Persistent tiredness is one of the most common complaints among people living with Crohn’s disease or ulcerative colitis, often dismissed as an inevitable part of having inflammatory bowel disease (IBD). Frequently, though, this fatigue has a specific, treatable cause: iron deficiency, with or without anaemia (a condition where the blood has too few healthy red blood cells to carry adequate oxygen around the body). Understanding why iron deficiency happens so often in IBD can help patients recognise it, discuss it with their care team, and take practical steps towards feeling better.
What is iron deficiency anaemia?
Iron is essential for making haemoglobin, the protein in red blood cells that carries oxygen from the lungs to the rest of the body. When iron stores run low, the body cannot produce enough healthy red blood cells, and oxygen delivery to tissues and muscles becomes less efficient. This is experienced as fatigue, breathlessness, poor concentration, pale skin, and sometimes a fast heartbeat. Iron deficiency can exist before anaemia develops, meaning a person can feel unwell even when a standard blood count still looks borderline normal.
Why it matters for gut inflammation
IBD affects iron levels through more than one pathway, which is why iron deficiency is so common compared with the general population. Ongoing gut inflammation, chronic blood loss from ulcerated tissue, and reduced nutrient absorption in the small intestine can all contribute simultaneously. Because inflammation itself changes how the body handles iron, correcting the underlying gut inflammation is often just as important as replacing iron directly.
Key mechanisms
Chronic blood loss from the gut lining
In ulcerative colitis and Crohn’s disease, inflamed or ulcerated bowel lining can bleed, sometimes visibly and sometimes in amounts too small to notice. Over weeks and months, this slow, ongoing loss depletes iron stores faster than diet alone can replace them. It is one of the most direct and common causes of iron deficiency in IBD, and tends to track with disease activity, meaning flares are often when losses are greatest.
Reduced absorption in the small intestine
Iron is mainly absorbed in the upper small intestine, particularly the duodenum. In Crohn’s disease affecting this region, or following surgery that removes or bypasses part of the small intestine, the absorptive surface area is reduced. Even with adequate dietary intake, less iron may actually enter the bloodstream, creating a persistent shortfall despite reasonable eating habits.
Inflammation and hepcidin
Hepcidin is a liver hormone that regulates how much iron is released from stores and absorbed from food. During active inflammation, hepcidin rises, effectively locking iron away in storage cells and blocking its release into the blood. This normal defence response, thought to limit iron availability to bacteria, can worsen functional iron deficiency in chronic conditions like IBD even when total iron stores are not critically low. This is why levels can improve once inflammation is controlled, sometimes without any change in diet or supplements.
Diet, appetite, and food avoidance
Active symptoms such as abdominal pain, diarrhoea, and nausea often lead people to reduce food intake or avoid iron-rich foods, particularly red meat, if these seem to trigger symptoms. Over time, reduced intake compounds losses already occurring through bleeding and malabsorption, making dietary patterns during flares an important factor to review with a dietitian.
Overlap with other nutrient deficiencies
Iron deficiency in IBD frequently occurs alongside low vitamin B12 or folate, particularly in Crohn’s disease affecting the terminal ileum (the last part of the small intestine, where B12 is absorbed). Because both deficiencies can independently cause fatigue and pale skin, a full nutritional blood panel is usually needed to identify exactly which are present, rather than assuming iron is the sole factor.
It is worth remembering that fatigue in IBD does not always mean inflammation or anaemia are present. Sleep quality, stress, medication side effects, and general deconditioning can all contribute, so persistent fatigue should be discussed with a gastroenterologist or IBD nurse rather than self-diagnosed. Blood tests, including ferritin (a marker of iron stores) and inflammation markers, are needed to confirm what is actually driving the symptom.
Practical Takeaways
- Ask for regular blood tests, including ferritin and full blood count, especially during or after a flare.
- Report new or worsening fatigue to your IBD team rather than assuming it is unavoidable.
- Discuss iron-rich foods, such as lean red meat, poultry, fish, and fortified cereals, with a dietitian if intake has dropped.
- Ask whether oral iron supplements are suitable, since they can sometimes worsen gut symptoms during active inflammation.
- If oral iron is poorly tolerated, ask about intravenous iron, which bypasses the gut and is often preferred during active disease.
- Keep follow-up blood tests scheduled even after symptoms improve, since iron stores can take months to fully replenish.
Conclusion
Iron deficiency and anaemia are common in IBD, but patients need not simply live with them. Recognising that fatigue may have a treatable, measurable cause can shift the conversation from “this is just my IBD” to a focused plan involving blood tests, dietary review, and, where needed, iron replacement. Because inflammation itself affects how iron is absorbed and used, managing the underlying gut disease remains central to correcting iron levels long term. Working closely with a gastroenterology team ensures the right cause is identified and treated appropriately, rather than assuming all tiredness is inevitable.
References
- Gasche C, Lomer MC, Cavill I, Weiss G. Iron, anaemia, and inflammatory bowel diseases. Gut. 2004;53(8):1190-1197. doi:10.1136/gut.2003.035758.
- Dignass AU, Gasche C, Bettenworth D, et al. European consensus on the diagnosis and management of iron deficiency and anaemia in inflammatory bowel diseases. J Crohns Colitis. 2015;9(3):211-222. doi:10.1093/ecco-jcc/jju009.
- Nielsen OH, Ainsworth M, Coskun M, Weiss G. Management of iron-deficiency anemia in inflammatory bowel disease: a systematic review. Medicine (Baltimore). 2015;94(23):e963. doi:10.1097/MD.0000000000000963.
- Weiss G, Goodnough LT. Anemia of chronic disease. N Engl J Med. 2005;352(10):1011-1023. doi:10.1056/NEJMra041809.
- Stein J, Dignass AU. Management of iron deficiency anemia in inflammatory bowel disease: a practical approach. Ann Gastroenterol. 2013;26(2):104-113.
- Kulnigg S, Gasche C. Systematic review: managing anaemia in Crohn’s disease. Aliment Pharmacol Ther. 2006;24(11-12):1507-1523. doi:10.1111/j.1365-2036.2006.03146.x.
This article is intended for informational and educational purposes only. It does not constitute medical advice and should not be used as a substitute for professional medical guidance, diagnosis, or treatment.