A person with Crohn’s disease will experience abdominal pain and unintentional weight loss. They may also have difficulty absorbing certain foods, resulting in nutrient deficiencies. One that commonly occurs is a vitamin B12 deficiency.

A person holding their stomach with an empty plate of food beside themShare on Pinterest
Charles Gullung/boonchai wedmakawand/Getty Images

Crohn’s disease, a form of inflammatory bowel disease (IBD), is a lifelong condition that results in inflammation and irritation of the digestive tract. Crohn’s disease commonly affects the small intestine and the beginning portion of the large intestine. This section of the intestine is responsible for absorbing nutrients such as vitamin B12.

Vitamin B12 is naturally present in certain foods and is also available as a dietary supplement. It plays an important role in various bodily functions, including developing the central nervous system, red blood cell formation, and DNA synthesis.

This article explains why a person with Crohn’s disease may have a vitamin B12 deficiency and how a doctor may diagnose it. It also looks at recognizing, preventing, and reversing a vitamin B12 deficiency.

Vitamin B12 deficiency is common among people with Crohn’s disease. The disease typically affects the ileum, the last portion of the small intestine, which is where the absorption of vitamin B12 occurs.

Some people with Crohn’s disease may undergo surgical removal of part or all of the ileum, and this can also lead to difficulty absorbing vitamin B12.

Warning signs of deficiency

A person with vitamin B-12 deficiency may present with symptoms such as:

A person with vitamin B12 deficiency may also experience various neurological symptoms, including:

A person should consult a doctor if they experience any of the above symptoms. The doctor can rule out other possible causes of the symptoms.

The doctor will usually begin the diagnostic process by asking about the person’s symptoms and medical history and then carrying out a physical exam.

They might also conduct a neurological exam if the person is experiencing difficulty concentrating or has any tingling or numbness in their hands or feet.

Blood tests

Healthcare professionals will order laboratory tests to confirm a diagnosis.

Initial blood tests may include a complete blood count (CBC) to measure vitamin B-12 and folate levels in the blood.

A vitamin B12 level of fewer than 200 picograms per milliliter indicates deficiency. A CBC test will likely show a decrease in hemoglobin and hematocrit in a person with a vitamin B12 deficiency.

If a person’s vitamin B12 level remains unclear, a doctor may order additional tests, such as a methylmalonic acid (MMA) blood test. This test measures the blood level of MMA, which the body produces during metabolism. Vitamin B12 has a role in metabolism. Therefore, if the body is deficient in vitamin B12, the level of MMA is likely to increase.

Another type of test is the homocysteine test to measure the level of an amino acid called homocysteine in the blood. Vitamin B12 breaks down homocysteine to produce components that the body uses. A vitamin B12 deficiency will likely result in a higher level of homocysteine in the blood.

A person can take steps to prevent or even reverse a vitamin B12 deficiency.


According to the Office of Dietary Supplements, the recommended daily allowance of vitamin B12 for a person over 18 years is 2.4 micrograms (mcg).

Vitamin B12 is available in supplements in different doses. These supplements contain either vitamin B12 alone or a combination of B-complex vitamins.

Supplements that contain only vitamin B12 tend to contain doses in the range of 500–1,000 mcg, whereas supplements that contain multiple B-complex vitamins provide 50–500 mcg of vitamin B12.

These supplements do not normally require a prescription, and people can buy them over the counter in supermarkets or pharmacies. Vitamin B12 is also available in tablets and lozenges that people place under the tongue.


A person with a severe vitamin B12 deficiency or difficulty absorbing vitamin B12 may require an injection of vitamin B12. Some people refer to this as a B12 shot. The injection, which doctors deliver into the muscle, typically contains vitamin B12 in the form of cyanocobalamin or hydroxocobalamin.

In a 2019 study, participants with Crohn’s disease reported improvements in their symptoms shortly after receiving a vitamin B12 injection.

How to include vitamin B12 in the diet

A person can also increase their vitamin B12 intake by following a diet rich in vitamin B12. Foods that are high in vitamin B12 include:

Learn more about foods that can increase and reduce vitamin B12 levels.

Other possible causes of a vitamin B12 deficiency include:

A person with Crohn’s disease may also benefit from other nutritional supplements. These may help ensure that a person gets the correct amount of vitamins and nutrients, especially if they are not absorbing enough from food alone.

Some supplements that a person may benefit from include:

Crohn’s disease is a chronic condition that results in digestive tract inflammation. A person with Crohn’s disease may have trouble absorbing certain vitamins, such as vitamin B12, if they have undergone the removal of part or all of the ileum or if the disease affects their ileum.

Other causes of a vitamin B12 deficiency include certain medications, a vegan or vegetarian diet, and certain infections.

A doctor will usually diagnose a person with a vitamin B12 deficiency based on a physical examination and blood tests. They may advise the person to take supplements, receive vitamin B12 injections, or eat more foods rich in vitamin B12, such as seafood, vegetables, and meat.