Vitamin B12 Deficiency: Signs, Causes and Treatments | Ada (2024)

What is vitamin B12 deficiency?

Vitamin B12 deficiency occurs when there are inadequate levels of the vitamin B12 in the body. This important vitamin is necessary for the production of red blood cells and the healthy functioning of the nervous system.

A lack of vitamin B12 can cause anemia and other health problems. 1 2 Anemia is a condition where the body either cannot make enough healthy red blood cells or cannot produce enough of the substance hemoglobin that allows red blood cells to transport oxygen around the body.

There are several different types of anemia, each with their own causes and symptoms. For example, vitamin B12 deficiency can cause megaloblastic anemia, a condition where the red blood cells are larger than normal and cannot function properly. 2 3

For many people, a balanced and varied diet provides all the vitamin B12 they need. 2 Good sources of vitamin B12 include meat, fish, eggs and dairy products.

Despite the availability of vitamin B12 in a balanced diet, deficiency is not all that uncommon, particularly among people over 50 years of age, premenopausal women and people who follow strict vegan diets. 4 5

Low levels of vitamin B12 may be the result of a number of different factors and conditions. One of the most common causes of vitamin B12 deficiency is pernicious anemia, a condition where a person’s immune system mistakenly reduces their ability to absorb the vitamin. Less common causes of deficiency include conditions affecting the stomach or intestines that interfere with absorption of vitamin B12, inadequate dietary intake, and certain medications. 1 6

Symptoms of vitamin B12 deficiency usually develop gradually and can be wide-ranging. These may include general symptoms of [anemia]((/conditions/anemia/), such as fatigue and lethargy, as well as the symptoms specific to the deficiency, such as yellow tinge to the skin and a sore tongue.

If left untreated, the symptoms of vitamin B12 deficiency tend to worsen and irreversible problems involving the nerves and brain may develop. The risk of experiencing a number of serious complications, including heart failure, may also increase. 3 7 For this reason, it is important to seek medical advice without delay should any of these symptoms be present.

Symptoms of Vitamin B12 deficiency

A person with vitamin B12 deficiency may notice general symptoms of anemia as well as symptoms that are more specific to the condition.

Symptoms more specific to a vitamin B12 deficiency include: 2 8 7 9

  • Pale yellow skin color
  • Painful, red tongue
  • Mouth ulcers and canker sores
  • Constipation
  • Pins and needles, numbness or other strange sensations in the hands, legs or feet
  • Vision disturbances
  • Difficulty walking and balance problems
  • Perceptible differences in mood, thoughts, feelings and behavior
  • Confusion and difficulty thinking. In severe cases, dementia
  • Memory loss
  • Irritability
  • Depression
  • Psychosis 3

The symptoms of vitamin B12 deficiency can develop slowly and worsen over time. Some symptoms may be experienced by people who have a vitamin B12 deficiency without anemia. Some people may experience no symptoms, despite low levels of vitamin B12. 7

Because of the wide range of possible symptoms, many of which can also occur as a result of other conditions, vitamin B12 deficiency may not be recognized immediately. 9 If a person has any reason to suspect the condition, it is important that they inform their healthcare practitioner.

In babies, signs of vitamin B12 deficiency may include failure to thrive, movement difficulties, delays in reaching developmental milestones, and anemia. 8

General symptoms caused by anemia

A person with vitamin B12 deficiency may also notice general symptoms of anemia. Symptoms that are commonly experienced in anemia, regardless of the cause, include the following: 7

  • Fatigue
  • Lethargy
  • Breathlessness
  • Faintness
  • Headaches

Less common symptoms of anemia may include: 2

  • Paleness
  • Palpitations
  • Tinnitus (ringing in the ears)
  • Loss of appetite
  • Altered sense of taste
  • Unexplained weight loss

Ada can help you check your symptoms. Download the free Ada app to begin your personal health assessment.

What causes vitamin B12 deficiency?

Pernicious anemia is a common cause of vitamin B12 deficiency. There are several other possible causes of the deficiency, but they tend to be less common. 2

Pernicious anemia

In order for vitamin B12 to be absorbed by the body, it needs to be combined with a protein called intrinsic factor in the stomach. This protein is produced by cells in the stomach lining. In people with pernicious anemia, the body’s immune system mistakenly attacks these cells, preventing intrinsic factor from combining with vitamin B12 and hampering its absorption. 2 7

Pernicious anemia is an autoimmune condition that most commonly affects people over 50 years old, and women seem to be more likely to develop it. Pernicious anemia is thought to run in families and seems to affect people who have other autoimmune conditions, such as Hashimoto’s thyroiditis and Addison’s disease, more often than those who do not. A healthcare practitioner can order a blood test to check for pernicious anemia. 2 7

Conditions affecting the stomach and intestines

People who have certain conditions that affect the stomach and intestines, or have had certain types of surgery, may be at risk of vitamin B12 deficiency. 2 7 10

  • Stomach conditions. Atrophic gastritis, which causes thinning of the stomach lining, infection with Helicobacter pylori bacteria, and a genetic condition that causes a lack of intrinsic factor can all cause vitamin B12 deficiency.
  • Intestinal conditions. Crohn’s disease, a condition that causes inflammation of the lining of the digestive tract, celiac disease, 8 chronic tropical sprue and a number of other conditions may lead to vitamin B12 deficiency.
  • Surgery. Surgical procedures that remove part or all of the stomach, or the end of the small intestine, may prevent adequate absorption of vitamin B12.


Some medicines can interfere with the absorption of vitamin B12, potentially leading to a deficiency if precautions are not taken. Metformin, a medicine commonly prescribed for diabetes, is one example. Others include neomycin, chloramphenicol, 8 colchicine and certain anticonvulsant drugs. 2

In addition, the long-term use of certain medicines that are used to treat stomach conditions, such as heartburn and peptic ulcers, 11 can worsen an existing vitamin B12 deficiency, but do not cause it. Examples of these drugs include proton pump inhibitors (PPIs) and H2 blockers. 2 7

Good to know: People taking any of these types of medication should discuss concerns about vitamin B12 deficiency with their healthcare practitioner.

Inadequate dietary intake

Though fairly uncommon, some people may develop vitamin B12 deficiency as a result of low levels in their daily diet. A balanced diet typically provides sufficient vitamin B12; however, strict vegans and people with a poor diet are at higher risk of developing a deficiency. 2 7 Good sources of vitamin B12 include:

  • Meat
  • Fish
  • Eggs
  • Dairy products

In addition, some breakfast cereals, soy products and other foods are fortified with vitamin B12. Fruit and vegetable products do not contain vitamin B12, unless they have been specially fortified. 1 8

In healthy people, the body tends to have a store of vitamin B12 that can last two to five years without being replenished. As a result, a deficiency may take several years to develop. 7 12

It is important that people making long-term dietary changes, for example becoming vegan, eat food products that have been fortified with vitamin B12 or take a supplement to reduce the risk of developing a deficiency. 9

Diagnosis of vitamin B12 deficiency

A doctor will typically take the person’s medical history and perform a physical examination.

If they suspect a vitamin B12 deficiency, they will usually request blood tests to be done. These tests can measure levels of vitamin B12 and folic acid, as well as the size and concentration of hemoglobin within the person’s red blood cells. 7

Drawbacks of blood tests for vitamin B12 deficiency

Some people experience symptoms of vitamin B12 deficiency despite their blood tests indicating normal levels. The test measures the total amount of the vitamin in the blood, but not all of it can necessarily be used by the body. 7 In addition, the range of normal levels may differ between laboratories. 13

For these reasons, healthcare practitioners will usually consider signs and symptoms, as well as the results of the blood tests when diagnosing vitamin B12 deficiency. 13

Read more about Blood Test Results »

Tests to identify the cause

If vitamin B12 deficiency is suspected or confirmed, further tests may be required to identify the cause. This will help to determine the recommended course of treatment. These investigations may include further blood tests for pernicious anemia 7 and other conditions.

Some people may be referred to specialists for further tests or treatment. These include hematologists, doctors specializing in blood conditions, and gastroenterologists, doctors specializing in the digestive system. 1

Ruling out folate deficiency

A deficiency of folate, the nutrient also known as folic acid or vitamin B9, good sources of which include foods like broccoli, asparagus, peas and brown rice, can cause some of the same symptoms as vitamin B12 deficiency. 7 For this reason, a doctor will typically examine the levels of folate in blood tests when checking for vitamin B12 deficiency. 3

Taking a lot of folic acid can mask the symptoms of a vitamin B12 deficiency, so in cases where folate deficiency is suspected, a doctor will usually test for vitamin B12 deficiency before prescribing medication. 12

Read more about Folate Deficiency »

Functional vitamin B12 deficiency

Sometimes blood tests will show normal serum levels of vitamin B12, but a person may experience symptoms and complications related to a deficiency. This can be known as fuctional vitamin B12 deficiency. In these cases, there may be an issue with the processing of vitamin B12 in the body.

Like most other cases of vitamin B12 deficiency, the condition can be treated with high doses of vitamin B12. 7 14 However, a prolonged functional vitamin B12 deficiency can lead to the same problems as a regular vitamin B12 deficiency.

Treatment of Vitamin B12 deficiency

Treatment will depend on the reasons for the vitamin B12 deficiency. In most cases, having injections or taking a prescribed oral supplement will be sufficient to treat the condition. 7

A doctor may recommend having high-dose injections of vitamin B12, usually in a form called hydroxocobalamin, every second day for two weeks, or until symptoms have cleared.

If the cause of the deficiency is dietary, the doctor may advise taking a daily supplement or continuing to have injections twice a year or more, indefinitely. 7 They may also refer the person to a dietician for advice on ways to increase vitamin B12 intake in their diet. 1 3

In cases where the deficiency is not related to a person’s diet, it will usually be necessary to have vitamin B12 injections every three months or more frequently, for the rest of their life. 7

People who have symptoms that affect their nervous system, such as pins and needles or numbness, may be referred to a hematologist for specialized management of the deficiency. It may be necessary for them to have injections every two months or more frequently, for life. 2 7

Vitamin B12 injections typically do not have any side-effects other than a small amount of discomfort where the needle is inserted. 2

Follow-up blood tests will generally be requested one to three months after starting treatment, to check that vitamin B12 levels have returned to normal. Thereafter, a doctor may advise a once-yearly follow-up test. 7 3 12

In most cases, a vitamin B12 deficiency is easy to treat and complications are rare. 1 However, in some cases, particularly where there has been a severe or prolonged deficiency, nerve damage may be permanent and irreversible. 2 3

Good to know: Over-the-counter supplements do not usually contain adequate amounts of vitamin B12 to correct a deficiency. 11

Prevention of vitamin B12 deficiency

While it may not be possible to prevent vitamin B12 deficiency in all cases, steps can be taken to reduce the likelihood of the condition developing.

A person should speak to their healthcare practitioner about getting their vitamin B12 levels checked periodically if they: 9

  • Use a proton pump inhibitor on a long-term basis
  • Use an H2 blocker on a long-term basis
  • Take metformin for their diabetes
  • Are strict vegans
  • Have conditions affecting the stomach
  • Have had gastric surgery or surgery on the small intestine

People with conditions that may interfere with the absorption of the vitamin, such as celiac disease and Crohn’s disease, as well as those over the age of 50, should also discuss their vitamin B12 needs with a healthcare practitioner. 9

It is recommended that strict vegans (and sometimes vegetarians) and people over 50 include breads, cereals or other food products that have been fortified with vitamin B12 in their diet, and/or take a supplement. 9

Complications of vitamin B12 deficiency

Occasionally, a vitamin B12 deficiency can cause complications. These depend on the severity and duration of the deficiency, but may include: 7 3

  • Neurological problems. These may include vision disturbances, memory loss, pins and needles, difficulty walking or speaking, and damage to the nerves (peripheral neuropathy), particularly in the legs. Occasionally, some of these problems may be irreversible.
  • Infertility. A vitamin B12 deficiency may cause women to be unable to fall pregnant. However, this is usually reversible with treatment.
  • Stomach cancer. In cases of vitamin B12 deficiency caused by pernicious anemia, the risk of developing stomach cancer may be increased.
  • Neural tube defects. Pregnant women with a vitamin B12 deficiency may be at an increased risk of their baby developing serious birth defects such as spina bifida.

In addition, anemia of all kinds can sometimes cause serious heart and lung complications. These include a fast heartbeat and heart failure. 3

Read more about anemia complications »

To prevent complications, people who suspect they may have a vitamin B12 deficiency are advised to consult a qualified healthcare practitioner without delay.

Other names for vitamin B12 deficiency

  • Cobalamin deficiency

Vitamin B12 deficiency FAQs

Q: Are vegetarians and vegans at risk of vitamin B12 deficiency?
A: Yes. Vitamin B12 is found in animal products like meat, fish and dairy, but not plant products, meaning that people following a vegan or vegetarian diet are at an increased risk of developing a vitamin B12 deficiency due to inadequate dietary intake. 4 7 To minimize the likelihood of a deficiency, it is recommended that strict vegans and vegetarians include foods that have been fortified with vitamin B12 in their daily diet. Examples include certain breads, soy products and cereals, as well as certain yeast extracts. It may also be necessary to take a daily supplement.

Q: Can vitamin B12 deficiency cause depression?
A: Yes. A vitamin B12 deficiency can cause a wide range of symptoms, including psychiatric symptoms like irritability, psychosis and depression. 3 It is important to remember that depression can be caused by a number of different factors. If a person suspects that a vitamin B12 deficiency may be implicated in their depressed mood, they are advised to speak to a healthcare practitioner.

Check your symptoms with the free Ada app.

Q: Is there a link between alcohol and vitamin B12 deficiency?
A: Yes. Research shows that even moderate alcohol consumption may decrease vitamin B12 levels, and alcoholics are thought to be at risk of vitamin B12 deficiency. In some cases, blood tests may show falsely high levels of vitamin B12; this confusing status can be caused by alcoholic liver disease and may mask a functional vitamin B12 deficiency. 15 16 17

Vitamin B12 Deficiency: Signs, Causes and Treatments | Ada (2024)
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