Vitamin B12 Deficiency: Causes, Symptoms & Risk Factors
Vitamin B12 deficiency can affect your energy, nerves, and concentration. Discover what causes low B12, who’s most at risk, how to recognize the symptoms, and why early diagnosis matters for preventing long-term nerve damage.
Key takeaways
- Vitamin B12 deficiency has two main causes: not getting enough B12 or having difficulty absorbing it.
- Symptoms can affect the blood and nervous system. Fatigue, weakness, tingling, numbness and balance problems are possible signs.
- You can develop a deficiency even if you eat animal foods. Certain digestive conditions, medications and autoimmune disorders affect B12 absorption.
- Neurological symptoms can appear without anemia. A normal blood count does not completely exclude B12 deficiency.
- Diagnosis and treatment depend on the cause. Blood tests and medical assessment help determine whether oral supplements, injections or additional investigations are appropriate.
In this article
Do you feel tired even after getting enough sleep? Maybe you’ve noticed that concentrating has become harder or that you sometimes experience tingling in your hands and feet. These symptoms can have many causes, and vitamin B12 deficiency is one possibility.
Vitamin B12 helps your body make healthy red blood cells and supports normal nervous-system function. When your body doesn’t get or absorb enough of it, the effects may develop gradually, sometimes without obvious warning signs.
So what causes vitamin B12 deficiency, who is more likely to develop it, and how can you tell whether low B12 is actually responsible for your symptoms?
What Is Vitamin B12 Deficiency?
Vitamin B12, also called cobalamin, helps your body form healthy red blood cells, produce DNA and maintain normal nerve function.
It is one of the 13 essential vitamins your body needs but cannot produce in sufficient amounts on its own.
Vitamin B12 deficiency develops when the body does not have enough of this nutrient to maintain its normal functions. This may happen because dietary intake is inadequate, absorption is impaired or both.
Your liver stores vitamin B12, which allows the body to maintain a supply even when intake becomes insufficient. Because of these stores, deficiency may take months or years to develop, although the timing varies according to the cause and individual circumstances.[1][3]
A deficiency does not always begin with anemia. In some people, neurological symptoms may appear before changes in red blood cells become obvious.
What Causes Vitamin B12 Deficiency?
There are two main reasons your body may develop a B12 deficiency: an inadequate supply from food or difficulty absorbing the vitamin. Several medical conditions and medications can contribute to the second problem.
1. Not Getting Enough Vitamin B12 From Food
Vitamin B12 occurs naturally in animal-derived foods, including meat, fish, seafood, eggs and dairy products. People who exclude these foods need reliable alternative sources.
Fortified breakfast cereals, certain plant-based drinks and fortified nutritional yeast may provide B12, depending on the product. Ordinary unfortified plant foods are not reliable sources.[1]
Our guide to B vitamins in food compares dietary sources, including options for people following plant-based diets.
For people following a vegan diet, regular B12 intake from suitable fortified foods, supplements or both is important. Relying on occasional fortified products without checking their B12 content may not provide a consistent supply.
2. Problems Absorbing Vitamin B12
Vitamin B12 absorption involves several steps in the digestive system. The vitamin in food is usually attached to proteins and must first be released during digestion.
Stomach acid and digestive enzymes help release B12 from food. A protein called intrinsic factor, produced by cells in the stomach, then binds to the vitamin. This complex is absorbed primarily in the last part of the small intestine, called the terminal ileum.[1]
If any important part of this process is disrupted, someone may eat enough B12 but still develop a deficiency.
Conditions affecting the stomach or small intestine, including certain digestive diseases and surgeries, can interfere with absorption. You can read more about the general process in our guide to how vitamin absorption works.
3. Pernicious Anemia and Autoimmune Gastritis
Pernicious anemia is associated with autoimmune processes that interfere with vitamin B12 absorption, typically through reduced intrinsic factor availability.
In autoimmune gastritis, the immune system damages stomach cells involved in producing acid and intrinsic factor. This can make normal B12 absorption difficult or impossible.
Simply eating more B12-rich foods may not correct a deficiency caused by this problem. Diagnosis and appropriate treatment are important, and some people need lifelong B12 replacement.[2][7]
4. Certain Medications
Some medications can contribute to reduced B12 levels, particularly with long-term use.
Examples include metformin, which is commonly prescribed for type 2 diabetes, and proton pump inhibitors such as omeprazole, which reduce stomach acid.[4]
Not everyone taking these medicines will develop a deficiency. The potential effect depends on factors including treatment duration, diet and medical history.
Do not stop prescribed medication because of a concern about B12. Ask your healthcare professional whether monitoring is appropriate for your situation.
What Are the Symptoms of Vitamin B12 Deficiency?
Vitamin B12 deficiency can affect people differently. Some notice persistent tiredness or weakness, while others experience changes in sensation, balance, memory or concentration.
The following symptoms can occur with B12 deficiency, but none is specific enough to establish a diagnosis on its own.
| Symptom | What You Might Notice |
|---|---|
| Fatigue and weakness | Everyday activities feel more exhausting than usual |
| Shortness of breath during activity | You become breathless or tired more quickly when walking or climbing stairs |
| Tingling or numbness | Pins and needles or reduced sensation in your hands and feet |
| Balance problems | You feel unsteady when walking or have difficulty coordinating movements |
| Difficulty concentrating | Following conversations, remembering information or focusing becomes harder |
| A red or sore tongue | Your tongue appears inflamed or feels uncomfortable |
| Mood changes | Irritability, low mood or depressive symptoms |
Symptoms Related to Anemia
Vitamin B12 is necessary for normal red blood cell formation. When a deficiency causes megaloblastic anemia, the body may have difficulty producing healthy red blood cells.
This can contribute to fatigue, weakness, paleness, dizziness or shortness of breath, especially during physical activity.[1][2]
However, fatigue is a general symptom with many possible causes. Feeling tired does not automatically mean that vitamin B12 is low.
Neurological Symptoms Can Occur Without Anemia
Vitamin B12 also supports the nervous system, including the maintenance of myelin, the protective covering around many nerve fibers.
A deficiency can lead to neurological problems even when a person does not have anemia or obvious changes in their complete blood count.
Persistent tingling, numbness, changes in walking or balance, or unexplained cognitive changes should be medically evaluated. Delayed treatment can sometimes result in neurological damage that does not fully recover.[3][7]
Sudden weakness, sudden difficulty speaking or a sudden loss of balance may indicate another urgent medical condition and should not be assumed to result from vitamin deficiency.
Who Is Most at Risk?
Several groups have an increased likelihood of developing B12 deficiency because of dietary habits, age, digestive conditions or medication use.
- Vegans and some vegetarians: Especially those without consistent B12 intake from fortified foods or supplements.
- Older adults: Reduced stomach acid or changes in digestive health can make it harder to release and absorb B12 from food.
- People with autoimmune gastritis or pernicious anemia: These conditions interfere with intrinsic factor and normal absorption.
- People with certain digestive diseases: Conditions affecting the stomach or small intestine, including Crohn’s disease and celiac disease, may increase risk.
- People who have had digestive surgery: Procedures involving the stomach or terminal ileum can reduce B12 absorption.
- People using certain medicines long-term: Metformin and some acid-reducing medications can affect B12 status.
Having a risk factor does not mean that you are deficient. However, diet, medical history and symptoms can help a healthcare professional determine whether testing is appropriate.[1][7]
How Is Vitamin B12 Deficiency Diagnosed and Treated?
Diagnosing B12 deficiency involves more than identifying one symptom or interpreting a blood test in isolation. Healthcare professionals consider the person’s symptoms, dietary intake, medical history, medications and laboratory results.
How Is Vitamin B12 Deficiency Diagnosed?
A clinician may recommend blood tests to measure vitamin B12 and assess the possible effects of deficiency.
Common investigations include:
- Vitamin B12 blood test: Measures the amount of B12 in the blood. The result must be interpreted using laboratory reference ranges and the clinical situation.
- Complete blood count (CBC): Evaluates red blood cells and may reveal anemia or changes in red blood cell size.
- Methylmalonic acid (MMA): May help clarify B12 status when an initial result is borderline or does not fully explain symptoms.
- Additional tests: Depending on the situation, clinicians may investigate folate status, autoimmune gastritis or other causes of impaired absorption.
A B12 result near the lower end of the reference range can sometimes be difficult to interpret. An additional MMA test may be useful, but MMA can also increase when kidney function is reduced, so it is not interpreted independently of other information.[1][7]
A normal complete blood count does not exclude every B12 deficiency, particularly when neurological symptoms are present.
Another important consideration is vitamin B9 (folate). Folate deficiency can produce a similar type of anemia, and the two conditions may require different treatment approaches.
When testing is needed, it is generally useful to discuss it before starting B12 supplements, because supplementation may change laboratory results. However, when significant neurological involvement is suspected, medical treatment should not be delayed merely to obtain routine test results.[7]
How Is Vitamin B12 Deficiency Treated?
Treatment aims to restore adequate B12 levels and address the underlying cause of the deficiency. The appropriate approach depends on dietary intake, absorption problems, severity and whether neurological symptoms are present.
Some people can be treated with oral B12 supplements. Others may require injections, particularly when there are serious neurological symptoms or certain conditions that significantly affect absorption.
High-dose oral B12 can also be appropriate in some cases of impaired absorption, depending on the diagnosis and clinical guidance. Having a digestive condition does not automatically mean that injections are the only effective treatment.[1][7]
When an underlying cause is permanent, such as autoimmune gastritis, lifelong replacement treatment may be necessary.
Symptoms may begin improving after treatment starts, but recovery varies. Blood-related changes can improve before some neurological symptoms, and longstanding nerve damage may not completely reverse.
Vitamin B12 treatment corrects a deficiency; it is not a general energy booster for people whose B12 status is already adequate. Our article Do B Vitamins Give You Energy? explains this difference.
What This Means in Practice
If you’re wondering whether you get enough B12, start by considering your usual diet, your health history and any symptoms that have developed.
- If you follow a vegan diet: Make sure you have a reliable and regular source of vitamin B12 from fortified foods, supplements or both.
- If you take metformin or stomach-acid-reducing medicines: Ask whether B12 monitoring is appropriate, especially when symptoms or other risk factors are present.
- If you experience persistent tingling, numbness or balance problems: Seek medical assessment promptly rather than assuming the symptoms are harmless.
- If you feel constantly tired: Remember that B12 deficiency is only one possible cause and that testing may be more useful than trying multiple supplements.
- If you’re receiving B12 treatment: Follow the recommended schedule and discuss symptoms that continue or worsen.
If supplements are recommended, dose and administration instructions depend on why you need them. For general information about avoiding overlapping products and understanding supplementation, see how to take B vitamins.
The goal is to identify and address the cause of the deficiency, rather than taking increasingly high amounts without understanding what your body needs.
Frequently asked questions
How Soon Will You Feel Better After B12 Treatment?
Some people notice improvement within a few weeks, while others need longer. Recovery depends on the severity and duration of the deficiency and the symptoms involved. Neurological symptoms can improve more slowly, and some may persist after treatment. If symptoms continue, worsen or new problems appear, follow up with your healthcare professional rather than assuming recovery will happen on a fixed schedule.
Is Vitamin B12 Deficiency the Same as Folate Deficiency?
No. Vitamin B12 and folate are different nutrients, although deficiency in either can cause megaloblastic anemia. An important difference is that B12 deficiency may also produce neurological problems. High folic acid intake can improve anemia without correcting neurological damage caused by low B12. Our guide to folate vs. folic acid explains their differences and nutritional roles.
Can a Normal B12 Blood Test Miss a Deficiency?
Sometimes. Results close to the diagnostic threshold may be difficult to interpret, and no single test is appropriate for every clinical situation. If symptoms and risk factors suggest B12 deficiency, a healthcare professional may consider further investigation, including MMA or tests related to the underlying cause. A normal blood count does not necessarily rule out neurological involvement.
Final thoughts
Vitamin B12 deficiency isn’t always caused by eating too few B12-rich foods. Sometimes, the problem is that the body cannot absorb the vitamin effectively, even when the diet provides sufficient amounts.
Fatigue may be one sign, but tingling, numbness and balance problems also deserve attention, particularly because neurological symptoms can develop without anemia. Identifying the underlying cause and starting appropriate treatment can help reduce the risk of lasting complications.
References
- National Institutes of Health, Office of Dietary Supplements. Vitamin B12: Fact Sheet for Health Professionals. NIH ODS.
- National Health Service (NHS). Vitamin B12 or Folate Deficiency Anaemia. NHS.
- Shipton MJ, Thachil J. Vitamin B12 Deficiency — A 21st Century Perspective. Clinical Medicine, 2015. PubMed Central.
- Miller JW. Proton Pump Inhibitors, H2-Receptor Antagonists, Metformin, and Vitamin B12 Deficiency: Clinical Implications. Advances in Nutrition, 2018. PubMed Central.
- National Institutes of Health, Office of Dietary Supplements. Vitamin B12: Fact Sheet for Consumers. NIH ODS.
- Mayo Clinic. Vitamin B12 Injections. Mayo Clinic.
- National Institute for Health and Care Excellence (NICE). Vitamin B12 Deficiency in Over 16s: Diagnosis and Management. NICE Guideline NG239, 2024. NICE.
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