The Link between IBS, Anemia, Low Iron, And Iron Supplements.


Quick insights:

IBS doesn’t cause anemia, and anemia is not a symptom of IBS. The presence of anemia with IBS requires consultation of your doctor about the causes of anemia with IBS. Both anemia and IBS are common conditions, their co-existence doesn’t necessarily mean they are related.

Possible causes of anemia with IBS:

Some conditions can cause anemia and have symptoms similar to IBS, such as:

  • Celiac disease.
  • Inflammatory bowel disease.
  • Diverticular disease.
  • Peptic ulcer disease and H. Pylori infection.
  • Diverticular disease.

Does IBS cause anemia?

Irritable bowel syndrome is a functional gastrointestinal disorder. “Functional” Means we (doctors) couldn’t find a definite lesion inside your digestive system. Anemia is not a symptom or a result of IBS. Furthermore, the ROME IV criteria for  IBS diagnosis consider anemia with IBS is a “red flag” sign.
Anemia is something else inside your gut (other than IBS). Also, anemia can be a random association with your IBS. Because both anemia and IBS are very common conditions:
  • Irritable bowel syndrome affects about 15% of the entire population. It ranges from 10 to 25% in different communities (ref).
In conclusion, IBS is not a cause of anemia. The presence of anemia with IBS requires more investigation by your doctor. This is important to exclude conditions that mimic IBS.
What does it mean to have anemia with IBS?

1- Separate causes of anemia and IBS.

The most common scenario is to have both anemia and IBS. As we explained before, they are both common. Having both IBS and anemia doesn’t mean they are related. Each can affect you due to a separate cause. The only link in this condition is time.
Common causes of anemia include (ref):
  • Iron Deficiency anemia. It is the most common. IDA occurs due to a shortage of iron intake or increased blood loss.
  • Vitamin deficiency anemia. It is usually caused by folic acid and vitamin B-12 shortage.
  • Anemia of inflammation. Any chronic inflammatory state, such as chronic infections (as HIV), cancers, and autoimmune diseases (such as Rheumatoid Arthritis), will lead to anemia.
  • Other (less common). Such as Aplastic anemias, Hemolytic anemias, and sickle cell anemia also can occur.

2- IBS-like disease causing anemia.

IBS is a “functional” disease. We (doctors) diagnose IBS based on some clinical criteria (symptom-based diagnosis). Until this moment, no specific test or investigation can diagnose IBS.
You can consider IBS as a diagnosis of exclusion.
Also, the symptoms of IBS are not specific. Abdominal pain, diarrhea, constipation, and bloating are common across all diseases affecting your gut.
So, attributing vague conditions of your gut tract to IBS is common. For example:
  • Celiac disease affects IBS patients more than the general population (ref).
  • Up to 50% of patients with IBS diarrhea have “Bile acid diarrhea” (ref, ref).
So, a false-positive diagnosis of IBS is common. And the presence of anemia should raise the question about your IBS.
Your doctor is the only person who can tell if it is IBS or an IBS-like disease causing anemia.
Common IBS-like conditions causing anemia include:
  • Celiac disease.
  • Inflammatory bowel disease.
  • Diverticular disease.
  • Colon cancer.
  • Peptic ulcer disease and H. Pylori infection.
  • Diverticular disease.

Most common IBS-like conditions that cause anemia.

Before we dive into conditions mimicking IBS, you should read how IBS is diagnosed.
In summary, IBS is a functional disease characterized by recurrent abdominal pain, which:
  • Occurs at least one day per week for the last 3 months.
  • The onset of pain should be from 6 months or more.
  • Abdominal pain is related to at least 2 of the 3:
1- Defecation.
The abdominal pain either decreases or increases after a bowel movement.
2- Stool form.
The onset of pain is associated with changes in the form of stool. The stool becomes either harder or more loose (or even watery).
3- Stool frequency.
The onset of pain is associated with a change in stool frequency. The bowel movements become more frequent (diarrhea) or less frequent (constipation).
But these symptom-based criteria can confuse doctors with other gut diseases. Out of the too many diseases that mimic IBS, we selected the most common and the most likely to cause anemia:

1- Celiac disease.

Celiac disease is a common disease affecting 0.5 to 1% of the population (ref). It occurs due to sensitivity to a protein in wheat and barley called (gluten).
Celiac disease has symptoms resembling IBS-diarrhea as:
  • Recurrent diarrhea, which can be severe or persistent.
  • Abdominal cramps.
  • Mucus in the stool.
  • Bloating.
Celiac disease is an actual inflammation in the lining of your small intestine. This true damage leads to symptoms and signs that are not found in IBS.
Symptoms that differentiate celiac from IBS:
  • Presence of Anemia (can be severe).
  • Weight loss. 
  • Presence of actual damage in biopsies taken from the duodenum or small intestine. With IBS, everything is normal.
  • Your doctor can diagnose celiac by blood testing or taking a biopsy from your intestinal wall.
  • It improves or even resolves with a gluten-free diet.
Celiac disease is one of the most common causes of anemia and IBS-like symptoms. Always work with your doctor to investigate the cause of anemia with IBS symptoms.

2- Inflammatory bowel diseases (Crohn’s and Ulcerative colitis).

Inflammatory bowel disease is an immune-mediated condition. IBD causes inflammation and ulcers inside your gut. It can involve the colon only (Ulcerative colitis) or any part of the gut tract (Crohn’s disease).
People with undiagnosed IBD can be treated as IBS patients. This is especially common with mild forms of IBD.
Similarities between IBS and IBD symptoms:
  • Abdominal pain.
  • Diarrhea.
  • Bloating and distension.
  • Mucus in the stool.
Differences (IBD symptoms that are NOT found in IBSS).
  • Anemia. IBD can cause anemia due to the malabsorption of nutrients and bleeding from gut ulcers.


  • Blood in stool and anorectal bleeding is common with IBD.

  • Fever.

  • Weight loss.

  • Extra-abdominal symptoms such as skin rashes and joint problems.

3- Colon cancer.



Colon cancer is a common cause of unexplained anemia. We previously explained the differences between IBS and colon cancer in this article.

Being older or having a family history of coloanorectal cancer raises the risks of having it.]. The Triad of IBS-like symptoms, the onset of symptoms above 50, and anemia should raise the suspicion of colon cancer.

Bleeding from colon cancer can occur without gross blood or black stool. Chronic minute bleeding from the cancer mass can cause anemia.

Interestingly, abdominal pain is not an essential symptom of colon cancer. Instead, a change in bowel habits is far more common with colon cancer.

To make it more clear, here is the frequency of symptoms per 100 patients with coloanorectal cancer (ref):

1- Changes in bowel habits (diarrhea or constipation): in 75% of coloanorectal cancer patients.

2- Red or black blood in stool: in 50%

3- A sense of anorectal mass: 25%

4- Anemia (iron deficiency anemia): present in 10% of coloanorectal cancer patients.

5- Abdominal pain is found in only 3.8% of coloanorectal cancer patients.

Having IBS symptoms and unexplained anemia is a reason to seek medical help. Usually, your doctor will ask you to perform a colonoscopy and endoscopy to rule out the causes of anemia inside your gut. This includes colon cancer, polyps, celiac disease, diverticular disease, and others.


4- Peptic ulcer disease/H.Pylori infection.


The typical presentation of peptic ulcer disease and H. pylori infection is pain in the upper central part of your abdomen. However, many patients may experience symptoms that mimic IBS such as:

H. Pylori is a common organism that infects your stomach lining. It can cause inflammation and ulceration of the stomach. This can end with ulcer formation and bleeding.

Bleeding causes blackish stool or vomiting of blood. In many cases, the bleeding is too small to be noticed but prolonged enough to cause anemia.

Always discuss the possibility of peptic ulcer disease with your doctor. The condition requires a more accurate evaluation by your doctor.

Learn more about peptic ulcer bleeding here.


5- Diverticular disease.


Diverticula are small bulging pouches forming in the digestive system’s lining. They usually affect the lower part of the large intestine (colon). They are common (affect around 20% of people, especially in older ages (ref).