Vitamin B12 Deficiency: Signs, Causes and Who Is at Risk
Vitamin B12 deficiency can cause extreme tiredness, pins and needles, a sore red tongue, mouth ulcers and problems with memory or mood. These signs overlap with many other conditions, so the only way to know is a blood test arranged by a doctor.
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Key takeaways
- Common signs include extreme tiredness, lack of energy, pins and needles, a sore red tongue and mouth ulcers.
- In the UK, the most common cause is pernicious anaemia, an autoimmune condition that stops B12 being absorbed — not diet.
- Vegans, older adults and people taking certain medicines (such as some anticonvulsants and PPIs) are more likely to be affected.
- Diagnosis needs a blood test. Treatment is usually tablets or injections and works well when started early.
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What vitamin B12 does
Vitamin B12 helps your body make healthy red blood cells and keeps your nervous system working properly. When you don't have enough, your body can produce abnormally large red blood cells that can't carry oxygen well. This is a type of anaemia. B12 deficiency can also affect the nerves even before anaemia develops.
Common signs of vitamin B12 deficiency
According to the NHS, a lack of vitamin B12 (or folate) can cause a wide range of problems, including:
- extreme tiredness and a lack of energy
- pins and needles
- a sore and red tongue
- mouth ulcers
- muscle weakness
- problems with your vision
- psychological problems, from mild depression or anxiety to confusion
- problems with memory, understanding and judgement
Many of these signs are non-specific: tiredness, low mood and tingling have lots of possible causes. That is why symptoms are a reason to get checked, not a diagnosis.
Why early diagnosis matters
Many symptoms improve with treatment, but the NHS notes that some problems caused by the deficiency can be irreversible if it is left untreated for a long time. If you recognise several of the signs above, don't wait for them to get worse.
What causes it
| Cause | What happens |
|---|---|
| Pernicious anaemia | The immune system attacks cells in the stomach, so B12 from food can't be absorbed. It is the most common cause in the UK. |
| Diet low in B12 | Uncommon, but possible with a vegan diet without fortified foods or supplements, a very restrictive diet, or a poor diet over a long time. |
| Medicines | Some medicines, including certain anticonvulsants and proton pump inhibitors (PPIs, used for acid reflux), can reduce absorption. |
Who is more at risk
- Older adults. The NHS reports that B12 or folate deficiency affects around 1 in 10 people aged 75 or over, and 1 in 20 people aged 65 to 74.
- People following a vegan diet without B12-fortified foods or supplements, because B12 comes naturally from animal foods.
- People taking medicines that affect absorption, especially long term.
- People with conditions affecting the stomach or gut that interfere with absorption.
How it is diagnosed and treated
A doctor can usually confirm a deficiency with your symptoms and a blood test. Treatment depends on the cause:
- Injections are usually used first to restore B12 levels.
- Then, if the cause is diet-related, tablets may be enough; if the body can't absorb B12 from food, regular injections may be needed long term.
- Improving your diet can help prevent a diet-related deficiency coming back.
Don't start, stop or change treatment without speaking to your doctor.
Food sources of vitamin B12
Vitamin B12 is found in meat, fish, eggs and dairy products, and in specially fortified foods. If you eat few or no animal products, check labels for fortified foods and ask a pharmacist or doctor whether a supplement is right for you.
When to see a doctor
See a doctor if you have symptoms of vitamin B12 deficiency, particularly if you are older, follow a vegan diet, or take medicines that can affect absorption. Ask whether a blood test is appropriate.
Watch: the short version
VitaminsShort
3 Signs of Vitamin B12 Deficiency You Shouldn’t Ignore
Watch on YouTube (opens in a new tab)Common questions
Can I just take a B12 supplement instead of getting tested?
It is better to see a doctor first, because the cause matters. For example, if your body can't absorb B12 from food, as in pernicious anaemia, the NHS explains that regular injections rather than diet-related tablets may be needed.
Which foods contain vitamin B12?
Vitamin B12 is found naturally in meat, fish, eggs and dairy products, and is added to some fortified foods such as certain breakfast cereals and plant-based drinks.