An Overview of Vitamin B12 Deficiency

This vitamin impacts many parts of your body

In This Article

Vitamin B12 deficiency is relatively common and can affect children and adults of all ages. Most of the time this vitamin deficiency is mild and the effects can be subtle. There are some predisposing factors that lead to vitamin B12 deficiency, such as gastric bypass surgery and gastrointestinal (GI) malabsorption, but low dietary intake can cause it as well.

Diagnosing vitamin B12 deficiency can be tricky because there are so many effects. Blood tests can be used to identify a vitamin B12 deficiency as well as some of the effects, such as anemia

Treatment generally includes either getting enough vitamin B12 in your diet or using a supplement. If you have an illness that predisposes you to vitamin B12 deficiency, then managing the medical cause is also important.


There are a number of effects of vitamin B12 deficiency, and the symptoms can vary. Typically, symptoms gradually develop over the course of weeks or months and do not usually improve without treatment.

Common effects of mild or recent vitamin B12 deficiency include:

  • Fatigue
  • Headaches
  • Dizziness
  • Weight loss

After a while, vitamin B12 deficiency can cause more substantial effects, producing vague symptoms. Effects of severe or long-standing vitamin B12 deficiency include:

  • Tingling and/or numbness of the fingers and toes
  • Impaired balance
  • Mood changes, especially depression
  • Muscle weakness
  • Diminished memory
  • Problems with bowel or bladder control
  • Behavioral changes
  • Sore mouth or tongue
  • A rapid heart rate

These symptoms stem from a number of different effects of vitamin B12 deficiency, and you can have any combination of effects from this condition.

Physical effects of vitamin B12 deficiency and their symptoms include:

  • Anemia, which is a deficiency of red blood cell function, causes fatigue, and may also predispose you to a rapid heart rate.
  • Neuropathy, which is impairment in nerve function, can cause tingling, numbness, weakness, and balance problems. Anemia can exacerbate the weakness and imbalance.
  • 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). Numbness and tingling are common effects of myelopathy as well.
  • Dementia can have many causes and vitamin b12 deficiency contributes to dementia, resulting in memory loss, behavioral changes, and problems with self-care.


Vitamin B12 is a natural component of in animal proteins such as meat and milk, and some grains are supplemented with vitamin B12. Longstanding vegetarians or vegans who don't use supplements may develop a B12 deficiency due to inadequate nutritional intake of the vitamin.

But the problem can also result from impaired intestinal absorption. The vitamin is absorbed in the small intestine through a complex process that relies on a protein called intrinsic factor, which is secreted from the stomach.

Causes of diminished vitamin B12 alabsorption include:

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

Vitamin B12 plays a role in the production of red blood cells (RBCs). RBCs carry oxygen and carbon dioxide throughout the body. Oxygen is a vital part of your body's energy production, and when RBCs are defective, which occurs with vitamin B12 deficiency, you can become low in energy.

This vitamin 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, causing many of the effects of vitamin B12 deficiency.


The diagnosis of vitamin B12 can seem straightforward, but it isn't always very obvious. All of the common symptoms and effects, such as fatigue and neuropathy, have other causes, so your medical team may consider a number of possibilities to explain your symptoms—not just vitamin B12 deficiency.

In general, 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 can be a sign of neuropathy or myelopathy. Decreased reflexes are usually a sign of neuropathy. And confusion or difficulty communicating are common signs of dementia and depression.

Laboratory Tests

A complete blood count (CBC) can assess your RBC concentration, which can be normal or low in vitamin B12 deficiency. 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.

Vitamin B12 deficiency can be confirmed by a blood measurement of the vitamin level. This is not a standard screening test, but it is a simple blood test that you can have if your medical team is concerned that you may have a vitamin B12 deficiency.

Imaging Tests and Specialized Tests

Other tests, such as imaging tests and nerve conduction studies (NCV) can be helpful in assessing the effects of vitamin B12 deficiency, but they do not produce a specific pattern of results that corresponds with this deficiency.


Vitamin B12 deficiency can be managed with dietary intake, or by oral (by mouth) or intramuscular (IM) injections of the vitamin.

Foods that are rich in vitamin B12 include meat, chicken, fish, dairy products, and fortified cereals and grains. If decreased absorption is among the causes of your vitamin B12 deficiency, then you may need to have an injection so that it will be absorbed directly into your body, rather than relying on your diet and GI system.

Recovery from 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 6 to 12 months.

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.


It is possible that you may continue to suffer from lasting deficits, 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.

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, instead, going through periods of gradual or intermittent declines in your vitamin B12 level—which results 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 preventative treatment such as regularly scheduled vitamin B12 injections to avoid becoming deficient in this vitamin.

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