Why Does Iron Cause Constipation

Iron is an essential mineral that plays a crucial role in the production of red blood cells, which are responsible for carrying oxygen throughout the body. Iron is found in many foods, including meat, poultry, fish, beans, and leafy green vegetables. However, some people may need to take iron supplements to meet their daily requirements.

While iron supplements can be beneficial for people with iron deficiency anemia, they can also cause constipation. Constipation is a common side effect of iron supplements, and it can be uncomfortable and even painful. The reason why iron causes constipation is not fully understood, but there are several theories.

One theory is that the high amount of iron in the stomach from supplementation causes an osmotic effect that pulls water into the stomach and away from the lower gastrointestinal system. As water leaves the lower GI tract, stools can become dehydrated, harder, and smaller, ultimately making them more difficult to pass. In this article, we will explore why iron causes constipation and what you can do to prevent or alleviate this uncomfortable side effect.

Iron Absorption in the Body

How Iron is Absorbed

Iron is an essential mineral that the body needs to produce hemoglobin, a protein in red blood cells that carries oxygen throughout the body. The body absorbs iron from food and supplements in the small intestine. Iron can be found in two forms: heme iron and non-heme iron. Heme iron is found in animal products such as meat, poultry, and fish. Non-heme iron is found in plant-based foods such as beans, lentils, and spinach. The absorption of heme iron is more efficient than non-heme iron. Heme iron is absorbed directly into the bloodstream, while non-heme iron requires an additional step to convert it into a form that the body can absorb. Vitamin C can enhance the absorption of non-heme iron, while calcium, phytates, and polyphenols can inhibit its absorption.

Factors Affecting Iron Absorption

Several factors can affect the absorption of iron in the body. These include:

  • Diet: A diet rich in heme iron and vitamin C can enhance iron absorption, while a diet high in calcium, phytates, and polyphenols can inhibit it.
  • Gastric acid: Adequate levels of stomach acid are necessary for the absorption of non-heme iron.
  • Iron status: The body regulates iron absorption based on its iron stores. When iron stores are low, the body increases absorption, and when they are high, it decreases absorption.
  • Age: Infants, children, and pregnant women have higher iron requirements and absorb more iron than adults.
  • Medications: Certain medications such as antacids and proton pump inhibitors can inhibit iron absorption.

It is important to note that iron supplements can cause constipation because the absorption of iron is weak. On average, only 10% of iron from food is absorbed by the body for women and 5% for men. In case of iron deficiency, absorption increases up to 20%. Iron not absorbed by the body feeds bad pathogenic bacteria and causes constipation.

Iron and Constipation

How Iron Causes Constipation

Iron is an essential mineral that is required for the proper functioning of the body. It is involved in the production of hemoglobin, a protein in red blood cells that carries oxygen throughout the body. However, when taken in supplement form, iron can cause constipation as a side effect.

Iron supplements are known to be constipating because they can slow down the movement of stool through the intestines. Iron can also cause the stool to become hard and dry, making it difficult to pass. This is because iron is not easily absorbed by the body, and excess iron can accumulate in the intestines, leading to constipation.

Who is at Risk for Iron-Induced Constipation

Iron-induced constipation can affect anyone who takes iron supplements, but some people may be more at risk than others. Those who are already prone to constipation or have a history of gastrointestinal problems may be more likely to experience constipation when taking iron supplements. Additionally, older adults and pregnant women may be more susceptible to iron-induced constipation.

It is important to note that not everyone who takes iron supplements will experience constipation. The severity and frequency of constipation can vary depending on the individual and the type of iron supplement being taken. It is always recommended to consult with a healthcare provider before starting any new supplement regimen.

Preventing Iron-Induced Constipation

Dietary Modifications

One way to prevent iron-induced constipation is to make dietary modifications. Eating a diet rich in fiber can help regulate bowel movements and prevent constipation. Foods that are high in fiber include fruits, vegetables, whole grains, and legumes. Drinking plenty of water throughout the day can also help prevent constipation.

It is important to note that certain foods can actually inhibit the absorption of iron. For example, calcium-rich foods like milk, cheese, and yogurt can interfere with the absorption of iron. Therefore, it is best to avoid consuming calcium-rich foods at the same time as iron supplements or iron-rich foods.

Supplemental Measures

There are also supplemental measures that can be taken to prevent iron-induced constipation. One option is to switch to a different type of iron supplement. Iron bisglycinate is a well-absorbed form of iron that is less likely to cause constipation than other forms of iron.

Another option is to take a stool softener or laxative along with the iron supplement. This can help prevent constipation and make bowel movements easier. However, it is important to speak with a healthcare provider before taking any supplemental measures to prevent constipation.

Finally, it is important to take iron supplements as directed by a healthcare provider. Taking too much iron can lead to iron toxicity, which can cause serious health problems. Therefore, it is important to follow the recommended dosage and duration of iron supplementation.


Iron is an essential mineral that plays a vital role in human health. However, iron supplements can cause constipation, which can be debilitating for many people. The cause of constipation is the iron itself, not any added ingredient.

To avoid constipation, it is essential to drink plenty of fluids, such as water or orange juice, with each iron pill. Orange juice contains vitamin C, which helps with the absorption of iron. It is also crucial to increase fiber intake and be more active. Exercise is a natural way to stimulate bowel movement and prevent constipation.

If you must take a daily multivitamin or dietary supplement containing iron, consider taking ferrous gluconate, which is less constipating for many people. It is also essential to consult a healthcare professional before taking any iron supplements, especially if you have a history of constipation or other digestive issues.

Overall, iron supplements can cause constipation, but there are ways to prevent and manage this side effect. By staying hydrated, increasing fiber intake, and being more active, you can ensure that you get the iron you need without experiencing debilitating constipation.

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About the Author Adam

As a health and fitness writer, Adam combines his two passions—weightlifting and writing. With a creative writing degree under his belt, he spends his mornings lifting weights, his nights putting pen to paper, and eating too many snacks in between.

Health Disclaimer

  • Any products written about is not intended to diagnose, treat, cure, or prevent any disease.
  • Results may vary/may not be typical. 
  • This information does not constitute medical advice and it should not be relied upon as such. Consult with your doctor before modifying your regular medical regime.


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