Vitamin B12 Deficiency: Symptoms, Causes, Risks

Vitamin B12 deficiency can cause fatigue, muscle weakness, and memory problems

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Vitamin B12 deficiency is common, especially among vegetarians and older adults. Also known as cobalamin, it is a water-soluble vitamin found in meat, fish, and dairy.

Vitamin B12 is essential for brain and nerve function. A vitamin B12 deficiency can cause headaches, fatigue, muscle weakness, and depression. Low levels of vitamin B12 can be due to not getting enough vitamin B12 in your diet, or the body is unable to absorb it due to another medical condition.

Diagnosing vitamin B12 deficiency can be tricky because the symptoms are similar to other health conditions.  

This article looks at the symptoms, causes, and diagnosis of vitamin B12 deficiency. It also discusses treatment for vitamin B12 deficiency.

Symptoms of vitamin B12 deficiency
Verywell / Luyi Wang

Vitamin B12 Deficiency Symptoms

Vitamin B12 plays a complex role in your body. This is why B12 deficiency has so many potential symptoms.

There are four main categories of vitamin B12 complications. A complication is a problem caused by a medical condition or treatment.

These categories can cause a range of symptoms.

Complication of Vitamin B12 Deficiency Symptoms
Anemia, when you don't have enough red blood cells Fatigue, dizziness, paleness, and a rapid heart rate
Neuropathy, damage to the nerves Tingling, numbness, weakness, and balance problems
Myelopathy, damage to the spinal cord Sensory issues, numbness, tingling
Dementia, impairment of mental processes Cognitive decline and behavioral changes

Many of these symptoms are also found in other conditions. This is why it can be difficult to diagnose vitamin B12 deficiency.


Vitamin B12 plays a role in the production of red blood cells (RBCs). These cells carry oxygen through the body. Oxygen helps your body produce energy.

Vitamin B12 deficiency leads to defective RBCs. This causes anemia. Anemia can make you feel weak and fatigued.


Vitamin B12 is also a vital part of a healthy nervous system. Low B12 can cause the nerves in your brain, spinal cord, and elsewhere in your body to slowly degenerate.

This is called neuropathy, an impairment in nerve function. It causes weakness and imbalance. These symptoms can be worse if you also have anemia.


Myelopathy is an impairment of the spinal cord. It happens when neurons in part of the spinal cord deteriorate. Neurons are the cells that receive and process information from the outside world.

This results in muscle weakness. It can also cause difficulties in sensing light touch and vibration.

People with myelopathy may also have problems with proprioception. This is the ability to judge your body position, such as knowing how high you're holding up an arm without looking.

People with this condition may also have neuropathy-like symptoms.


Vitamin B12 deficiency may cause dementia. These symptoms may include:

  • Memory loss
  • Cognitive decline when the brain has difficulty with things like memory and judgment
  • Behavioral changes
  • Problems with self-care

Severe and long-term vitamin B12 deficiency can lead to psychosis. People with psychosis have a hard time telling the difference between what is real and what is not real.

Other Symptoms

Other symptoms of vitamin B12 deficiency may include:

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

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

What Causes Vitamin B12 Deficiency?

Vitamin B12 deficiency has two primary causes. Some people do not get enough B12 in their diet. Others have problems absorbing B12 in the intestines.

Inadequate Intake

Vitamin B12 is found in many food sources. These include:

  • Fish
  • Meat
  • Milk
  • Fortified cereals

Many sources of vitamin B12 come from animal proteins. Because of this, long-term vegetarians or vegans who don't take B12 supplements are at risk for vitamin B12 deficiency.

The risk is also higher in the elderly and people who abuse alcohol.

Impaired Absorption

Vitamin B12 is absorbed in the gut with the help of a protein called intrinsic factor. When the process of absorption doesn't work right, you may develop B12 deficiency.

Causes of impaired B12 absorption include:


The two primary causes of vitamin B12 deficiency are low B12 in the diet and problems with absorption.

Diagnosis of Vitamin B12 Deficiency

The diagnosis of vitamin B12 isn't always obvious. This is because many of the common symptoms overlap with those of other health conditions.

Your medical team may consider a number of diagnoses besides B12 deficiency.

History and Physical Examination

Your medical history can help your doctor understand your symptoms. A physical exam may also help identify the signs of B12 deficiency.

For example, a weak, rapid pulse or pale fingers may be a sign of anemia. Signs of neuropathy can include low sensation in your feet and poor reflexes. Confusion or trouble communicating are common signs of dementia.

Laboratory Tests

Laboratory tests can confirm your diagnosis. These tests include a complete blood count (CBC) and a vitamin B12 level.

B12 deficiency is associated with a particular type of anemia. This type, called macrocytic anemia, can be identified with a blood smear. With this type of anemia, RBCs are large and may have varied shapes and sizes.

Imaging and Specialized Tests

Other tests can be used to help confirm a diagnosis. These include nerve conduction studies, which measure the speed of the electrical signals in your nerves.

These tests can't confirm B12 deficiency on their own, though. This is why they are usually used alongside other diagnostic tools.


Diagnosis of B12 deficiency may include a physical exam, lab tests, and other specialized tests.

How Vitamin B12 Deficiency is Treated

Vitamin B12 deficiency can be managed with supplemental B12. This could be an oral supplement or an injection. If your B12 deficiency is caused by a problem with absorption, you may need an injection. The injection will help the vitamin absorb directly into your body.

Some patients need lifelong B12 supplementation. This usually depends on the cause of the deficiency. You may need to continue taking B12 supplements even after your symptoms improve.

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


You may have long-lasting symptoms even after treatment. Numbness, tingling, and weakness can impair your balance. A physical or occupational therapist can help you develop strategies to cope with these long-term problems.

Memory problems can improve as your vitamin B12 levels are corrected. Still, you may have some deficits in your thinking skills for a long time. Cognitive rehabilitation and therapy can help you improve your thinking and problem-solving skills.


Vitamin B12 deficiency can be hard to diagnose. Many of its symptoms can be confused with other conditions.

If you have a vitamin B12 deficiency, you may have symptoms of anemia, problems with your nerves, sensory issues, or even dementia. 

The two primary causes of B12 deficiency are low B12 levels in the diet and problems absorbing the vitamin. 

Vitamin B12 deficiency is diagnosed with a medical history, exam, laboratory tests, and other tests. It is usually treated with supplemental B12. 

You may need long-term rehabilitation after treatment. It may take a while for your symptoms to improve.

A Word From Verywell

Vitamin B12 deficiency can be a complicated diagnosis. This is because the effects and symptoms are so varied.

You might not have sudden symptoms of B12 deficiency. Instead, you may go through periods of gradual or intermittent declines in your vitamin B12 level. This can cause subtle or off-and-on symptoms.

If you have an inflammatory GI condition or if you have had gastric bypass, you may need preventive treatment. Regular vitamin B12 injections can help you avoid B12 deficiency.

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. This number goes up to almost 20% in adults over 60. 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.

  • What is the most common cause of vitamin B12 deficiency?

    The two most common causes of vitamin B12 deficiency is not consuming enough of the vitamin in your diet and an inability to absorb B12 in the intestines.

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Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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