Last updated: October 2026
The NHS lists extreme tiredness, a lack of energy, pins and needles, a sore red tongue, mouth ulcers, muscle weakness, vision problems, low mood and memory problems as symptoms of vitamin B12 deficiency. The most common cause in the UK is pernicious anaemia. A GP blood test confirms it, and early treatment matters.
Below: the symptoms, who’s at risk, how it’s diagnosed and treated, the best food sources, and how much B12 you need.
Vitamin B12 deficiency symptoms
According to the NHS, a lack of vitamin B12 (or folate) can cause:
| Area | Symptoms |
|---|---|
| Energy | Extreme tiredness, a lack of energy, muscle weakness |
| Nerves | Pins and needles, problems with your vision |
| Mouth | A sore and red tongue, mouth ulcers |
| Mind | Low mood or anxiety, confusion, problems with memory, understanding and judgement |
Some of these can happen even before anaemia develops. The NHS stresses diagnosing and treating it early, because some nerve problems can become permanent. See brain fog and why am I always tired?
What causes low B12?
| Cause | Who it affects |
|---|---|
| Pernicious anaemia | The most common cause in the UK: the immune system stops the stomach absorbing B12 |
| Vegan or very restricted diet | B12 isn’t found naturally in plant foods, so vegans need fortified foods or a supplement |
| Medicines | Including some anticonvulsants, long-term acid-reducing medicines and metformin for diabetes |
| Gut conditions and surgery | Such as Crohn’s disease or stomach surgery |
| Older age | Absorption falls with age |
| Heavy drinking | Can affect absorption and diet |
Diagnosis and treatment
See your GP if you think you might be low. A blood test can usually confirm it. Treatment depends on the cause:
- If it’s your diet: B12 tablets, plus more B12-rich or fortified foods.
- If you can’t absorb B12 (such as pernicious anaemia): injections, often for life.
Don’t self-treat for long without a diagnosis, as supplements can mask the problem and delay finding the cause.
Foods high in vitamin B12
The NHS lists meat, fish, milk, cheese, eggs and some fortified breakfast cereals as good sources. For vegans, fortified plant milks, yeast extract, fortified cereals and a supplement are the reliable options. Vitamin B12 contributes to the reduction of tiredness and fatigue and to normal energy-yielding metabolism.
For other nutrients linked to energy, see best supplements for energy, iron deficiency symptoms and foods high in magnesium.
How much B12 do you need?
- Adults aged 19 to 64 need about 1.5 micrograms a day, according to the NHS.
- If you eat meat, fish or dairy, you should get enough from your diet.
- The NHS says taking 2mg or less a day of B12 in supplements is unlikely to cause harm.
FAQs
What are the first signs of B12 deficiency?
Extreme tiredness and a lack of energy are often first, along with pins and needles, a sore red tongue or mouth ulcers.
What is the most common cause of B12 deficiency in the UK?
Pernicious anaemia, where the immune system stops the stomach absorbing vitamin B12.
Can low B12 cause anxiety or brain fog?
Yes. The NHS lists psychological problems, from low mood or anxiety to confusion and memory problems, as possible symptoms.
Do vegans need a B12 supplement?
Usually, yes. B12 isn’t found naturally in plant foods, so vegans need fortified foods or a supplement.
How is B12 deficiency treated?
With tablets if it’s due to diet, or injections if you can’t absorb B12, such as with pernicious anaemia.
Sources
- NHS. Vitamin B12 or folate deficiency anaemia.
- NHS. B vitamins and folic acid.
- NHS. Tiredness and fatigue.
This guide is general information, not medical advice.
