What does vitamin B12 do and how can you get enough?
Vitamin B12 benefits are often talked about in relation to energy, but this vitamin does far more than that. It helps with red blood cell production, supports the nervous system, and plays an important role in DNA synthesis, so low levels can affect how you feel in several different ways.
Vitamin B12 deficiency can develop for different reasons, including not getting enough B12 from food, poor absorption, stomach or bowel conditions, or the use of certain medications longer term. In the UK, the most common cause is pernicious anaemia, an autoimmune condition that stops the body absorbing vitamin B12 properly.
What is vitamin B12?
Vitamin B12, also called cobalamin, is a water-soluble vitamin your body needs to make red blood cells, support the nervous system, and help with DNA synthesis. It is obtained mainly from foods of animal origin, including dairy products.
Our body cannot make vitamin B12 on its own, so you need to get it from your diet or, in some cases, from supplements or prescribed treatment. Diets including meat, fish, and dairy products usually provide enough vitamin B12.
Vitamin B12 is also different from some other nutrients because low intake is not the only issue. Some people eat foods that contain enough B12 but still become deficient because their body cannot absorb it properly.
What does vitamin B12 do in our body?
Vitamin B12 helps several important systems in the body work properly. It supports:
- red blood cell production
- nervous system health
- DNA synthesis
When your red blood cells are not being produced properly, you may feel tired, weak, or short of breath. When the nervous system is affected, symptoms can include pins and needles, poor concentration, memory changes, and low mood. Vitamin B12 deficiency can be easy to miss, especially in the early stages. Symptoms can come on gradually and may overlap with everyday issues such as stress, poor sleep, a busy routine, or other health concerns.
Signs of low vitamin B12
Symptoms linked to low vitamin B12 may include:
- tiredness or low energy
- feeling weak
- headaches
- poor concentration or brain fog
- pins and needles
- memory changes
- low mood, irritability, or emotional ups and downs
Vitamin B12 deficiency does not always look the same from person to person. Some people have clear symptoms, while others may have only mild or very subtle signs at first. Blood results do not always fully reflect how someone feels, which is why testing can be a useful starting point. Results still need to be looked at alongside symptoms and medical history to understand what may be causing the deficiency and what the most appropriate next step may be.
Why vitamin B12 levels can drop
The common causes include:
1. Not getting enough from your diet
Some people develop a vitamin B12 deficiency because they do not get enough from food. This risk is higher in people who do not regularly eat meat, fish, dairy, or other vitamin B12 sources, and in people following a vegan diet who do not take supplements or eat fortified foods.
2. Poor absorption
Absorption problems are a major reason why B12 can be low even when food intake seems reasonable. Pernicious anaemia is the most common cause of vitamin B12 deficiency in the UK. It is an autoimmune condition that affects the stomach and stops the body absorbing vitamin B12 properly
3. Stomach or bowel conditions
Stomach and bowel issues can reduce the absorption of B12 causing levels to drop. Stomach conditions such as gastritis (chronic inflammation of your stomach) or a history of previous stomach surgery including a gastric bypass can cause B12 levels to be low. Some bowel problems such as Coeliac or Crohn’s disease can also reduce absorption in the bowel which can cause people to become deficient .
4. Some medications
Some medicines can affect vitamin B12 levels. These include proton pump inhibitors such as omeprazole, lansoprazole, and pantoprazole, as well as metformin and nitrous oxide (“laughing gas”). If you have been using any of these over the long term and are concerned about symptoms of vitamin B12 deficiency, it is worth having your levels checked.
5. Long-term changes that build slowly
Stores of vitamin B12 in the body can last around 2 to 5 years without being replenished. A deficiency may take time to show up after a dietary change, which is one reason people can feel unwell before they realise it may be due to their B12 levels.
Foods high in vitamin B12
Foods high in vitamin B12 are a good place to start for those wanting to improve or maintain healthy levels. Vitamin B12 is naturally present in foods of animal origin, including fish, meat, poultry, eggs, and dairy products. Examples include:
- fish
- meat
- poultry
- eggs
- milk, yoghurt, and cheese
- yeast extracts
- fortified breakfast cereals
If you have cut back on animal products, changed your diet recently, or tend to eat a narrow range of foods, it is worth taking a closer look at where your vitamin B12 is coming from.
Top 5 ways to get enough vitamin B12
1. Eat regular foods high in vitamin B12
For many people, the most straightforward step is to regularly include B12-rich foods in meals across the week. Meat, fish, eggs, milk, yoghurt, cheese, and fortified cereals can all help.
2. Check fortified foods if you eat little or no animal produce
If you eat little or no meat, fish, eggs, or dairy, fortified foods can help you maintain your vitamin B12 intake. People on a vegan diet who do not take B12 supplements or eat foods fortified with vitamin B12 are at risk of deficiency.
3. Do not ignore ongoing symptoms
It is easy to brush off symptoms such as tiredness, poor concentration, or feeling unlike yourself, especially when life is busy. But if tiredness lasts for weeks, or you notice symptoms such as pins and needles or ongoing brain fog, it is worth looking into possible nutritional or medical causes.
4. Review medicines and health conditions that may affect absorption
If you take medicines such as metformin or a proton pump inhibitor, or if you have a stomach or bowel condition, it is sensible to keep vitamin B12 on your radar.
5. Consider testing if you are at risk or want a clearer picture
Testing can be a practical next step when diet, symptoms, or risk factors suggest vitamin B12 may need checking.
The role of at-home testing
At-home testing can be useful when you want an indication as to whether you have low vitamin B12 levels. Boots Vitamin B12 Blood Test uses a finger-prick blood sample to check your vitamin B12 levels. Results are ready usually within 48-72 hours of your sample arriving at the laboratory.
An at-home test can help you decide on next steps, however should not replace a medical assessment with a healthcare professional where symptoms are significant, persistent, or getting worse. A result may help guide a conversation with your GP, especially if you have symptoms, follow a restrictive diet, take medicines linked to lower B12, or have a condition that may affect absorption.
When to speak to a GP
It is worth speaking to a GP if your symptoms are persistent or are starting to affect your daily life. The same applies if you have known risk factors for low vitamin B12, such as following a vegan diet, taking medicines such as metformin or proton pump inhibitors, or having stomach or bowel problems that may affect absorption.
If your test result is low, or you still have persistent symptoms despite making changes to your diet, it is worth speaking with a medical professional who can carry out a more detailed review. This is especially important because low vitamin B12 can sometimes be linked to poor absorption rather than low intake alone.
Frequently asked questions
1. What does vitamin B12 do for your body?
Vitamin B12 helps with red blood cell production, supports neurologic function, and plays a role in DNA synthesis.
2. What foods are high in vitamin B12?
Common sources include fish, meat, poultry, eggs, milk, yoghurt, cheese, yeast extracts, and fortified breakfast cereals.
3. What are the signs of low vitamin B12?
Possible signs include tiredness, weakness, poor concentration, headaches, pins and needles, memory changes, irritability, and low mood. Symptoms can vary from person to person.
4. Can you have low vitamin B12 even if you eat well?
Yes. Some people have low vitamin B12 because their body cannot absorb it properly. Pernicious anaemia, stomach conditions, bowel conditions, and some medications can all play a part.
5. Is an at-home vitamin B12 test worth doing?
It can be a useful way to check your vitamin B12 level if you have symptoms or risk factors and want more clarity. It should be used sensibly, and persistent or concerning symptoms should be discussed with a GP.
In summary
Vitamin B12 benefits go well beyond energy. This vitamin supports red blood cell production, nervous system health, and DNA synthesis, and low levels may affect both physical and emotional wellbeing. You can help support healthy levels by eating foods high in vitamin B12, paying attention to symptoms and risk factors, and using testing appropriately when you want a clearer picture. If you want a more detailed assessment, a Boots Vitamin B12 Blood Test or Boots Tired All The Time Energy Blood Test can help you understand your level, but ongoing or concerning symptoms should always be followed up with a healthcare professional.
References
1. National Institute for Health and Care Excellence. Vitamin B12 deficiency in over 16s: diagnosis and management. NICE guideline NG239. London: NICE; 2024. https://www.nice.org.uk/guidance/ng239
2. GPnotebook. Assessment, investigation and diagnosis of B12 deficiency. 2025.https://gpnotebook.com/en-GB/pages/haematology/vitamin-b12-deficiency/assessment-investigation-and-diagnosis-of-b12-deficiency
3. NHS. Vitamin B12 or folate deficiency anaemia. 2026. https://www.nhs.uk/conditions/vitamin-b12-or-folate-deficiency-anaemia/
4. Lacombe V, Vinatier E, Roquin G, Salhi A, Remen T, Deshayes C, et al. Oral vitamin B12 supplementation in pernicious anemia. Am J Clin Nutr. 2024. https://ajcn.nutrition.org/article/S0002-9165(24)00484-2/fulltext
5. Ankar A, Kumar A. Vitamin B12 deficiency. In: StatPearls. Treasure Island (FL): StatPearls Publishing; 2024. https://www.ncbi.nlm.nih.gov/books/NBK441923/