Vitamin B12 Deficiency: Symptoms, Causes & Treatment

Updated in March 2024

A vitamin B12 deficiency can cause symptoms such as fatigue, shortness of breath, tingling in the hands and pale skin. In children, a B12 deficiency can lead to growth delays and affect development.

Vitamin B12, also known as cobalamin, is important for the development and maintenance of normal central nervous system functioning. It also plays a role in maintaining heart health and producing blood cells. 

You notice symptoms of a possible vitamin B12 deficiency, you should see a doctor or registered dietitian for assessment and possible treatment. Treatment may involve B12 injections, oral supplements and increasing B12 foods in your diet.

Imagem ilustrativa número 2

Main symptoms 

Low vitamin B12 levels can lead to the following symptoms:

  • Loss of sensitivity or tingling in the hands, legs or feet;
  • Frequent fatigue and weakness;
  • Palpitations;
  • Shortness of breath;
  • Sores in the mouth and tongue;
  • Memory loss and mental confusion;
  • Loss of appetite;
  • Eye twitching

In children, vitamin B12 deficiency can cause delays in growth and general development. Furthermore, a lack of this vitamin can also cause vision changes, irritability and megaloblastic anemia, a type of anemia where the bone marrow produces red blood cells that are larger than normal.

Common causes

A vitamin B12 deficiency can occur for many reasons, such as:

  • Changes in the stomach: Pernicious anemia can be caused by a decrease in intrinsic factor levels. This is a protein that is necessary for the absorption of B12 in the stomach. In addition, gastric acid is helps to separate B12 from the food that contains it. Gastritis or the use of certain medications can block or neutralize the acidity of stomach acid, which can interfere with the concentration of this vitamin in the stomach.
  • Changes in the intestine: People with Chrons disease who have a compromised ileum or have had their ileum surgically removed are unable to absorb B12 efficiently. Another common intestinal condition that can lead to B12 deficiency is the overgrowth of bacteria or parasites.   
  • Changes to diet: Animal-based foods are a natural source of B12. Therefore, people who have little-to-no intake of food like meat, fish, eggs, cheese and milk may experience a deficiency. People at highest risk for a deficiency are older adults, alcoholics, strict vegetarians or people with eating disorders. 

In addition, the use of medications, like antibiotics, metformin and medications that treat gastritis or ulcers (like omeprazole) may experience decreased B12 absorption in the intestine. Therefore, many people who use these medications may also be advised to supplement. 

Treatment options

Treatment for a vitamin B12 deficiency varies depending on the underlying cause. It can involve the use of injections or supplements, in addition to adding more B12 foods to your diet. 

1. Vitamin B12 injections

Vitamin B12 can be administered as intramuscular injections in the form of hydroxocobalamin. These injections are typically indicated for cases of B12 deficiencies caused by pernicious anemia, bariatric surgery or specific diets (like a vegetarian diet).

The generally recommended dosage of intramuscular vitamin B12 is 1000 mcg, once a week, for four weeks, until B12 levels in the blood are back to normal. After this period, the doctor may prescribe 1000 mcg of intramuscular vitamin B12, once a month. Learn more about B12 injections.

2. Supplements

B12 deficiencies caused by low intake of this vitamin in the diet may be treated with oral vitamin B12 supplements.

The doctor may prescribe B12 supplements for people with polycythemia, (which is an increase in the number of red blood cells in the blood), an allergy to cobalt or cobalamin, or for those who are in the post-operative period.

3. Food

Increasing intake of foods rich or fortified with vitamin B12 is mainly recommended for people who generally do not eat B12 foods.

Some foods that are fortified with this vitamin and/or naturally contain vitamin B12, such as beef, fish, eggs and milk. 

Also recommended: Top 16 Vitamin B12 Foods (& Recommended Daily Dose)