Is a vitamin B12 deficiency affecting your health?

With an estimated 6 million people in the UK experiencing a vitamin B12 deficiency, it’s surprising how few people are aware of its health impacts.

A vitamin B12 deficiency may not sound like much, but this important nutrient is a vital part of many processes in the body. If deficient, you can experience several unwanted symptoms – from fatigue to muscle weakness. 

Ensuring you have sufficient amounts of B12 in your diet may make all the difference in preventing conditions such as dementia and anaemia. 

A vitamin B12 deficiency is easily detected through a blood test, and in most cases, can be easily reversed. 

In this blog, we discuss: 

What is vitamin B12?

Vitamin B12 (also known as cobalamin) is a water-soluble nutrient that is used in many of the body's processes. 

B12 helps your body with: 

  • DNA production 
  • The normal functioning of the nervous system 
  • Cell repair 
  • Metabolism of fats and proteins  

Vitamin B12 comes almost entirely from animal products.  

Sources of B12 include: 

  • Meat  
  • Fish  
  • Milk 
  • Eggs 

However, there are natural plant sources of B12, such as: 

  • Yeast extract (found in marmite and nutritional yeast) 
  • Unsweetened fortified plant milk  
  • Fortified breakfast cereals 

If you are following a vegan or plant-based diet, you can read more about achieving a balanced diet in our plant-based diets and nutrition blog. 

What’s the difference between total B12 and active B12? 

Once in the body, vitamin B12 is bound to proteins called transcobalamin; 70% is transported by transcobalamin I (TCI or haptocorrin) and cannot be used by the majority of the body’s cells — this is known as inactive B12. The other 30% of vitamin B12 is transported on the active protein transcobalamin II (TCII or holo-transcobalamin) and can be used in cells [1]. 

Total B12 is a measure of both inactive and active forms of B12. It’s the levels of active B12 which are most important if you’re worried you may be deficient or have symptoms.  

You can read more about the difference between total B12 and active B12 in our blog.   

The human body stores several years' worth of vitamin B12 in the liver, so it can often manage these reserves if it is not provided with B12 from an external source. However, eventually, these reserves will run out too and can lead to a deficiency.  

What is vitamin B12 deficiency? 

A lack of or deficiency of Vitamin B12 occurs when the body isn’t getting the required daily intake.  

This could be due to a mixture of things, including: 

  • Lack of vitamin B12 in the diet  
  • Problems absorbing the vitamin from the gut  
  • Increased use of vitamin B12 in the body 

The recommended daily amount of vitamin B12 varies depending on your age.  

The daily RDI for vitamin B12 micrograms (mcg) [2]: 

Age Recommended amount (mcg)
1 year 0.5
2-3 years 0.5
4-6 years 0.8
7-10 years 1.0
11-14 years 1.2
15-18 years 1.5
19+ years 1.5


What are the symptoms of B12 deficiency?

As vitamin B12 is necessary for so many functions in the body, the symptoms of a deficiency are wide-ranging. 

 Symptoms of a B12 deficiency typically include: 

  • Fatigue 
  • Breathlessness 
  • Loss of appetite 
  • Stomach issues 
  • Weight loss 
  • Mouth and tongue ulcers 
  • Nerve damage 
  • Pins and needles or loss of sensation in fingers and toes 
  • Muscle weakness 
  • Sight and memory problems 
  • Mood changes and depression 
  • Palpitations 

You should speak to a medical professional, or test yourself for a deficiency if you are experiencing any of these symptoms, as a long-term deficiency of B12 can be detrimental to your health.  


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What causes vitamin B12 deficiency, and who is at risk?

The most common cause of vitamin B12 deficiency is an autoimmune disease called pernicious anaemia. This condition causes the body to produce an antibody that attacks the protein responsible for extracting vitamin B12 from food.  

Other people at higher risk of a vitamin B12 deficiency include people: 

  • With a gut autoimmune disease – such as Crohn’s disease or coeliac. This is because the body attacks the gut and can affect the gut lining, meaning that B12 is not absorbed properly.
  • On metformin – people who are on metformin are at greater risk of developing a vitamin B12 deficiency. The government have recently announced new advice that recommends you are screened for a vitamin B12 deficiency if you are on long-term metformin [3].  
  • Over the age of 60 – it is thought that up to one in five people over the age of 60 may be affected by a B12 deficiency due to the decline in absorption rates as you get older [4].  

How is vitamin B12 deficiency diagnosed?

A vitamin B12 deficiency is diagnosed through a simple blood test, and to help you get the answers you need, Medichecks has a range of tests for B12 and pernicious anaemia

It is important to note that only active vitamin B12 can be used in the body, so measuring the total level of B12 could give misleading results and fail to diagnose a deficiency. 

For example, even if the results showed a normal range of vitamin B12 in the blood, the levels of useful active B12 could still be low. This is why Medichecks measures active B12 so that you can get clear, accurate and useful results. 

How is a vitamin B12 deficiency treated?

A vitamin B12 deficiency or pernicious anaemia should be diagnosed and treated promptly — some problems caused by the condition can be irreversible, though complications are rare [5].  

Potential complications caused by prolonged vitamin B12, or folate deficiency include: 

  • Damaged nervous system 
  • Temporary infertility 
  • Heart conditions or heart failure 
  • Pregnancy complications and congenital disabilities 
  • Anaemia 
  • Chronic tiredness and low energy levels 
  • Low mood 
  • Increased risk of dementia 
  • Increased risk of developing stomach cancer if you have pernicious anaemia 

Once a blood test has diagnosed a vitamin B12 deficiency, depending on the cause, your doctor will prescribe treatment of either daily supplements, tablets, or injections. 

In some cases, including more vitamin B12 in your diet can treat the deficiency and prevent its return. However, if your intake still isn’t high enough, you may need to take daily tablets in between meals or have regular injections which may need to be continued for the rest of your life. 

What can I do now? 

If you are concerned about having a B12 deficiency or fall into any of the high-risk categories, Medichecks’ simple Vitamin B12 (Active) Blood Test can help you get the answers you need. Your results are complete with qualified doctors’ advice which you can then take to your GP to discuss which treatment is most suited to you. 


  1. O’Leary, F. and Samman, S., 2010. Vitamin B12 in Health and Disease. Nutrients, 2(3), pp.299-316. 
  2. 2022. [online] Available at: <> [Accessed 7 July 2022]. 
  3. GOV.UK. 2022. Metformin and reduced vitamin B12 levels: new advice for monitoring patients at risk. [online] Available at: <> [Accessed 7 July 2022]. 
  4. 2022. Prevalence | Background information | Anaemia - B12 and folate deficiency | CKS | NICE. [online] Available at: <,are%20deficient%20in%20vitamin%20B12.> [Accessed 7 July 2022]. 
  5. Jatoi, S., Hafeez, D., Riaz, S., Ali, A., Ghauri, M. and Zehra, M., 2020. Low Vitamin B12 Levels: An Underestimated Cause Of Minimal Cognitive Impairment And Dementia. Cureus,. 


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