Vitamin B12 is a water-soluble vitamin that’s essential for your health. It plays a really important role in red blood cell production and helps your nervous system to function properly. If you're deficient in vitamin B12 it can cause a wide range of symptoms — like tiredness, pins and needles, and memory problems. You can check to see if you're getting enough vitamin B12 with a blood test.

What is vitamin B12?

Vitamin B12, also called cobalamin, is a type of B vitamin. It's a water-soluble vitamin which means it can dissolve in water. Your body can store vitamin B12 for years in your liver.

What does vitamin B12 do?

Vitamin B12 is essential for:

  • red blood cell production
  • DNA synthesis
  • a healthy nervous system

Vitamin B12 is also important for a healthy heart and is critical during pregnancy for a baby’s developing brain and nervous system.

Vitamin B12 deficiency

If you’re deficient in vitamin B12, it can cause a wide range of problems.


A lack of vitamin B12 means your body can’t make enough red blood cells or each blood cell doesn’t have enough haemoglobin — this is called anaemia. This means you can’t transport enough oxygen around your body.

Nerve damage

Long-term vitamin B12 deficiency can cause nerve damage. This is because vitamin B12 is needed to make myelin — a protective sheet that covers your nerves. If this isn’t caught early enough it can cause irreversible nerve damage. It’s rare, but sometimes your optic nerve might become damaged and cause blurred vision.

Balance issues

Long-term vitamin B12 deficiency can also cause problems with your balance.

Psychological issues

Vitamin B12 deficiency might cause you to feel confused or depressed. It’s also linked to poor memory and dementia.

Symptoms of vitamin B12 deficiency

The signs and symptoms of vitamin B12 deficiency include:

  • extreme tiredness
  • weakness
  • pins and needles (especially in your hands and feet)
  • mouth ulcers
  • a swollen and sore tongue (glossitis)
  • blurred vision
  • poor memory
  • depression

In rare cases, it can cause heart and fertility problems.

If you have any of these symptoms it’s really important to check your vitamin B12 levels. Some of these symptoms, like nerve damage, can be irreversible.

Causes of vitamin B12 deficiency

A number of things can cause vitamin B12 deficiency, these include:

  • pernicious anaemia — your immune system mistakenly attacks cells in your stomach that produce intrinsic factor (which you need to absorb vitamin B12)
  • diet — plant-based diets, such as vegan, vegetarian, and dairy-free diets are sometimes lacking in vitamin B12
  • medication — some medications, like proton pump inhibitors (PPIs), can inhibit absorption of vitamin B12

You’re also more at risk of vitamin B12 deficiency if you:

  • are pregnant or breastfeeding
  • are over 50 years — because you might stop producing enough hydrochloric acid in your stomach which is needed for absorption of vitamin B12
  • suffer from a gastrointestinal disorder — like coeliac disease or Crohn’s disease

You should also keep in mind that folic acid supplements can mask vitamin B12 deficiency. This is because it can improve your symptoms so much that they’re not noticeable.

How to test your vitamin B12 levels

You can check your vitamin B12 levels with a simple finger-prick blood test. An active vitamin B12 test is the best way to measure your levels — this is the amount of vitamin B12 your body can actually use.

Thriva home finger-prick blood test vitamin B12

How to treat vitamin B12 deficiency

There are lots of things you can do to increase your vitamin B12 levels.


Foods rich in vitamin B12 include:

  • organ meats — like liver and kidney are the richest sources of vitamin B12
  • beef
  • fish — like clams, sardines, salmon, and tuna
  • milk and dairy products
  • eggs

Vitamin B12 is only naturally available in meat, fish or dairy. But there are fortified plant-based sources of vitamin B12 like:

  • fortified milk alternatives
  • fortified cereals
  • fortified nutritional yeast


You can also take a vitamin B12 supplement. It’s usually available as cyanocobalamin — a form which your body can easily convert and use. It's also possible to get a vitamin B12 injection — this is especially useful if your deficiency is caused by absorption issues in your stomach. The form hydroxocobalamin can be given every three months.


National Institue of Health (2018). Office of dietary supplements. Vitamin B12: Fact sheet for health professionals. Retrieved 28 September 2018 from

Reynolds, E. (2006). Vitamin B12, folic acid, and the nervous system. The Lancet Neurology, 5(11), 949-960.

Stabler, S. P. (2013). Vitamin B12 deficiency. New England Journal of Medicine, 368(2), 149-160.

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Aisling Moran BSc (Hons)

Written by Aisling Moran BSc (Hons)

11th Aug 2021 • 4 min read