Vitamin B12 – what it is and what to eat

Vitamin B12 is essential for many of the body’s processes. In this article we tell you what it is, why it’s important and how not to become deficient.

Approx read time: 5 mins
Vitamin B12


I cannot stress enough how important it is to have adequate intake and stores of Vitamin B12. This vitamin is involved in so many of the body’s processes, including:

  • red blood cell formation
  • manufacture of DNA (pretty fundamental!)
  • nervous system* and immune function
  • control of an amino acid called homocysteine, high levels of which are a precursor to heart disease.

*In relation to nerves B12 helps form the essential coating which helps them to pass signals.

Where does B12 come from?

B12 is non-existent in plant foods unless they are fortified. We get it from animal foods – meat, fish, poultry, and dairy and eggs to a lesser degree. Although some breakfast cereals are also fortified with it, which is why we put cereals such as Sultana Bran and Weetabix on the Nutrition for Everyone plan – and plenty of mushrooms on the veggie versions.

How does it work?

When you eat foods that contain B12 your stomach acid detaches the B12 from the food to free it up; it then moves down the tubes where it couples up with a special protein called Intrinsic Factor (IF). It needs IF to carry it through into your bloodstream because it can’t get through on its own.

Think of them in an embrace, going up to an opening in your intestinal wall and jumping through into your bloodstream, B12 can’t do it on its own. IF is produced by cells in your stomach lining, by the way

How much do you need?

The amount you need varies by sex and age but in the UK for adults aged 19-64 it’s:

  • 1.1mg a day for women
  • 1.3mg a day for men

Good sources

Per 100g of each food, here’s the amount of B12:

  • Crab 11.5 – yes ELEVEN POINT FIVE!
  • Salmon 3.2 
  • Mozzarella 2.3
  • Tuna 2.2
  • Steak 2.2
  • Weetabix 2.1 (2 Weetabix would be about 1 microgram, so ⅔ of your daily requirement – now you know why I invented Nuushabix….)
  • Prawns 1.7
  • Eggs 1.1 (this would be 2 large eggs)
  • Cod 0.9
  • Greek yog 0.8 
  • Milk 0.5 (a glass of milk would be four times this amount, so it would give you 2 micrograms.
  • Chicken 0.3

People with an increased risk of deficiency

  1. Those who take acid-controlling meds such as Omeprazole (which it seems is a large proportion of the population). You see, if you are suppressing stomach acid it can’t then detach B12 from food. Arrgghh.
  2. Those who have pernicious anaemia which is where your stomach cells don’t produce any Intrinsic Factor because they may have been killed off by antibodies. So the B12 doesn’t have its pal to jump through the intestine with so it’s just left waiting around, crying, and then just swooshes down through your gut and out of your bum 🙂
  3. Those who restrict animal foods in their diet and don’t supplement or consume fortified foods, particularly vegans. Vegetarians who eat eggs and dairy are generally good for B12. Or it can just be people who eat a poor quality diet without very many B12 foods.
  4. Older people – that’s because as we age we can start to produce fewer digestive enzymes such as Intrinsic Factor and may have less acidic stomach juices. In people under 60 the prevalence of deficiency is about 6%, in those older than 60 it rises to 20%.
  5. Those who don’t eat much fibre. That’s because your gut bacteria need fibre to thrve and they actually produce B12. Clever little critters.
  6. Anyone who has undergone intestinal surgery such as gastric by-pass.
  7. People with gastrointestinal conditions such as colitis, that can affect nutrient absorption.

Vitamin B12 deficiency can have these symptoms

  • fatigue and tiredness
  • heavy limbs
  • pale skin
  • breathlessness
  • anxiety, irritability and depression
  • tinnitus
  • mouth ulcers
  • pale and sore tongue
  • tingling hands or feet

Vitamin B12 and anaemia

In order to make red blood cells to carry oxygen around your body you need good levels of B12, as well as folate and iron. Healthy red blood cells are circular with a dip in the middle, sort of like a round Werther’s Original. They take haemoglobin on board, which carries that life-giving substance, oxygen.

Without enough B12 your red blood cells become an odd shape, and often larger. This weird shape makes them unable to carry haemoglobin. Therefore no oxygen will jump on board either because its mate haemoglobin isn’t there. Pretty serious!

High B12?

If you’ve had a blood test and have high B12 it may be because you are taking high dose supplements. As B12 is water soluble most excess should be excreted but in cases of very high supplementation side effects can occur such as spots and acne, headaches, diarrhoea and bloating

Should you supplement?

If you have symptoms, some of which can crossover with other conditions, then you can ask your GP for a test. The problem is some tests will only look for total B12 and not whether it’s active or not. You could use a service such Medichecks to check the amount of active B12 and you can take that to your GP and ask about courses of action.

If you are deficient you can try addressing it with diet first and get re-tested after a few months; if it has made little difference then consider a supplement. If you are vegan or you restrict the animal foods in your diet or if you fit any of the potential deficiency criteria above then a supplement is sensible.

Your liver stores enough B12 for 3-5 years of average daily requirement, so deficiencies can take that amount of time to show up. Don’t forget there are fortified foods such as some breakfast cereals, nutritional yeast and plant milks that can be useful additions to your diet.

Suggested recipes for vitamin B12 boost

Do you want better health?

The Nutrition for Everyone plan will help you maximise the essential nutrients your body needs for robust health.

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Thank you for reading this article. Please note that while we share a lot of awesome information and research you should be aware our articles are strictly for informational purposes and do not constitute medical advice intended to diagnose, cure, treat or prevent any disease.