This type of anemia occurs when you’re not getting enough iron or are losing too much iron. Your body needs adequate iron to produce hemoglobin, a substance in red blood cells that enables them to carry oxygen. This is why iron-deficiency anemia may cause fatigue and leave you feeling short of breath.
Although low iron levels in your body can have a number of potential causes, in people with Crohn’s disease, the most common cause is blood loss in the digestive tract. When this happens, people “are usually unaware that they are losing blood,” says James F. Marion, MD, a gastroenterologist and IBD expert at Mount Sinai Hospital in New York City. That’s because the blood loss can happen gradually over a long period of time without overt symptoms.
In people with Crohn’s disease, Dr. Marion says, this blood loss usually occurs because of disease activity. The digestive tract contains lots of blood vessels, he notes, which can rupture when Crohn’s-related ulcers and fissures penetrate beneath the inner mucosal layer of the intestines.
Anyone with Crohn’s disease can develop iron deficiency in this way. But Marion notes that people who already have a higher risk of iron deficiency to begin with — namely, women of childbearing age, who may lose a significant amount of iron each month in their menstrual blood — are more likely to develop the condition and to develop it more quickly.
Other potential causes of low hemoglobin include vitamin B12 deficiency due to poor absorption in the intestines and anemia of chronic inflammation — a form of anemia, Marion notes, that’s often seen in many chronic and inflammatory disorders.