Crohn’s Disease and Anemia: What’s the Link?

Medically Reviewed by Minesh Khatri, MD on May 28, 2024
4 min read

If you have Crohn’s disease, you might feel tired or lethargic most of the time. While these are symptoms of Crohn’s, they might mean you also have anemia. It’s a common problem, with just under half of people (42%) with Crohn’s developing anemia within a year of their diagnosis.

Most symptoms of anemia, like feeling tired, happen because there’s not enough blood getting to your cells and tissues, a condition doctors call hypoxia. This can take a toll on your overall quality of life.

Many things can cause anemia. The most common cause of anemia is low levels of iron, known as iron-deficiency anemia (IDA). This is the most common type in people with Crohn’s. The long-term irritation and swelling in your gut that often happens with Crohn’s can mess up your body’s ability to absorb and use iron properly.

But the most common cause of iron deficiency in those with Crohn’s is linked to slow blood loss from things like bleeding in the digestive tract. The bleeding usually begins when Crohn’s-related sores called ulcers start to spread inside your colon. Your gut is made up of several blood vessels. When you have a flare-up, the sores cause tiny tears in your gut’s lining. They can cause your blood vessels to burst and bleed.

You might be unaware that you’ve been losing blood for a long period of time because you might not have other symptoms. If you have IDA, this may cause it to go untreated. 

Studies also show IDA is more common in children and teens who have Crohn’s and other forms of IBD than it is in grownups. It happens in over 80% of childhood IBD cases, compared to 55% of adult cases.

Vitamin B12 and folic acid deficiencies, which can be caused by Crohn’s, can also lead to anemia.

Symptoms of IDA can include:

  • Anemia from chronic inflammation
  • Fatigue
  • Dizziness
  • Headaches
  • Cold hands or feet
  • Pica
  • Ice craving
  • Pale skin
  • Shortness of breath
  • Fast-beating or pounding heart, called palpitations
  • A type of chest pain called angina
  • Abnormal muscle or nerve spasms in your gut, called motility disorder
  • Nausea
  • Weight loss
  • Belly pain

If the lack of oxygen in your blood affects your brain, it can cause issues like headache, vertigo, lethargy, and problems with thinking or remembering.

If you have Crohn’s and you’ve noticed bleeding in your stool, or you suspect anemia, it’s best to talk to your doctor right away and get checked out for IDA. To diagnose it, your doctor will do a full physical exam, take a detailed medical history, and ask you questions about the symptoms you have.

They’ll also run a blood test called complete blood count.

The test checks your:

  • Red blood cell size. These cells are the ones that carry oxygen to your organs and tissues.
  • White blood cells. It measures the number of these cells you have to fight infection.
  • Hematocrit. It checks for the percentage of red blood cells by volume in your blood. For adult women, the normal levels are generally between 35.5% and 44.9%. For adult men, the levels are between 38.3% to 48.6%. These values may change depending on your age.
  • Hemoglobin. It measures this protein in your red blood cells that carry oxygen. Low levels of it are a sign of anemia. The normal levels for an adult woman are 11.6 to 15 g/dL and 13.2 to 16.6 g/dL for men.

A separate test checks how much iron your body has. It also measures your ferritin, the protein responsible for storing iron in your body. Low levels of ferritin are a sign of low iron levels.

Your doctor also might do a test to look at the size and shape of your red blood cells or get a sample of your bone marrow, before they diagnose you with anemia.

When you have Crohn’s, it’s important to check for IDA:

  • At the time of your Crohn’s diagnosis
  • Every 3 months when your Crohn’s flare-up is active
  • Every 6-12 months when you’re in remission

To treat IDA, doctors recommend taking iron supplements. There are many ways to boost your iron intake. These include:

Oral iron supplements. These are available in pills that you take by mouth. Your doctor will likely recommend these if your hemoglobin levels are below 10 g/dL and you’re in remission. You can buy these over the counter. For adults, the recommended dose is about 100 milligrams per day. For kids, it’s calculated by body weight. It’s 2-3 milligrams per kilogram (2.2 pounds). These are available as liquids for infants and children.

Intravenous (IV) iron therapy. This is also known as parenteral iron supplementation. It’s taken through an injection in your vein. It’s recommended if your Crohn’s disease is active or if you’re unable to tolerate oral iron supplements.

If your IDA is severe, you may need a blood transfusion at a doctor’s office or hospital to raise your hemoglobin levels.

Things to Keep in Mind When Taking Oral Iron Supplements

To help your body absorb iron when you’re taking oral supplements, you should:

  • Take them on an empty stomach. But if they make you nauseous, you can take them with food.
  • Don’t take them with antacids. This can disrupt absorption. Wait 2 hours before or 4 hours after you take your antacids to take your iron supplements.
  • Take them with vitamin C. This can include orange juice or a vitamin C supplement.

Iron supplements can cause side effects, such as:

  • Constipation
  • Black stools
  • Nausea

If you’re unable to tolerate them, let your doctor know.

You may need to take supplements for several months or a year before your tests show higher iron levels. But the good news is you may feel better soon after starting them, sometimes within a week.

Your doctor may reorder blood tests during your treatment to monitor your iron levels and make sure you’re heading in the right direction.