Tiredness is not always a sleep problem, and tingling feet are not always about circulation. Vitamin B12 deficiency tends to arrive quietly, with changes that are easy to put down to stress, a busy year or getting older. Some people develop nerve symptoms before anything shows up on a routine blood count, and by the time the problem is recognised, a few of those symptoms can be slow to recover.
The good news is that B12 deficiency is common, testable and very treatable once it is found. This guide explains what B12 does, the signs that deserve attention, who is most likely to run low, how clinicians test for it and why the cause of the deficiency shapes the treatment.
- What vitamin B12 does
- Why absorption is the weak point
- Vitamin B12 deficiency: the quiet signs people explain away
- Who is most likely to have low B12
- Medicines linked with low B12
- Where B12 comes from in food
- How testing works
- How vitamin B12 deficiency treatment depends on the cause
- When to seek help, and how quickly
- What to bring to the appointment
- Questions people ask
- Sources
What vitamin B12 does
Vitamin B12, also called cobalamin, is needed to make DNA and healthy red blood cells and to keep the protective coating around nerves in good order. The NIH Office of Dietary Supplements notes that it works closely with folate, and a shortage of either can cause a type of anaemia in which red blood cells are too large and too few.
The liver stores several years’ worth of B12. That is why B12 deficiency usually develops slowly, often long after a change in diet, the start of a new medicine or the onset of a stomach problem. It also explains why people rarely connect their symptoms to the cause.
Adults need very little of it: the US recommended amount is 2.4 micrograms a day, rising to 2.6 micrograms in pregnancy and 2.8 micrograms while breastfeeding. For most people with low B12, the difficulty is not eating too little but absorbing too little.
Why absorption is the weak point
Getting B12 from food into the blood takes several steps, and each is a place where things can go wrong:
- Stomach acid releases B12 from the protein in food.
- Cells in the stomach lining make a protein called intrinsic factor, which binds the B12.
- The combined B12 and intrinsic factor are absorbed at the far end of the small intestine, the terminal ileum.
Low stomach acid disrupts step one. Autoimmune gastritis, the cause of pernicious anaemia, destroys the cells that make intrinsic factor and blocks step two. Crohn’s disease or surgery affecting the ileum interferes with step three. The B12 in fortified foods and supplements is not bound to protein, so it skips step one, which is why older adults and people on acid-reducing medicines are often advised to rely on those sources.
Vitamin B12 deficiency: the quiet signs people explain away
The NHS lists a wide range of possible symptoms. They fall into three broad groups, and people may have signs from one, two or all three.
| Group | What it can feel like | How it often gets explained away |
|---|---|---|
| Blood (anaemia) | Tiredness, lack of energy, breathlessness on exertion, pale or slightly yellow skin, palpitations, headaches | “Just a busy spell” or “out of shape” |
| Nerves | Pins and needles or numbness in the feet or hands, a feeling of walking on cotton wool, unsteadiness, especially in the dark, muscle weakness | “Poor circulation”, “getting older”, “bad shoes” |
| Brain and mood | Forgetfulness, slower thinking, trouble concentrating, irritability, low mood | Stress, menopause, poor sleep |
| Mouth and gut | A sore, smooth, red tongue, mouth ulcers, reduced appetite, weight loss | A minor mouth problem |
Unsteadiness deserves special mention. B12 deficiency can damage the nerve pathways that tell your brain where your feet are without you looking at them. People notice it on stairs, on uneven ground or when the lights go off, and it can raise the risk of falls. Our guide to fall prevention covers other reasons balance changes with age, but new unsteadiness should always be checked rather than accepted.
Every symptom in the table has other possible causes, from thyroid disease and iron deficiency to diabetes and depression. A cluster of them, particularly with one of the risk factors below, is a good reason to ask about testing.
Who is most likely to have low B12
- People with autoimmune gastritis (pernicious anaemia). One of the most common causes in the UK and other high-income countries. It is more likely in people with other autoimmune conditions such as thyroid disease or type 1 diabetes.
- Older adults. The ODS notes that a significant minority of older adults have atrophic gastritis, which reduces stomach acid and the release of B12 from food.
- Vegans, and vegetarians who eat few eggs or dairy foods. B12 occurs naturally only in animal foods, so unfortified plant diets do not provide it.
- People who have had stomach or bowel surgery, including many types of weight-loss surgery and operations that remove the ileum.
- People with Crohn’s disease, coeliac disease or other conditions that affect the small intestine.
- Long-term users of certain medicines, described below.
- Heavy drinkers, through poor diet and effects on absorption.
- Babies of mothers with low B12, especially if exclusively breastfed. Pregnant and breastfeeding vegans should discuss B12 with their midwife or doctor.
Medicines linked with low B12
Metformin, the most widely used medicine for type 2 diabetes, is associated with lower B12 levels over time. Diabetes guidelines recommend periodic B12 checks for people on long-term metformin, particularly if they develop anaemia or nerve symptoms. This matters because diabetic nerve damage and B12 nerve damage can look alike, and one can be mistaken for the other. Our article on preventing prediabetes covers the everyday side of blood sugar control.
Proton pump inhibitors such as omeprazole, and H2 blockers such as famotidine, reduce stomach acid. Used for two years or more, they have been associated with lower B12, according to the ODS. By contrast, nitrous oxide, whether from repeated anaesthesia or recreational use, inactivates B12 and can cause severe nerve damage quickly, even in people whose levels were previously normal.
None of these is a reason to stop a prescribed medicine. They are reasons to ask your prescriber whether checking your B12 would be sensible.
Where B12 comes from in food
These approximate amounts come from the ODS consumer fact sheet. Fortified products vary by brand, so check labels.
| Food | Serving | Approximate B12 | Compared with 2.4 mcg daily need |
|---|---|---|---|
| Beef liver, cooked | 85 g (3 oz) | About 70 mcg | Many times over |
| Clams, cooked | 85 g (3 oz) | About 17 mcg | Several times over |
| Fortified nutritional yeast | Quarter of a cup | Varies widely; can exceed the daily need | Check the label |
| Salmon, cooked | 85 g (3 oz) | About 2.6 mcg | All of it |
| Tuna, canned | 85 g (3 oz) | About 2.5 mcg | All of it |
| Beef mince, cooked | 85 g (3 oz) | About 2.4 mcg | All of it |
| Milk | 1 cup | About 1.3 mcg | Around half |
| Plain yoghurt | 1 small pot | About 1 mcg | Around 40 per cent |
| Fortified breakfast cereal | 1 serving | Often about 0.6 mcg | About a quarter |
| Egg | 1 large | About 0.5 mcg | About a fifth |
Plant foods such as seaweed, mushrooms and tempeh are sometimes promoted as B12 sources, but the amounts are small and unreliable, and some contain inactive forms. For vegans, fortified foods eaten more than once a day or a regular supplement are the dependable options. Building meals with enough protein also helps, and our guide to protein after 50 offers ideas.
How testing works
A clinician will start with your symptoms, diet, medicines and medical history. In the UK, the NICE guideline on vitamin B12 deficiency in over 16s, published in 2024, sets out how testing should be interpreted. In outline:
- First test: either total B12 or active B12 (holotranscobalamin). Active B12 is preferred in pregnancy, when total B12 naturally falls.
- Reading total B12: NICE treats a level below 180 ng/L as indicating deficiency, 180 to 350 ng/L as indeterminate and above 350 ng/L as making deficiency unlikely.
- Indeterminate results: a further test such as methylmalonic acid (MMA) can help. MMA rises when B12 is low but can also rise with kidney problems, so it is interpreted with kidney function in mind.
- Full blood count: useful for spotting anaemia and enlarged red cells, but a normal count does not rule out B12 deficiency, especially when nerve symptoms come first.
- Looking for the cause: if pernicious anaemia is suspected, antibodies to intrinsic factor may be checked. A negative result does not fully exclude it.
If you can, discuss testing before starting a B12 supplement, because supplements can raise blood levels and make the picture harder to read. Do not delay urgent care for rapidly worsening symptoms to arrange a test first.
How vitamin B12 deficiency treatment depends on the cause
The NHS treatment guidance reflects a simple principle: if the gut cannot absorb B12, it needs to bypass the gut.
| Cause | Typical approach |
|---|---|
| Low intake from diet | B12 tablets, together with dietary changes or fortified foods; usually short term unless the diet stays low in B12 |
| Pernicious anaemia or other absorption problems | Injections, often a loading course followed by maintenance injections, usually for life |
| Nerve or neurological symptoms | Prompt treatment with injections, with specialist advice; nerve symptoms can take months to improve and may not fully resolve if treatment is delayed |
| Medicine-related | Depends on the medicine and the level; tablets or injections, with ongoing monitoring |
High-dose oral B12 can work even in some absorption problems, because a small fraction is absorbed without intrinsic factor, and some clinicians use it. The choice depends on the cause, how severe the deficiency is and the person’s preference, and it should be made with a clinician.
One caution matters a great deal. High doses of folic acid can correct the anaemia caused by B12 deficiency while the nerve damage carries on. Always tell your clinician about every supplement you take, and do not treat suspected B12 deficiency with folic acid alone. Folic acid advice for pregnancy is separate and remains important; discuss it with your maternity team.
B12 from food and supplements has not been shown to cause harm at high intakes in healthy people, which is why no upper limit has been set. That does not mean extra B12 improves energy or memory in people who are not deficient; trials have not shown that it does.
When to seek help, and how quickly
Book a routine appointment if tiredness, tingling, mouth changes or low mood persist for more than a few weeks, especially if you have a risk factor. Seek urgent care for new difficulty walking, rapidly spreading numbness or weakness, confusion, severe breathlessness, chest pain, fainting or sudden changes in vision. These symptoms can have urgent causes that have nothing to do with vitamins.
What to bring to the appointment
- When symptoms started and whether they are getting worse
- Any changes in balance, sensation, memory or mood
- Your usual diet, including whether you avoid meat, fish, eggs or dairy
- Past stomach or bowel surgery and any digestive conditions
- The names and doses of all medicines and supplements, including how long you have taken metformin or acid-reducing medicines
- Any family history of pernicious anaemia or autoimmune conditions
If forgetfulness is part of the picture, our guide to brain health covers the wider set of factors that affect memory and thinking.
Questions people ask
Can you have B12 deficiency without anaemia?
Yes. Nerve and mental symptoms can appear before the blood count changes, which is why a normal full blood count does not rule out low B12.
Can a vegan diet provide enough B12?
Not without fortified foods or a supplement. With either of those used consistently, vegans can maintain healthy levels.
How long does it take to feel better after treatment?
Energy often improves within days to weeks once treatment starts. Blood counts recover over several weeks. Nerve symptoms are slower and can take months; some may not fully resolve if they were present for a long time before treatment.
Is tingling always a sign of low B12?
No. Diabetes, nerve compression, alcohol, thyroid disease, some medicines and anxiety can all cause tingling. A clinical assessment helps tell them apart.
Are B12 injections better than tablets?
It depends on the cause. Injections are standard when absorption is the problem or nerves are affected. Tablets are often enough when the cause is diet.
Should I take B12 for energy if my levels are normal?
There is no good evidence that extra B12 boosts energy in people who are not deficient. If you are tired all the time, the cause is worth finding.
Sources
- NIH Office of Dietary Supplements: Vitamin B12 fact sheet for health professionals
- NIH Office of Dietary Supplements: Vitamin B12 fact sheet for consumers
- NICE NG239: Vitamin B12 deficiency in over 16s, diagnosis and management (2024)
- NHS: Vitamin B12 or folate deficiency anaemia, symptoms
- NHS: Vitamin B12 or folate deficiency anaemia, treatment
Sources checked 15 September 2026. This article is for general information and does not replace advice from your own doctor or pharmacist. See our editorial policy and medical disclaimer.
