How Vitamin B12 Deficiency Affects the Body

Fatigued woman with vitamin B12 deficiency

Vitamin B12 deficiency is one of the most prevalent nutritional deficiencies. It causes an array of symptoms ranging from fatigue to forgetfulness to tingling of the hands and feet. The reason for the wide variety of symptoms is that vitamin B12 plays a principal role in numerous body functions.

What Does Vitamin B12 Do?

Vitamin B12 has an important function in the production of DNA, which is the body's genetic code.

DNA directs proper formation of every part of the body.

Vitamin B12 also reduces homocysteine, one of the body’s naturally occurring chemicals. If homocysteine is not properly metabolized because of a vitamin B12 deficiency, then it causes inflammation and toxic damage to the body. This is why the effects of vitamin B12 deficiency have an impact on so many body systems.

Symptoms and Effects of Vitamin B12 Deficiency 

Pernicious anemia is a type of anemia characterized by large, dysfunctional red blood cells (RBCs). Megaloblastic anemia is another description of this type anemia, which develops when the body does not have enough vitamin B12, a nutrient required for normal red blood cell production. RBCs deliver energy-producing oxygen throughout body to power all of the body’s needs.

Symptoms of pernicious anemia include:

  • Fatigue
  • Lack of energy
  • Lightheadedness
  • Depression 
  • Headaches
  • Rapid heart beat 
  • Ringing in the ears

Peripheral neuropathy is a type of nerve damage. This means that nerves are actually damaged or that there is a deficiency of myelin, which is a protective covering of the peripheral nerves. Vitamin B12 is a co-factor in myelin formation, and thus a vitamin B12 deficiency prevents myelin from forming as needed.

With B12 deficiency, direct nerve damage combined with a decrease of myelin interferes with normal nerve function. The peripheral nerves control movement and sensation of the body.

Symptoms of peripheral neuropathy include:

  • Tingling
  • Numbness
  • Weakness 

Dementia is a disease characterized by memory loss and behavioral changes. There are many causes of dementia, and vitamin B12 deficiency is one of the more recently recognized causes. Scientific research suggests that the dementia associated with vitamin B12 deficiency may be a result of elevated homocysteine levels.

Symptoms of dementia include:

  • Forgetfulness 
  • Absentmindedness
  • Problem solving difficulties
  • Inability to concentrate
  • Loss of ability to take care of oneself
  • Apathy 
  • Hallucinations  

Depression is a possible manifestation of vitamin B12 deficiency, and may be accompanied by anemia or dementia.

Stroke is a medical condition characterized by interruption of blood flow to the brain, causing a physical or mental handicap. Vitamin B12 deficiency is one of the known causes of stroke among young people who are not otherwise at risk of stroke. This has been found to result from excess homocysteine levels.

Less Common Symptoms of Vitamin B12 Deficiency

Myelopathy means disease of the spinal cord.

Vitamin B12 deficiency causes a type of spine disease called subacute combined degeneration of the spinal cord, which is loss of the protective myelin of certain areas of the spinal cord that control moment, balance and sensation. 

Symptoms of subacute combined degeneration of the spinal cord include:

  • Weakness 
  • Numbness, tingling 
  • Spasticity 
  • Balance problems 

Heart failure has also been associated with vitamin B12 deficiency. Specifically, enlargement of the heart and diminished heart function heart have been linked to elevated homocysteine levels.

Symptoms of heart failure include:

  • Fatigue
  • Shortness of breath 
  • Intolerance of exercise
  • Dizziness
  • Leg swelling

Tongue swelling also result from vitamin B12 deficiency. Glossitis is the name used to describe a painful, unusually smooth tongue that can result from this nutritional deficiency.

Thyroid disease and Multiple Sclerosis (MS) are both conditions believed to be related to an autoimmune process. An autoimmune disease is a condition caused by the body attacking itself.

Intrinsic factor deficiency is an autoimmune disease that results from a ‘self’ attack on the region of the stomach that is involved in vitamin B12 absorption. Often, individuals who have thyroid disease or MS also have intrinsic factor deficiency and its associated vitamin B12 deficiency.

Causes of Vitamin B12 Deficiency

Low Dietary Intake

The most common cause of vitamin B12 deficiency is a lack of vitamin B12 in the diet. Vitamin B12 is a nutrient that is only found in animal products such as meat, chicken, fish, eggs and dairy. Therefore vegans are at especially high risk of low nutritional vitamin B12, as are individuals who do not eat enough of these vitamin B12 rich foods.

Some foods are fortified with vitamin B12, and if you want to get your vitamin B12 through vegan foods, you have to make an effort to seek out those types of foods.

Low Absorption 

Vitamin B12 is absorbed by the small intestine, but it requires some preliminary processing in the stomach first. Therefore, some conditions that affect the stomach or the small intestine can interfere with proper vitamin B12 absorption. Intrinsic factor is a protein produced in the stomach that combines with vitamin B12 before it can be absorbed in in the small intestine.

Autoimmune disease, gastric bypass surgery and inflammation of the stomach are all situations that interfere with the production and function of intrinsic factor, and thus the vitamin B12 in the diet is not absorbed into the body, and it is eliminated through bowel movements.

Heavy alcohol use causes changes in the lining of the stomach and thus interferes with production of intrinsic factor, causing B12 deficiency.

Intestinal disease such as Crohn’s disease and Celiac Disease can interfere with proper absorption of vitamin B12 in the small intestines, causing a deficiency even if there is enough vitamin B12 in the diet.

Medications can interfere with vitamin B12 absorption. The most common medications that can cause low vitamin B12 levels include:

Metformin: a medication used to treat diabetes

Colchicine: a medication used to treat gout

Chloramphenicol: an antibiotic used to treat infections

Many medications used for the treatment of heartburn

A Word From Verywell

If you have vitamin B12 deficiency, many of the effects can be reversed, particularly at the early stages. In general, if your vitamin B12 deficiency is caused by a nutritional deficiency, supplements or fortified foods can help improve your vitamin B12 levels.

If impaired absorption is the reason for your vitamin B12 deficiency, it is generally considered more effective to get your vitamin B12 supplementation through injections rather than by mouth, as this allows the nutrient to enter into the body’s tissue directly.


Desouza C, Keebler M, McNamara DB, Fonseca V, Drugs. Drugs affecting homocysteine metabolism: impact on cardiovascular risk. 2002;62(4):605-16.

Cerit L, Duygu H, Gulsen K, Kemal H, Tosun O, Ozcem B, Cerit Z, Gunsel A, Kardiol Pol. The relation between vitamin B12 and SYNTAX score. 2017;75(1):65-70.

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