What is a vitamin B12 deficiency: symptoms, causes & prevention

Vitamin B12 is essential for keeping your nervous system working properly and keeping the blood healthy so it can oxygenate your cells. It’s a crucial vitamin for a healthy body and good mental wellbeing, but it’s not something we can make ourselves. Vitamin B12 needs to be eaten as part of a balanced diet, but some of us simply aren’t getting enough. A vitamin B12 deficiency can pass undetected for years and could affect your neurological, and mental health, as well as your ability to remain well. This guide will help you identify the varied symptoms of a B12 deficiency and give details on the causes and treatment.

What is a vitamin B12 deficiency?

Vitamin B12 (also called ‘cobalamin’) helps the body make red blood cells and DNA. It also plays a vital role in the regulation of your nervous system. Your body doesn’t produce B12, so the only way to get it is to make sure you have plenty of B12-rich foods in your diet.

A vitamin B12 deficiency can cause your body to make abnormally large red blood cells that do not function correctly. Your red blood cells are responsible for transporting oxygen from your lungs to your cells via a protein called haemoglobin.

Adults need about 1.5 micrograms of vitamin B12 per day. B12 occurs naturally in foods from animals, like fish, poultry, meat, dairy, and eggs. If you eat a variety of these foods you are likely to get enough vitamin B12. However, fruit and vegetables do not contain vitamin B12 so vegans and vegetarians need to get their B12 from supplements or from eating foods which have been fortified with vitamin B12 such as cereals, plant-based milk and marmite.

What are the symptoms of a vitamin B12 deficiency?

Vitamin B12 deficiency symptoms develop gradually and are very varied. Because of the insidious nature of vitamin B12 deficiency it can be years before you realise you’re deficient and diagnosed with it. The symptoms and signs of vitamin B12 deficiency relate to the anaemia and neurological problems it causes. These signs and symptoms include:

  • Headaches
  • Pale skin
  • Heart palpitations
  • fatigue
  • Loss of appetite
  • Shortness of breath
  • Low energy levels
  • Depression
  • Mouth ulcers
  • Memory loss
  • Impaired vision
  • Pins and needles

What are the causes of a vitamin B12 deficiency?

Most of the causes for low vitamin B12 are related to medical issues, medicines or factors that aren’t preventable.

Pernicious anaemia

Pernicious anaemia is the most common cause of vitamin B12 deficiency in the UK. This is where your immune system attacks healthy cells in your stomach, which stops you from properly absorbing the B12 you eat.

Medical conditions

Some digestive medical conditions can affect how much B12 your body absorbs. These include people with:

  • Atrophic gastritis (chronic inflammation of your stomach lining)
  • Crohn’s disease
  • Coeliac disease
  • Part or whole of their stomach removed

Vegan or vegetarian diet

You may be at risk of low vitamin B12 if you’re a vegetarian or vegan. This can be prevented by adding foods that have been fortified with vitamin B12 such as some breakfast cereals, plant-based milks and marmite.


Certain medications also prevent your body from absorbing enough B12. This includes heartburn medications and diabetes medications.

How to prevent and treat vitamin B12 deficiency

You can prevent a dietary vitamin B12 deficiency by eating more foods that contain vitamin B12 such as:

  • Seafood and fish
  • Meat
  • Poultry
  • Dairy
  • Eggs

Take a multivitamin

People who struggle to get enough B12 from their food may like to try a multivitamin instead. You should consult with your doctor about which supplement is right for your needs.

Stop smoking

Some studies have found smoking can increase your chances of vitamin deficiency. Smoking is the leading cause of preventable death in the UK and contributes to lung cancer and coronary heart disease. If you are a smoker and want to quit the habit, you can find practical tips and advice here.


Vitamin B12 deficiency treatment varies depending on the cause of the deficiency. Treatment needs to be directed by your GP or, if you have damage to your nerves, a Haematologist. If your deficiency is caused by diet, the treatment may be relatively straightforward.

Vitamin injections

If you’re diagnosed with vitamin B12 deficiency, the initial treatment will be to give you B12 injections.  Further management will depend on the cause of the deficiency. If the deficiency is caused by a lack of vitamin B12 in your diet you will be advised by your doctor to take hydroxycobalamin tablets and given advice on how to increase your intake of vitamin B12.

How can I raise my B12 levels fast?

People with B12 deficiency need to have injections from their GP or a specialist in order to quickly raise their B12 levels.

Is vitamin B12 deficiency serious?

Vitamin B12 deficiency can cause severe complications. It can result in anaemia, nerve damage and psychiatric problems.

What is considered low vitamin B12?

The ‘normal’ range of serum B12 varies between laboratories. However, as a guide, a typical NHS laboratory has a ‘normal’ range between 180 to 700 ng/L. What is a clinically normal level is not clear but it is thought that a level below 200 ng/L identifies 97% of people with B12 deficiency.

How long does it take to recover from a vitamin B deficiency?

Once treatment begins, vitamin B12 deficiency symptoms normally improve within days or a few weeks.

Vitamin B12 deficiency can cause permanent nerve damage, neurological issues, and debilitating tiredness. A Bluecrest active vitamin B12 home test kit can measure your levels quickly and easily. It’s a simple finger prick test that takes minutes to do and you’ll get results in as little as 8 days, allowing for faster treatment. For more information on diet and nutrition, you can visit the Bluecrest blog.