Anemia due to too low vitamin B12


Vitamin B12 is needed for the body to form red blood cells. If you have too little B12 you may have anemia. B12 is not produced in the body but you get it through the food. B12 is found in food from the animal kingdom, mainly in meat and dairy products.

In this text you can read about the most common symptoms of anemia due to too little B12. You can also read more about when to seek care and different treatments. Anemia can also be because you have too little iron. You may also have anemia for other reasons.

Symptoms of anemia due to too little vitamin B12

The purpose of the red blood cells is to transport oxygen from the breathing air to all parts of the body. Oxygen is needed for most of the body’s functions, such as blood formation, metabolism, and energy production. This means that a lack of red blood cells can cause many different types of symptoms.  

Common symptoms of anemia are you

  • feeling tired and powerless
  • have trouble concentrating
  • feel dizzy
  • feel that you are breathing easier than before
  • gets palpitations
  • gets a headache
  • gets earache.

Anemia due to too little B12 can also cause mucous membranes. For example, there may be cracks in the mouth pipes or tongue sweat. Tungsveda means that the knotty surface of the tongue disappears and instead it becomes smooth, red, glossy and scorching.

Deficiency of B12 can also appear as a nuisance from the nervous system. It can be in the form of knitting, numbness and impaired feeling, starting with the feet. You may feel insecure as you walk and get impaired reflexes in the calves and soles. Severe B12 deficiency can also cause symptoms such as impaired memory, depression and impaired vision.

It is common for the symptoms of anemia due to too little B12 to increase slowly over several months and sometimes over several years.

When should I seek care?

Seek care at a health care center if you suspect you have anemia. There you can get a referral to a doctor who specializes in, for example, blood disorders. 


At the health center, the doctor does a general body examination. You may also submit a blood test to check how much hemoglobin you have in your blood. It is often shortened to Hb. Sometimes it is also called blood value. The test shows if you have anemia and what type of anemia you have. 

If the doctor suspects you have B12 deficiency ask them if the mucous membranes in the mouth are burning and red, if you have decreased sensation in the feet and if you have impaired reflexes.

Additional blood tests

The result of the first blood test shows what direction the investigation should have. If the red blood cells are enlarged, you may be deficient in B12 or folic acid. Then the content of these substances is measured in the blood. Folic acid deficiency can cause similar symptoms to vitamin B12 deficiency, and you may have these deficiencies simultaneously. There are also blood tests that can show if you have pernicious anemia, which causes B12 deficiency.


Sometimes an investigation is also done with gastroscopy. A gastroscope consists of a flexible tube that is passed down to the stomach through the mouth. The gastroscope transmits images of the stomach and upper part of the small intestine to a monitor. Using the gastroscope, the doctor can also take samples from the lining of the stomach to examine it in a microscope.

Bone marrow Examination

You may also be able to do a bone marrow examination, which depends on what the blood tests showed. Then you are anesthetized first in the skin and then deeper down to the retina at the place where the test is to be taken, usually on the back of the hip. Then the doctor inserted a needle to suck out the bone marrow, which is then examined under a microscope. The survey takes fifteen to thirty minutes.

Treatment for anemia due to too little vitamin B12

If you have anemia due to too little B12, you need vitamin B12 treatment.

Tablets or injections

If you have been diagnosed with pernicious anemia, you will be treated with B12 for life. You may be given tablets that you should take every day or injections every three months. The doctor will discuss with you which one you prefer.

You always get injections initially if you have very low blood levels or if you have symptoms from the nerves in the legs.

Unusual with side effects

It is very uncommon to get side effects from the treatment.

Blood levels will quickly improve if you receive treatment

Blood levels tend to rise rapidly with treatment and become normal after a few weeks if you have moderate anemia. It can take a couple of months if you have severe anemia with very low anemia. If you have symptoms from the nervous system, it often takes longer to get rid of them. If severe nervous system symptoms have occurred, these may persist.

It is unusual to need blood transfusions

Because B12 deficiency usually causes the blood level to decrease slowly, the body has to adapt. This means that it is very uncommon to need blood transfusion treatment, although the blood value is very low. Blood transfusion is more common in cases of anemia that occurs rapidly.

Anemia may be due to something else

If your blood value does not get better by B12 treatment, it may be because there is another cause of the anemia.

What happens in the body?

The body needs B12 to form red blood cells. In the red blood cells, there is hemoglobin. It is a ferrous substance that captures and transports oxygen from the lungs to the body’s cells. In a person with B12 deficiency fewer red blood cells are formed than in a person without deficiency.

B12 is also needed for, for example, the nervous system and metabolism to function.

You get B12 through the food

Vitamin B12 cannot be made in the body but you get it through the food you eat. When B12 enters the duodenum, it must bind to a protein called intrinsic factor, IF, in order to be absorbed into the body.

B12 is found in food from the animal kingdom

Vitamin B12 is mainly found in meat and dairy products. The largest quantities are found in meat, liver, fish, seafood, eggs, milk and cheese.

You who only eat vegan diet may have difficulty getting enough B12 through the food. Some vegetable drinks such as soy, oat or rice beverages are enriched with B12. It may be good to choose one of these if you do not eat meat or dairy products.

Be careful not to give rice drinks to children younger than six years, as rice may contain arsenic.

How much B12 do I need?

You who usually eat animal food get in you between 5 to 15 micrograms of B12 vitamin a day. Adults should receive at least 2 micrograms of vitamin B12 a day. Excess vitamin B12 is stored in the liver and the layers last for several years.

Different causes of anemia due to too little B12

B12 deficiency can occur in several ways.

Pernicious anemia

Pernicious anemia is the most common cause of B12 deficiency and is caused by a deficiency of the protein IF, the intrinsic factor, which is formed in the stomach and is needed for B12 to be absorbed into the body.

The most common cause of lack of IF is a special form of inflammation in the lining of the stomach that you may have had for a long time. The inflammation is called chronic autoimmune gastritis. Then the own immune system attacks the cells that produce IF and hydrochloric acid in the stomach. It is a so-called autoimmune reaction. The reaction can last for a long time, sometimes for several years.

Other autoimmune diseases increase the risk of chronic autoimmune gastritis

People who have other so-called autoimmune diseases, such as type 1 diabetes, autoimmune thyroid inflammation, and Addison’s disease, more often have this special form of inflammation of the gastric mucosa. Thus, they also have an increased risk of having pernicious anemia.

Chronic autoimmune gastritis has no association with gastric ulcers.

How common are pernicious anemia and B12 deficiency?

About 1% of the population has pernicious anemia. The disease is more common at older ages. It is uncommon to have pernicious anemia before the age of 30.

Pernicious anemia can be hereditary

You who have close relatives with chronic autoimmune gastritis are more likely to have the inflammation yourself and thus pernicious anemia.

There is also a very unusual, hereditary form of anemia due to too little vitamin B12. The disease means that you have a deficiency of the protein IF without having chronic gastritis.

Disorders of the bacterial flora

Another cause of B12 deficiency may be prolonged treatment with certain drugs that may interfere with the gut flora of the intestine so that the absorption of B12 becomes worse. This applies to some medicines for heartburn, ulcers, diabetes, and systemic sclerosis.

Diseases of the intestine

Another cause of anemia due to too little B12 may be that you have a bowel disease that impairs B12 uptake. Some examples are gluten intolerance and inflammatory bowel diseases such as Crohn’s disease. It is common to also have a deficiency of iron and folic acid if you have a deficiency of B12 due to bowel disease.

Stomach surgery

If part of the stomach is disconnected, as in some obesity operations, the cells that produce the protein IF may become too few. Then B12 deficiency can occur.

It may also happen if part of the stomach is removed for example due to ulcers. This is very unusual since gastric ulcer is now treated with drugs.

Can I prevent anemia due to B12?

You who have gluten intolerance or have been operated on in the stomach may need preventive treatment with B12, iron and folic acid. Discuss with your doctor if this may be appropriate for you.

Pernicious anemia cannot be prevented.

You who only eat vegan food may need supplements because vitamin B12 is only found in foods from the animal kingdom.

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