Testing · 29 October 2026 · 8 min read

Vitamin B12 deficiency: symptoms, causes and testing

Vitamin B12 deficiency develops slowly and can look like tiredness, forgetfulness or just getting older. The body stores B12 in the liver, sometimes for a few years, so symptoms can appear long after intake or absorption has dropped. Because nerve damage can be permanent if it goes untreated, numbness, tingling or balance problems deserve a clinician's attention. A blood test can check your level, and treatment depends on the cause.

Illustration of a fish, two eggs, a milk carton and a plant-based drink carton with a leaf label

In short

B12 is found naturally in animal foods such as fish, meat, poultry, eggs and dairy. It is not present in plant foods unless they are fortified.
People at higher risk include those who follow a strict vegetarian or vegan diet, older adults, and people with stomach or intestinal surgery, pernicious anemia, celiac or Crohn disease, or long-term metformin or acid-reducing medicine use.
Low B12 can cause anemia, numbness and tingling, weakness, loss of balance and memory problems. Nerve symptoms can appear even without anemia.
The first test is a blood B12 level, usually with a complete blood count. A methylmalonic acid (MMA) test can confirm a true deficiency.
Treatment depends on the cause: pills for a diet-related shortfall, and shots or high-dose supplements when absorption is the problem.

What B12 does

Vitamin B12 helps form red blood cells and supports protein metabolism and the nervous system. Absorption depends on intrinsic factor, a substance made in the stomach. Because the liver stores B12, sometimes for a few years, a deficiency can build for a long time before symptoms show.

The best way to meet your B12 needs, according to MedlinePlus, is to eat a wide variety of animal products. Fortified cereals and some nutritional yeasts can help people who do not eat animal foods.

Symptoms of deficiency

Fatigue or extreme tiredness, pale skin and shortness of breath on exertion, as in other types of anemia.
Numbness, tingling or pins and needles in the hands and feet.
Weakness and loss of balance.
Memory problems, confusion or changes in mood.
A sore, red tongue and mouth ulcers.
Vision problems.

The NHS notes that some of these problems can occur without anemia, so a normal blood count does not rule out low B12 when you have nerve symptoms. It also warns that some problems caused by the deficiency can be irreversible, which is why early diagnosis matters.

Who is at higher risk

Vegans and strict vegetarians, particularly without supplements or fortified foods.
People over 50, among whom deficiency is most common.
People taking metformin or proton pump inhibitors, which can reduce B12 levels, or using antacids for a long time.
People who have had stomach surgery, such as a gastrectomy, or small intestine surgery.
People with pernicious anemia, an autoimmune condition in which the body destroys the stomach cells that make intrinsic factor.
People with celiac disease or Crohn disease, which can interfere with absorption.
Pregnant people, who are listed among higher-risk groups for low levels.

How a clinician checks B12

A clinician usually orders a complete blood count and a serum vitamin B12 level. MedlinePlus says the B12 level test is most often done when other blood tests suggest megaloblastic anemia or when there are nerve symptoms. You may be asked to fast for about 6 to 8 hours, and some medicines, including metformin and proton pump inhibitors, can affect the result, so ask before you stop any.

A deficiency should be confirmed by measuring methylmalonic acid, which is raised in true B12 deficiency. If a deficiency is found, further tests may look for the cause, including pernicious anemia. Your clinician explains what your own numbers mean. If you have already started taking B12, say so, because it can change the result.

Folic acid can hide the problem

Folic acid can mask a B12 deficiency while the nerve effects of low B12 continue. For that reason the NHS says a clinician checks your B12 level before starting folic acid. Do not start folic acid on your own if the cause of anemia is unclear.

Treatment in general terms

Diet-related deficiency: daily B12 tablets can resolve the problem. The NHS says vegans may need tablets lifelong.
Absorption problems such as pernicious anemia, or after stomach or intestinal surgery: B12 shots are often used and may be needed for life. Some people can use high-dose oral supplements, and a nasal form exists.
Follow-up: a clinician repeats blood tests to see whether treatment is working.

The type and schedule are your clinician's decision and depend on the cause. Excess B12 is usually passed out in urine, but there is no reason to take large amounts without a clinician's advice.

When to see a doctor, and red flags

See a clinician if you have lasting tiredness, numbness or tingling in the hands or feet, memory changes or a sore tongue, especially if you eat a plant-based diet, take metformin or acid-reducing medicine long term, have had stomach or bowel surgery, or have an autoimmune condition. Bring a list of every medicine and supplement you take, including B-vitamin complexes.

Red flags: call 911 for sudden weakness or numbness on one side of the body or face, sudden trouble speaking or seeing, or confusion. Get prompt medical care for numbness and weakness that is getting worse, trouble with balance or walking, fainting, or a racing heartbeat with breathlessness.

Questions to ask your clinician

Do my diet and medicines mean I should be tested for B12?
If my result is borderline, should I have a second test such as MMA?
Which form of treatment suits me: tablets, shots or another option?
How long will I need treatment, and when will you recheck my levels?
Should we look for a cause of poor absorption?

Questions and answers

Do vegetarians who eat eggs and dairy get enough B12?

Eggs and dairy do contain B12, so some do. It depends on how much you eat, so ask about testing if you have symptoms or a limited diet.

Are pills or shots better?

It depends on why the level is low. Pills usually work for a diet-related shortfall, while shots are often used when the body cannot absorb B12 properly.

Can you take too much B12?

Extra B12 is usually removed in the urine, but high amounts are rarely needed. Ask your clinician before choosing a dose.

Should I be checked for B12 if I take metformin?

Long-term metformin use is linked with lower B12, so it is reasonable to ask how often you should be tested, especially if you notice tingling or unusual tiredness.

Can I have low B12 with a normal blood count?

Yes. Nerve symptoms can show up without anemia, so numbness or poor balance still deserves a B12 check.

Sources

Sources checked on 29 October 2026.