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 happens if vitamin B12 is low?
Your body needs B12 to make healthy red blood cells and to keep your nervous system working. When levels run low, two things can happen: you can develop anaemia, and your nerves and brain can be affected. Problems usually build slowly, because the NHS says the body’s B12 stores can last around 2 to 5 years.
- Anaemia: feeling weak or tired, shortness of breath, headaches and palpitations.
- Mouth: a sore or red tongue, sometimes with mouth ulcers.
- Nerves: pins and needles, numbness, muscle weakness, problems with balance and coordination, and problems with your vision.
- Mood and memory: problems with memory, understanding and judgement, and changes that can range from mild depression or anxiety to confusion.
You don’t have to be anaemic to be low. NICE tells doctors not to rule out B12 deficiency just because a blood count looks normal, and it notes that symptoms vary from person to person and often overlap with other conditions.
What happens if it isn’t treated?
Most people respond well to treatment. Left untreated, though, the NHS says nerve problems can sometimes be irreversible, and the longer it goes on, the higher the chance of permanent damage. Severe anaemia of any kind can also strain the heart.
See a GP if you have any of these symptoms, especially numbness, tingling, balance problems or changes in your vision. Tell them about any B12 or multivitamin you already take, as it can affect the blood test.
What causes low B12 and who is at risk?
| Cause | Who it affects |
|---|---|
| Pernicious anaemia | The most common cause in the UK: the immune system stops the stomach absorbing B12. NICE now calls it autoimmune gastritis. The NHS says it’s more common in women around 60, people with a family history and people with another autoimmune condition |
| Vegan or very restricted diet | B12 isn’t found naturally in plant foods, so vegans need fortified foods or a supplement |
| Medicines | Metformin for diabetes, proton pump inhibitors (PPIs) such as omeprazole, and H2 blockers. NICE also lists colchicine, pregabalin, topiramate and some epilepsy medicines. Don’t stop a prescribed medicine: ask your GP whether your B12 should be checked |
| Gut conditions and surgery | Such as Crohn’s disease, coeliac disease, stomach surgery or some weight loss operations |
| Older adults | Absorption falls with age. A 2004 review found low B12 in more than 1 in 5 older people, most often because the stomach releases less B12 from food |
| Nitrous oxide | Recreational use of nitrous oxide (“laughing gas”) is a NICE risk factor |
| Heavy drinking | Can affect absorption and diet |
For how B12 works alongside folate, B6 and the other B vitamins, and the best foods for each, see our guide to B vitamins.
Diagnosis and treatment
See your GP if you think you might be low. A blood test can usually confirm it.
How the B12 test works (NICE NG239)
- Who gets tested: NICE says to offer a test to people with at least one common symptom and at least one common risk factor, such as a vegan diet, metformin or PPIs, or autoimmune gastritis.
- The test: either total B12 or active B12, taken before any B12 treatment starts.
- The results: a total B12 under 180 nanograms per litre confirms deficiency, 180 to 350 is a grey area that may need a further test, and over 350 makes deficiency unlikely. Local labs may use their own cut-offs.
- What can skew it: shop B12 supplements can raise the result without fully treating a deficiency, and the combined contraceptive pill can lower total B12 without causing a deficiency.
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.
Related guides
- Signs of low vitamin D and how it is tested.
- Which deficiencies are linked to dark circles.
- For how B12 compares with B6, see vitamin B6 vs B12 in our B6 guide.
- Vitamins for women over 40.
- Eating a vegan diet? Omega 3 is another nutrient to plan for: see omega 3 for vegans.
- Men on metformin or over 65: see vitamins for men over 50 for where B12 fits.
- Not sure whether tingling is down to B12? Our guide to pins and needles covers the other common causes and when to see a GP.
- If you keep getting ulcers, see our guide to mouth ulcers: causes and when to see a GP.
- Multivitamins for vegans and older adults.
- Who needs one, which form and how much to take: see our guide to vitamin B12 supplements.
- If you’re vegan, don’t rely on algae for B12. See why spirulina’s B12 is mostly inactive.
- Pins and needles only in the thumb and first fingers, worse at night? It may be carpal tunnel rather than low B12.
- B12 deficiency and premature grey hair.
Evopure doesn’t make a B12 supplement, and none of our products treats B12 deficiency: if you think you’re low, see your GP for a blood test. Magnesium contributes to a reduction of tiredness and fatigue. Our reishi hot chocolate contains a little natural caffeine from the cacao.
The FSA’s 10mg a day figure for CBD is precautionary advice rather than a legal limit, set while longer-term safety research continues. At Evopure we think it is a very cautious figure, and many adults use more. If you go above it, increase slowly, and check with your GP or pharmacist first if you take any medication.
Our products are for adults (18+). We don’t recommend our products during pregnancy or breastfeeding. If you take any medication, check with your GP or pharmacist first.
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.
What happens if vitamin B12 is low?
Your body can’t make enough healthy red blood cells, and your nerves can be affected. The NHS lists tiredness, pins and needles, a sore red tongue, mouth ulcers, memory and mood changes and vision problems. Left untreated, some nerve damage can be permanent, so see a GP.
Can you have low B12 without anaemia?
Yes. The NHS says some symptoms can appear before anaemia develops, and NICE tells doctors not to rule out B12 deficiency just because a blood count is normal.
Should I take B12 before my blood test?
Talk to your GP first. NICE says blood for B12 tests should be taken before treatment starts, because supplements can raise the result without fully treating a deficiency. If you already take B12 or a multivitamin, tell your GP.
Can metformin or omeprazole cause low B12?
They can. The NHS lists metformin and proton pump inhibitors (PPIs) such as omeprazole among the medicines that can lower B12. Don’t stop a prescribed medicine on your own: ask your GP whether your B12 should be checked.
Sources
- NHS. Vitamin B12 or folate deficiency anaemia, and its symptoms, causes and complications pages.
- NICE. Vitamin B12 deficiency in over 16s: diagnosis and management (NG239), 2024.
- Andrès E et al. Vitamin B12 (cobalamin) deficiency in elderly patients. CMAJ, 2004. PMID 15289425.
- NHS. B vitamins and folic acid.
- NHS. Tiredness and fatigue.
This guide is general information, not medical advice.
