What Is Vitamin B12 Deficiency?

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Vitamin B12 deficiency is a relatively common condition in children and adults. Besides a low dietary intake, other factors that may cause vitamin B12 deficiency include gastric bypass surgery and diseases associated with gastrointestinal (GI) malabsorption.

Diagnosing vitamin B12 deficiency can be tricky because there are so many symptoms that mimic those of other health conditions, including fatigue, muscle weakness, and cognitive difficulties.

Treatment generally entails taking a vitamin B12 supplement or getting the vitamin via injection. If you have an illness that predisposes you to vitamin B12 deficiency, managing the medical cause is also important.

Symptoms of vitamin B12 deficiency
Verywell / Luyi Wang

Vitamin B12 Deficiency Symptoms

Due to the complex and vast role vitamin B12 plays in the body, there are many potential symptoms.

Many symptoms stem from four main categories of vitamin B12-related complications:

Complication of Vitamin B12 Deficiency Symptoms
Anemia (red blood cell impairment) Fatigue, dizziness, paleness, and a rapid heart rate
Neuropathy (nerve degeneration) Tingling, numbness, weakness, and balance problems
Myelopathy (spinal cord impairment) Sensory issues, numbness, tingling
Dementia Cognitive decline and behavioral changes


Vitamin B12 plays a role in the production of red blood cells (RBCs), which normally carry oxygen throughout the body. Since oxygen is a vital part of your body's energy production, when RBCs are defective (which occurs with vitamin B12 deficiency), anemia develops.


Vitamin B12 is also a vital part of a healthy nervous system, and its absence causes slow degeneration of the nerves in the brain, spinal cord, and peripheral nerves. The weakness and imbalance associated with neuropathy—impairment in nerve function—can be exacerbated when anemia is also present.


Myelopathy, an impairment of spinal cord function, is produced when there is a deterioration of neurons in the posterior column of the spinal cord. This results in muscle weakness and deficits in detecting light touch, vibration, and proprioception (position sense). Some neuropathy-like symptoms are common as well.


Vitamin B12 deficiency may cause dementia, resulting in memory loss and cognitive decline, behavioral changes, and problems with self-care. With severe and chronic vitamin B12 deficiency, psychosis may develop.

Other Symptoms

Other symptoms and signs of vitamin B12 deficiency may include:

  • Low white blood cell count, which increases your risk for infection
  • Low platelet count, which increases your risk for bleeding
  • Headaches
  • Weight loss
  • Mood changes, especially depression
  • Behavioral changes
  • Walking problems
  • Loss or diminished sense of smell
  • Swollen tongue (called glossitis)

Symptoms of vitamin B12 deficiency typically develop gradually over the course of weeks or months and do not usually improve without treatment.


The two main causes of vitamin B12 deficiency are inadequate intake and impaired absorption in the intestines.

Inadequate Intake

Vitamin B12 is found in animal proteins such as fish, meat, and milk, as well as some fortified cereals. Longstanding vegetarians or vegans who don't use supplements may develop a B12 deficiency due to inadequate nutritional intake of the vitamin. People who abuse alcohol and the elderly are also at risk for vitamin B12 deficiency.

Impaired Absorption

Since vitamin B12 is absorbed in the gut through a complex process that relies on a protein called intrinsic factor, impaired intestinal absorption may also result in this vitamin deficiency.

Causes of impaired vitamin B12 gut absorption include:

  • Pernicious anemia, an autoimmune disorder in which antibodies attack the cells that release intrinsic factor
  • Inflammatory gastrointestinal (GI) disorders like Crohn's disease and celiac disease
  • Prolonged use of certain medications like metformin and proton pump inhibitors (PPIs)
  • Gastric bypass surgery, which involves resection of parts of the stomach and/or small intestine
  • GI resection surgery, which is a treatment for serious medical problems such as bowel obstruction or cancer


While the diagnosis of vitamin B12 may seem straightforward, it isn't always very obvious. This is because many of the common symptoms of vitamin B12 deficiency overlap with those of other health conditions.

Your medical team may consider a number of diagnoses in addition to vitamin B12 deficiency when working to explain your symptoms.

History and Physical Examination

Besides a medical history, which may reveal symptoms like unexplained fatigue or numbness and tingling, your physical examination may identify signs of vitamin B12 deficiency.

For example, a weak, rapid pulse or pale fingers may be a sign of anemia. Diminished sensation in your feet and decreased reflexes can be a sign of neuropathy. Lastly, confusion or difficulty communicating are common signs of dementia and depression.

Laboratory Tests

Laboratory tests, specifically a complete blood count (CBC) and a vitamin B12 level, can confirm a diagnosis of vitamin B12 deficiency.

Moreover, often with vitamin B12 deficiency, a specific type of anemia called macrocytic anemia (not to be confused with pernicious anemia) can be identified with a blood smear. The RBCs appear large and may have a varied shape and size.

Imaging and Specialized Tests

While certain imaging tests and nerve conduction studies (NCV) can be helpful in assessing the effects of vitamin B12 deficiency, they do not produce a specific pattern of results that corresponds with this deficiency. As such, if performed, results must be considered alongside other assessments.


Vitamin B12 deficiency can be managed with oral (by mouth) or intramuscular (IM) injections of the vitamin. If decreased absorption is among the causes of your vitamin B12 deficiency, you may need to have an injection so that it will be absorbed directly into your body.

If possible, the cause of the B12 deficiency should be addressed, especially if you have not had a surgical resection or do not know why you are low in this vitamin.

Depending on the reason for your vitamin deficiency, you may need to continue to use lifelong supplementation with vitamin B12 even after your symptoms improve.

Recovery from vitamin B12 deficiency takes time and you may not experience any improvement during the first few months of treatment. Improvement may be gradual and may continue for up to six to 12 months.


It is possible that you may continue to suffer from lasting deficits of vitamin B12 deficiency, such as numbness, tingling, and weakness. These effects can impair your balance. Working with a physical or occupational therapist may help you optimize your abilities despite these lingering problems.

In addition, memory problems can improve as your vitamin B12 levels are corrected, but you may continue to experience some deficits in cognitive (thinking) skills for a long time.

Cognitive rehabilitation and therapy is a challenging process, but it can help you maximize and improve your thinking and problem-solving skills.

A Word From Verywell

Vitamin B12 deficiency can be a fairly complicated diagnosis because the effects and symptoms are so varied. You might not experience sudden effects of the vitamin deficiency, but instead go through periods of gradual or intermittent declines in your vitamin B12 level that result in subtle or off-and-on symptoms.

If you have an inflammatory GI condition or if you have had a gastric resection, you may need to use a preventative treatment such as regularly scheduled vitamin B12 injections to avoid becoming deficient in this vitamin.

Frequently Asked Questions

  • What are normal B12 levels?

    Normal vitamin B12 levels are 160 to 950 picograms per milliliter (pg/mL) or 118 to 701 picomoles per liter (pmol/L).

  • Is vitamin B12 deficiency common?

    It's somewhat common. In the U.S., about 6% of adults under age 60 are deficient in B12, but almost 20% of adults over 60 are. Deficiency is more common in the elderly population because the ability to absorb B12 declines with age.

  • Do medication interactions impact B12 levels?

    Yes, there are several medications that may interact with B12 and result in poor absorption. These include acid-reducing drugs (histamine 2-receptor antagonists and proton pump inhibitors) and metformin.

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