Can Iron Cause Constipation? Understanding Iron Supplements and Constipation

Disclaimer: Please note that this article is research based and some of the views and findings do not conform with the CSN Diet.

Few things can spoil your day quite like an episode of constipation. While it’s seldom serious, it affects people of all ages, often when you need it the least.

Constipation can have many causes, and one that is often overlooked is the imbalanced intake of iron.

Let’s take a closer look at the connection between iron and constipation.

Constipation explained

Most of us are probably well aware that constipation is when your bowel movements do not occur as often as they should. 

Further symptoms include hard and small stools, inability to completely empty your bowel as well as feeling bloated.

‘Regular’ means different things for different people. For some it’s normal to go to the loo a few times per day, while a few times per week is sufficient for others. 

It is considered normal not to go longer than three days without a bowel movement.

iron and constipation

Common causes of constipation

It’s hardly a surprise that constipation is such a commonly occurring condition when you consider the large number of things that can cause it.

Your large intestine, or bowel, is made up of your colon and rectum. This is your food’s final destination before it leaves your body again. Here, water is absorbed from digested food, changing it from a liquid to a solid.

When digested food stays in your colon for too long, too much water gets absorbed, changing your stool from soft to hard and dry, making it difficult to push it out of your body.

The many factors that can cause constipation include: 

  • Not enough fibre in your diet
  • A change in your routine or lifestyle
  • Not having sufficient privacy when using the toilet
  • Ignoring the urge to pass stools
  • A sedentary lifestyle
  • Not drinking enough fluids
  • Fever
  • Being underweight or overweight
  • Anxiety and depression
  • Psychiatric issues relating to trauma

In some cases, constipation can be a side-effect of the medication you are taking. Medications that can bring on constipation include:

  • Aluminum antacids
  • Antidepressants and antipsychotics
  • Antiepileptics
  • Calcium supplements
  • Opiate painkillers such as codeine and morphine
  • Diuretics

Sometimes, but less often, constipation can be a symptom of an underlying condition, such as:

  • Irritable bowel syndrome
  • Diabetes
  • Hypercalcaemia
  • Underactive thyroid
  • Muscular dystrophy 
  • Multiple sclerosis
  • Parkinson’s disease
  • Anal fissure
  • Spinal cord injury
  • Pregnancy
  • Bowel cancer

Iron supplements also belong on this list of constipation causes. So how does that work?

The role of iron in your body

Your body needs iron for growth and development. This mineral helps your body to make hemoglobin, a red blood cell protein that carries oxygen from the lungs to the rest of the body.

It also aids in the production of myoglobin, a protein that provides oxygen to your muscles. The production of certain hormones also relies on the presence of iron.

To simplify it, you have iron to thank for keeping your blood healthy

Iron helps to preserve many vital functions in the body, like general energy and focus, gastrointestinal processes, the immune system and the regulation of body temperature.

The connection between iron and constipation

On average, an adult stores between one and three grams of iron in their body. 

Menstruating women need more iron because blood contains about 70% of the body’s iron. At the beginning of the menstrual cycle the body loses around 2 mg of iron per day. 

Before menopause women need 18mg of iron per day. When regular periods become a thing of the past, 8mg per day is sufficient.

It is important to get the amounts right, as your body metabolises iron in a unique way – it doesn’t excrete it, but recycles and retains it instead. For this reason, too much or too little iron in your body can make you ill.

Your body is efficient at keeping your iron levels balanced. The body produces a hormone called hepcidin, which regulates the absorption of iron.

This system works quite well, unless you have an underlying condition that either suppresses or stimulates hepcidin formation.

Iron overload can bring on serious symptoms and be fatal if they are left untreated. Most people aren’t at risk for this, with the most common iron overload disorder being hereditary hemachromatosis.

This condition leads to a build up of iron in tissues and organs, which over time can cause arthritis, cancer, liver problems, diabetes and heart failure.

On the other hand, lower than normal levels of iron leads to iron-deficiency anemia. Symptoms often first go unnoticed, and later on you will start noticing the following:

  • Feeling weak and tired
  • Pale skin
  • Shortness of breath
  • Dizziness
  • Cravings for non-food items
  • Tingling feeling in the legs
  • Pain or swelling of the tongue
  • Cold hands and feet
  • Fast or irregular heartbeat
  • Brittle nails
  • Headaches

Too little iron is a more common problem than too much, with a larger part of the community being at risk. This especially includes women, due to them losing blood via menstrual periods. Other risk factors include:

  • Following a poor diet, or neglecting to replace meat with another source of iron if you are a vegetarian
  • Frequently donating blood
  • People experiencing rapid growth spurts such as teenagers
  • High performance or endurance athletes
  • Adults over the age of 65

Iron shortages are easily treated with iron supplements. It’s best to do this with the assistance of your GP, who will prescribe the correct dosage to prevent you from taking too much. 

You might also be prescribed vitamin C, as it assists with the absorption of iron. In a few months your problem should be sorted, no big deal.

However, it’s with the use of iron supplements that you could run into a new problem. Yes, constipation. In fact, constipation is one of the most common complaints coming from those who take iron supplements.

How do iron supplements cause constipation?

Iron supplements taken orally are the most common way to treat iron deficiency, but 60% of patients experience constipation, sometimes severe, along with abdominal pain and bloating. 

A 2020 review claimed that the mechanisms by which iron causes constipation is unclear.

However, scientists think that an excessive number of iron ions in the stomach cause more water transportation into the intestines. 

This water is then distributed from the lower part of the gastrointestinal system to maintain the acid-base balance. Therefore, not enough water remains in the lower intestines to ensure the softening of stool.

Also, iron supplements generally contain more iron than the body can absorb.

This means that a large amount of iron remains in the gut, affecting the balance of gut bacteria.

What can you do to prevent constipation from iron tablets?

In some cases the constipation is so bad that people would rather just go without treatment for iron deficiency anemia. But, there are steps you can take to lessen the discomfort.

  1. Prevention is better than cure. Simply prevent having to take iron tablets by making sure you are getting sufficient iron in your diet.
    Lean beef, chicken, beans, dark green leafy vegetables, whole grains and nuts are good sources of iron.
  1. Choose the right supplement for your body. If constipation is a concern for you, talk to your GP about a supplement that is gentle on your stomach, as iron supplements come in different forms.
  1. Drink a lot of fluids. Take a full glass of water with each iron tablet to provide your intestines with the fluids it needs to soften stools.
  1. Take your supplements the right way. It could be helpful to start using iron supplements gradually. Start with only half the dosage, and increase it every three days until you reach the full dosage.
    You can also break your tablet into three smaller daily pieces to reduce your likelihood of getting constipated.
  1. Try to get some exercise every day to stimulate healthy bowel movements.
  1. If needed, take a stool softener to relieve constipation. Stool softeners increase the water content in stools, making them softer and easier to pass.
  1. Eat a lot of fruit and vegetables. They contain fibre which adds bulk to stools, making them easier to pass.

Whether you are taking iron tablets or not, if your constipation is paired with rectal bleeding, blood in the stool, vomiting, fever, back pain or unintentional weight loss, it’s time to visit the doctor.

How to not get constipated while taking iron?

To minimize constipation while taking iron supplements, consider the following tips:
1. Start with a lower dose: Begin with a small dose of iron and gradually increase as tolerated.
2. Take iron with food: Although iron is best absorbed on an empty stomach, taking it with a small amount of food can reduce stomach upset and constipation.
3. Stay hydrated: Drink plenty of water throughout the day to help soften stools and promote bowel movements.
4. Increase fiber intake: Eat high-fiber foods such as fruits, vegetables, legumes, and whole grains to help maintain regular bowel function.
5. Exercise regularly: Physical activity can help stimulate bowel movements.
6. Consider a stool softener: If necessary, a mild over-the-counter stool softener might help ease constipation.
7. Try different forms of iron: Some forms of iron supplements, like ferrous gluconate, may be less constipating than others. Chat with your healthcare provider about which form might work best for you.

Does iron tablets cause constipation?

Yes, iron tablets can cause constipation in some individuals. This is because iron supplements can reduce the activity of the GI tract and make stools drier and harder to pass. If you experience constipation while taking iron tablets, consult with a healthcare professional for advice and alternative options.

What are the main causes of constipation?

Constipation can result from a variety of factors including:
Inadequate water intake: Not drinking enough water can lead to hard stools.
Low fiber diet: A diet lacking in fiber can reduce bowel movement frequency.
Lack of physical activity: A sedentary lifestyle can slow down the digestive system.
Medications: Certain medications, like narcotics, antidepressants, and high-calcium antacids can cause constipation.
Ignoring the urge to have a bowel movement: Regularly suppressing the urge can lead to constipation.
Medical conditions: Some health issues like hypothyroidism, diabetes, and irritable bowel syndrome can contribute to constipation.
Stress: High levels of stress can affect the digestive system and lead to constipation.
Aging: As people age, the digestive system can become less efficient.

 How to take iron supplements without getting constipated?

To take iron supplements without getting constipated, follow these steps:
1. Choose the right supplement: Talk to your healthcare provider to find a form of iron supplement that is both effective and gentle on the stomach.
2. Monitor your dosage: Start with a lower dose of iron and increase it gradually as needed under the guidance of your healthcare professional.
3. Timing is key: Take your iron supplement at a time when your stomach is least sensitive, often with a small amount of food.
4. Stay active: Commit to a regular exercise routine to help stimulate digestion.
5. Keep hydrated: Drink plenty of fluids, especially water, to help move waste through your digestive system.
6. Optimize your diet: Incorporate a diverse range of fiber-rich foods into your diet to help maintain healthy bowel movements.
7. Listen to your body: If you’re experiencing gastrointestinal side effects, it’s crucial to discuss this with your healthcare provider who may need to adjust your iron regimen or explore alternative treatments.

Remember, while it’s important to manage constipation, it is also crucial not to compromise iron therapy if you need it. Therefore, working closely with your healthcare provider is the best strategy for maintaining both digestive health and adequate iron levels.


Don’t lose hope, your constipation symptoms should improve long before your course of iron supplements are finished. 

In the meantime, simple healthy living can go a long way in making you feel better. A healthy diet, enough water and sufficient exercise is all you need to improve many conditions, including constipation.



Hi, my name is Karien Nel and today I’m 37kg lighter than the day I started my weight loss journey with CSN Diet.

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3 thoughts on “Can Iron Cause Constipation? Understanding Iron Supplements and Constipation”

  1. Karien môre,ek het ń hoë vlak van ferriten en wil graag twintig kilogram verloor maar nie seker wat van jul produkte om te gebruik nie.Kan jy help asb?


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