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What Causes Vitamin B12 Deficiency?

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Vitamin B12, or cobalamin, is a type of B vitamin. The body stores this water-soluble vitamin in the liver. Vitamin B12 is essential for several critical processes in the body, including producing red blood cells, DNA synthesis, and keeping the heart and nervous system healthy. Vitamin B12 is also essential during pregnancy for the normal development of a baby's brain and nervous system.

A B12 deficiency can cause various medical problems, including vitamin deficiency anemia, nerve damage, balance problems, and mental issues like poor memory, confusion, depression, and dementia.

Please continue reading to learn more about vitamin B12 deficiency, including what causes it and how it is diagnosed and treated.

What is vitamin B12 deficiency anemia?

Red blood cells carry oxygen to every organ in the body. The body needs vitamin B12 to make enough red blood cells that are healthy. When there is a B12 deficiency, there aren't enough healthy red blood cells. This condition is called anemia, or more specifically, pernicious anemia. As a result of pernicious anemia, the cells, tissues, and organs in the body don't get oxygen and cannot work properly. Many of the symptoms of vitamin B12 deficiency occur due to the cells in different parts of the body not getting enough oxygen.

Anemia caused by vitamin B12 deficiency is a type of megaloblastic anemia. In this type of anemia, the red blood cells are abnormally large and oval-shaped rather than round. As a result, the bone marrow doesn't make enough red blood cells. Also, red blood cells tend to die more quickly than expected.

What is the main cause of vitamin B12 deficiency?

The most common cause of vitamin B12 deficiency is the lack of a substance called intrinsic factor—this is a glycoprotein secreted by the stomach. Intrinsic factor enables the body to absorb vitamin B12. Without this substance, the body cannot absorb vitamin B 12 present in food.

A lack of intrinsic factor occurs when the immune system mistakenly attacks the cells in the stomach that produce this substance. People with related autoimmune conditions, such as thyroid disease and type 1 diabetes, are at higher risk of developing anemia due to vitamin B12 deficiency.

Another potential cause of vitamin B12 deficiency is not enough B12 in the diet. Vitamin B12 is mainly found in meat, poultry, eggs, shellfish, and dairy products. Therefore, people who eat a strict vegetarian diet (no animal proteins including milk and eggs) are at risk of developing low B12 levels. Also, people who use certain medications, such as proton pump inhibitors (PPIs), for a long time can suffer from low B12 levels due to poor absorption and bacterial overgrowth in the small intestine.

Other causes of vitamin B12 deficiency include the inability to absorb and get enough vitamin B12 after surgery on the stomach, which can be the case with bariatric patients (people with a body mass index (BMI) that is equal to or greater than 30). It can also occur in people with intestinal diseases such as celiac disease or Crohn's disease. Vitamin B 12 deficiency may develop due to abnormal bacterial growth in the small intestine. Sometimes, if a person ingests a tapeworm in contaminated fish, the tapeworm can sap nutrients, including vitamin B12 and folic acid, leading to a vitamin deficiency anemia.

How do you become B12 deficient?

As mentioned, the most common cause of vitamin B 12 deficiency is the lack of intrinsic factor. This can occur due to a genetic predisposition (vitamin B12 deficiency anemia is more prevalent in people with a northern European heritage or with a family history of this condition). Vitamin B 12 deficiency can also be linked to an autoimmune disorder such as thyroid disease or type 1 diabetes. Medical conditions such as chronic gastritis (inflammation of the stomach) or gastrectomy (partial or total surgical removal of the stomach) can leave the body without enough intrinsic factor. 

What happens when your vitamin B12 is low? 

Without enough vitamin B12, the body cannot make red blood cells. As a result, the tissues and organs don't get enough oxygen, which can cause a wide range of symptoms.

In people with vitamin B12 deficiency, symptoms may include fatigue, lack of energy, dizziness, shortness of breath, irregular or fast heartbeat, pale or yellowish skin, numbness or tingling in the hands and feet, smooth or tender tongue, decreased appetite, weight loss, diarrhea, muscle weakness, unsteadiness, trouble walking, mental confusion, forgetfulness, irritability, and personality changes.

It is worth remembering that each person's symptoms of vitamin B12 deficiency can be different. Also, vitamin B12 deficiency develops gradually over months to years. The signs and symptoms of vitamin deficiency anemia may be subtle at first and slowly worsen as the levels of vitamin B12 fall. Also, the symptoms of megaloblastic anemia due to folic acid and/or vitamin B 12 deficiency can mimic many other health problems. Do not self-treat with OTC vitamin supplements. Ask your doctor to evaluate you if you suspect B vitamin deficiencies.

How do doctors diagnose and treat vitamin B 12 deficiency?

Doctors can diagnose vitamin deficiency anemia by obtaining a medical history, performing a physical examination, and ordering blood tests. For example, a blood test for vitamin B12 deficiency may check whether you have enough hemoglobin. Another blood test may check whether your red blood cells are larger than normal. Occasionally, a bone marrow biopsy may be required to rule out other medical conditions or assess iron stores in the body.

The treatment for vitamin B12 deficiency depends on the patient's age, health status, cause of vitamin B12 deficiency, and personal preferences. Vitamin B12 and folate deficiency are usually treated together because they are difficult to tell apart and often occur simultaneously.

If you are diagnosed with vitamin deficiency anemia, your doctor may advise you to include more foods rich in folic acid and vitamin B12, such as meat, eggs, poultry, dairy products, and fortified cereals.

Treatment may consist of vitamins in the form of supplements, including folic acid pills and vitamin B12 shots. Vitamin B12 replacement is often given by intramuscular injection because absorption through the stomach and small intestine may be inadequate. However, if vitamin B12 shots are not convenient, you can take a daily vitamin B12 supplement by mouth.

You may need to take vitamin supplements long-term or for the rest of your life. Vitamin B12 is available both by prescription and over-the-counter. However, it is important to seek medical advice and proper diagnosis of vitamin B12 deficiency and its cause before using vitamin supplements.