How Vitamin B12 Deficiency Affects the Body

Vitamin B12 Deficiency Symptoms

Vitamin B12 deficiency is one of the most prevalent nutritional deficiencies. It causes a range of symptoms, such as fatigue, forgetfulness, and 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.

B12 Function

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, then it causes inflammation and toxic damage to the body.

Symptoms and Effects

Anemia is a diminished function of the red blood cells (RBCs). The chief clinical manifestation of B12 deficiency is megaloblastic anemia, which is a type of anemia that often produces fatigue and tachycardia (rapid heart rate), and sometimes dizziness.

Vitamin B12 is a nutrient required for normal red blood cell production.

RBCs deliver energy-producing oxygen throughout the body to power all of the body’s needs. Megaloblastic anemia can be diagnosed by a blood test.

Peripheral neuropathy is a type of nerve impairment. This means that nerves themselves may be damaged or that there is a deficiency of myelin. Myelin 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.

Signs of B12 Deficiency

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 usually affect the feet and hands and may extend to include the arms and legs as well. The most common symptoms include:

  • Numbness
  • Tingling
  • 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:

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

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 may increase the risk of stroke among young people who are not otherwise at risk of stroke. Whether or not there is a link is highly controversial, and the risk may result from excess homocysteine levels.

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:

  • Balance problems
  • Numbness, tingling
  • Spasticity
  • Weakness

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

Associated Conditions

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.


Below are some common 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 non-vegan 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 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 may not be adequately absorbed into the body, and instead, it is eliminated through bowel movements.

Excessive Alcohol Use

Heavy alcohol use causes changes in the lining of the stomach, interfering with production of intrinsic factor, causing B12 deficiency. Intestinal disease such as Crohn’s disease and celiac disease can prevent the proper absorption of vitamin B12 in the small intestines, causing a deficiency even if there is enough vitamin B12 in the diet.

Autoimmune Disease

Pernicious anemia is an autoimmune disease that reduces or eliminates intrinsic factor, the protein in the stomach that binds dietary B12 so that it can be absorbed. This leads to B12 deficiency through malabsorption. This type of B12 deficiency cannot be treated with oral B12 replacement and requires treatment with vitamin B12 shots.

Symptoms of pernicious anemia include:

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

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

  • Chloramphenicol: an antibiotic used to treat infections
  • Colchicine: a medication used to treat gout
  • Many medications used for the treatment of heartburn
  • Metformin: a medication used to treat diabetes

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.



“I am convinced that many evangelicals are not truly and soundly
converted. Among the evangelicals, it is entirely possible to come
into membership, to ooze in by osmosis, to leak through the cells
of the church and never know what it means to be born of the
Spirit and washed in the blood.”
– A W Tozer.

“We must frankly face the fact that there is in this teaching a
a revolutionary element which could be dangerously subversive of
our existing ways of thought.”
– Lesslie Newbigin

“Let me learn by paradox
that the way down is the way up,
that to be low is to be high,
that the broken heart is the healed heart,
that the contrite spirit is the rejoicing spirit,
that the repenting soul is the victorious soul,
that to have nothing is to possess all,
that to bear the cross is to wear the crown,
that to give is to receive,
that the valley is the place of vision.”
-Collection of Puritan Prayers and Devotions.

“When we become too glib in prayer we are most surely talking to
ourselves.” – A. W. Tozer

“When filled with holy truth the mind rests.”- C.H. Spurgeon

“When the Lord reveals His will to us and we obey, our mission
will be a success regardless of the results.”
– Chinese house church leaders

“Those who are God’s true witnesses are firmly anchored in Him,
in love or in suffering, no matter what God may give or take away.
They do not set much store by their own methods; if they prove
helpful to their spiritual life, well and good. But God, in his loving
foresight, often shatters their foundations and thus they frequently
find themselves thwarted.”
– Johannes Tauler.

“Worship renews the spirit as sleep renews the body.”
– Richard Clarke Cabot

“It is simply absurd to say you believe or even want to believe, in
Him, if you do not do anything He tells you.” – George Macdonald

“The saintly Andrew Bonar used to soak his pillow with tears every
Saturday night in Scotland as people below trampled the streets
returning from the taverns and shows. He would cry from the
depths of his agonizing heart, “Oh! They perish, they perish!”