If someone with irritable bowel syndrome (IBS) cannot absorb enough iron from their food, they may develop anemia. However, anemia is not a classic symptom of IBS.

Iron deficiency anemia is a form of anemia that happens when a person’s body does not have enough red blood cells. These cells carry oxygen in the blood, so a person with anemia can feel tired and fatigued.

About one-quarter of the world’s population has anemia, usually due to iron deficiency, and it is particularly prevalent among menstruating individuals. Although anemia is not a standard symptom of IBS, it is not uncommon for it to affect people with this condition.

A 2014 study found that about half of those with the condition may have a mild iron deficiency, suggesting a link between IBS and anemia. People with IBS may develop anemia if they are unable to absorb enough iron from their food.

Keep reading to learn more about the symptoms and diagnosis of anemia and its connection with IBS.

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Anemia means that a person does not have enough red blood cells. Although there are several different forms of anemia, iron deficiency anemia is the most common. It can happen when a person does not get enough iron in their diet, does not absorb enough iron from their food, or has excessive bleeding that depletes their iron stores.

A 2014 study of 217 people with IBS found that about half of them had subclinical iron deficiency. A subclinical deficiency is one in which a person’s iron levels are low but not low enough to constitute true iron deficiency anemia.

Subclinical iron deficiency can cause symptoms similar to those of traditional anemia, such as fatigue, breathlessness, and headaches.

However, the symptoms vary from person to person. Some individuals may have more severe symptoms, while others will have none.

Some people may find that IBS contributes to their anemia. This can happen when the body does not absorb nutrients from food properly.

Difficulty digesting certain carbohydrates and insoluble fiber is common in IBS. Many carbohydrates and fibrous foods, such as breakfast cereals, are fortified with iron. Additionally, many plant-based sources of iron — such as beans, lentils, and leafy greens — are rich in carbohydrate, fiber, or both.

If the body struggles to digest these foods, it might not absorb enough iron. In addition, some individuals may choose to avoid these foods if they aggravate their digestion or cause IBS flare-ups.

However, some people with IBS may develop anemia for unrelated reasons.

As anemia is common, many people with IBS may already have it. Some risk factors for iron deficiency anemia include:

  • pregnancy
  • menstruation
  • insufficient consumption of iron through food
  • bleeding in the gastrointestinal tract
  • blood loss due to heavy periods, injuries, or childbirth

Anemia is more common in people with inflammatory bowel disease (IBD), a chronic inflammatory digestive condition, than in those with IBS. In fact, the co-occurrence of digestive issues and anemia suggests IBD.

People with IBD may develop anemia because of poor nutrient absorption. They may also have low iron because of bleeding in the digestive tract.

Although both IBD and IBS can cause digestive problems, they are distinctly different conditions. IBD is a group of conditions that cause chronic inflammation in the gut. In contrast, IBS is a functional disease with no singular cause.

Most people with low iron do not experience symptoms until their iron levels fall below 7–8 grams per deciliter of blood. By the time a person has symptoms, they may already have been anemic for a long time.

To test for iron deficiency, a doctor may do a complete blood count, test iron levels, and measure ferritin levels.

Some symptoms that can indicate anemia include:

  • unusually pale skin
  • fatigue
  • weakness
  • restless legs
  • shortness of breath

People who have IBS and anemia may wish to discuss with their doctor the best ways to manage their condition.

In some cases, a doctor may previously have misdiagnosed a person as having IBS when they actually have a form of IBD. Tests can determine whether this is the case.

Chronic, untreated IBD can cause malnourishment, bowel damage, and infections. Therefore, it is important to seek a medical evaluation for anemia symptoms that occur alongside digestive issues.

Vitamin B12 deficiency is a nutrient deficiency that can cause macrocytic anemia. This means that the red blood cells are abnormally large and that there are fewer of them than normal.

People following plant-based diets are particularly vulnerable to vitamin B12 deficiencies because the primary way to consume the nutrient is through animal products, such as meat, cheese, and eggs. However, these deficiencies can affect anyone.

Vegans and vegetarians can get vitamin B12 from supplements and fortified foods.

Although some people with IBS may have macrocytic anemia, there is no evidence that IBS increases a person’s risk of vitamin B12 deficiency or that vitamin B12 deficiency causes IBS. A 2020 review including 12,295 participants found that there was no difference in vitamin B12 deficiency rates between people with and without IBS.

Moreover, the study did not find evidence of widespread nutritional deficiencies in people with IBS.

The treatment for anemia usually involves taking an iron supplement. These come in the form of tablets, capsules, or liquids.

If a person has a severe iron deficiency, a doctor may recommend IV iron infusions.

It is also important to check for any underlying causes. A healthcare professional may ask a person to track their food intake to assess how much iron they are consuming.

Here are the answers to some questions people often ask about anemia and IBS.

Can IBS cause blood in a person’s stool?

Blood in the stools is not typically seen in a person with IBS. If a person with IBS is experiencing blood in their stools, they should consult a doctor.

What stomach issues cause blood in stool?

Stomach issues that can cause blood in the stool include:

In the above instances, blood in the stool will look dark and tar-like.

What are some signs of IBS?

Signs that a person has IBS include the following:

Can IBS or IBD cause bleeding?

Whilst IBD can cause blood in the stool, it is not typically seen in people with IBS.

If a person is concerned about blood in their stool, they should talk with a doctor.

Although anemia can occur with IBS, it is more common in people with IBD. However, because anemia is common, it can be unrelated to these conditions.

Treating iron deficiency anemia is fairly simple, and in most cases, a person can expect their iron levels to improve in a few weeks.