can be treated once found.
How much vitamin B12 do you need a day?
Recommendations differ a little between countries because they are set using slightly different methods:
| Guideline | Adults |
|---|---|
| NHS (UK), adults 19–64 | About 1.5 µg a day |
| US recommended dietary allowance (RDA) | 2.4 µg a day |
The NHS notes that most people can get enough B12 from a varied diet that includes animal foods. Because the body stores B12 in the liver, a shortfall usually builds up slowly, over months or years, rather than overnight.
Which foods contain vitamin B12?
B12 is made by bacteria, not by plants or animals themselves. Animals absorb it and store it in their tissues, which is why meat, fish, eggs, milk and cheese are the natural sources. Fruit, vegetables and grains do not naturally contain it. Some foods have B12 added: certain breakfast cereals, unsweetened soya drinks and yeast extract or nutritional yeast flakes.
Research on B12 content (Watanabe and colleagues, 2014) gives a sense of the amounts in some everyday foods:
| Food | B12 content | Notes |
|---|---|---|
| Cow's milk | About 0.3–0.4 µg per 100 g | A 250 ml glass gives roughly 0.8–1 µg |
| Cheese | Keeps about 20–60% of the milk's B12 | Depends on the type of cheese |
| Whole eggs | About 0.9–1.4 µg per 100 g | Mostly in the yolk; only about 4–9% is absorbed from cooked eggs |
| Meat and fish | Reliable natural sources | Part of a normal mixed diet |
| Fortified cereals, soya drinks, yeast extract | Varies by product | Check the label; important for vegans |
The egg figure is worth noticing: eggs contain B12, but the body absorbs relatively little of it, so they should not be your only source. Read more in our guide to eggs and their nutrition facts.
In practical terms, a mixed diet covers B12 easily. A breakfast of eggs and cheese, a glass of milk or a pot of yogurt during the day and a fish or meat dinner, such as grilled salmon (about 460 kcal and 40 g protein per serving in Sporty's per-serving estimates; real values depend on recipe and portion), all add to the total.
If you rely on fortified products, make checking the label a habit. Two soya drinks or two breakfast cereals on the same shelf can differ: one may have added B12 and the other none, so look at the ingredients list and nutrition panel rather than assuming. The amount is usually shown in micrograms per serving or as a percentage of the reference intake.
Who is most at risk of low vitamin B12?
- Vegans. Without animal foods, the only reliable sources are fortified foods and supplements. The NHS says sources for vegans are limited and a supplement may be needed.
- Vegetarians who eat little dairy or eggs. Intake can be low if these foods are eaten only occasionally.
- Older adults. According to the NHS, B12 deficiency affects about 1 in 10 people aged 75 or over and 1 in 20 people aged 65 to 74.
- People with pernicious anaemia. In this autoimmune condition the immune system attacks cells in the stomach, so B12 cannot be absorbed from food. It is the most common cause of B12 deficiency in the UK.
- People taking certain medicines. The NHS lists some anticonvulsants and proton pump inhibitors (PPIs, used for acid reflux) as medicines that can reduce absorption.
- People on very restrictive diets or with a poor diet over a long period.
Pregnant and breastfeeding women who follow a vegan diet should talk to their doctor or midwife about B12, since the baby depends on the mother's supply.
Are there good plant sources of vitamin B12?
This is where a lot of myths circulate. The same 2014 review looked at plant foods often promoted as B12 sources:
- Nori (dried seaweed): contained about 77.6 µg per 100 g dry weight in the authors' analyses, but the evidence that it improves B12 status in people is limited.
- Tempeh: 0.7–8.0 µg per 100 g, probably from bacteria during fermentation. Too variable to rely on.
- Dried shiitake mushrooms: 1.3–12.7 µg per 100 g dry weight, and you would need about 50 g of dried mushrooms a day to meet the RDA.
- Spirulina and similar algae supplements: often contain pseudovitamin B12, a form that is inactive in humans. The authors concluded they are not suitable B12 sources.
The bottom line for vegans is simple: use fortified foods and/or a B12 supplement, and do not count on seaweed, mushrooms or algae. Our article on plant protein covers the protein side of a meat-free diet.
What are the signs of vitamin B12 deficiency?
The NHS lists symptoms including:
- extreme tiredness and a lack of energy
- pins and needles, muscle weakness or problems with vision
- a sore, red tongue and mouth ulcers
- low mood, problems with memory, understanding or judgement
Some of these can appear without anaemia. They also overlap with many other conditions, including iron deficiency (see iron-rich foods), so the right step is a blood test through your doctor, not guessing. Deficiency caused by poor absorption, such as pernicious anaemia, is usually treated with injections, and diet alone will not fix it.
Does a calorie deficit put you at risk?
Eating less overall means less room for nutrients, and some diets cut out whole food groups. If you are losing weight on a plan that drops meat, fish, eggs or dairy, make sure fortified foods or a supplement fill the gap. A lower-calorie diet can still include B12-rich foods: a çılbır breakfast (about 380 kcal) or a bowl of yogurt with fruit (about 230 kcal) in Sporty's per-serving estimates. For the wider picture, see vitamins and minerals in a calorie deficit. Sporty tracks calories and macros rather than vitamins, so use the food list above as your checklist.
Can you take too much vitamin B12?
The NHS says there is not enough evidence to show what the effects of taking high doses of B12 supplements every day might be, and that taking too much of any supplement could be harmful. Most people who eat animal foods do not need a supplement at all. If you think you might, especially if you are older, vegan, pregnant or take long-term medication, ask a doctor or pharmacist which dose suits you.
Frequently asked questions
How much vitamin B12 do adults need per day?
The NHS says adults aged 19 to 64 need about 1.5 micrograms a day. The US recommended dietary allowance is 2.4 micrograms a day.
What foods are highest in vitamin B12?
Animal foods such as meat, fish, eggs, milk and cheese are the natural sources. Fortified breakfast cereals, fortified soya drinks and fortified yeast extract or nutritional yeast also provide it.
Do vegans need a B12 supplement?
Usually yes, or they need to eat B12-fortified foods regularly. Plant foods such as seaweed, mushrooms and spirulina are not reliable sources.
Who is at risk of B12 deficiency?
Vegans, older adults, people with pernicious anaemia, people taking some medicines such as PPIs or anticonvulsants, and people on very restrictive diets. A doctor can check levels with a blood test.
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This article is general information, not medical advice. If you have a health condition, are pregnant or under 18, talk to a doctor or registered dietitian before changing your diet.