Iron Supplements and Constipation: What’s the Link

Your body depends on iron to make red blood cells, which transport oxygen throughout your body. Low iron levels can lead to iron-deficiency anemia, a condition that can impact your body's ability to perform key functions.

Low iron levels can impact your health even if you don't have anemia. Low iron levels are linked to mood changes, fatigue, and trouble concentrating.

You may need to take iron supplements if your iron levels are low or if you have iron deficiency anemia. These supplements can help keep your iron levels in a healthy range. But like any medication, iron supplements can cause side effects, including several stomach symptoms including constipation.

Do iron supplements cause constipation?

Yes, iron supplements can cause constipation, though it's not entirely clear why. Researchers think iron supplements may trigger constipation in two ways:

• Gut microbiome impact: Higher iron levels in your gut may affect your gut microbiome. Some studies suggest that iron may tip the balance of "good" versus "bad" bacteria, allowing harmful bacteria to flourish. This can lead to many gut symptoms, including constipation.

• Increased positive charge: As your body absorbs iron, it creates an extra positive charge inside your gut. To neutralize this charge, your gut absorbs more water. Less water in your gut leads to drier stools that are harder to pass.

But these theories haven't been proven yet, and other factors may also play a role. It may be a while before scientists are able to fully understand why iron can trigger constipation. For now, keep this good news in mind: not everyone who takes iron will develop constipation. In fact, most people don't get constipation when they take iron supplements.

There's more evidence about the iron doses that make you more likely to develop constipation. Studies suggest that taking more than 45 mg of iron per day increases your risk of developing constipation. Many people need to take doses above this cut-off to treat their iron deficiency. But again, not everyone who takes higher doses of iron will develop constipation.

Can iron supplements cause other side effects?

Yes, iron supplements can cause other gut-related side effects in addition to constipation, like:

• Nausea

• Stomach pain

• Gas or bloating

• Diarrhea

• Dark stools

Liquid iron may also cause a metallic taste and can possibly stain your teeth.

How common is constipation from iron supplements?

It's not clear how often people develop constipation while taking iron supplements. In a review of studies, about 12% of people who took iron supplements by mouth developed constipation. But in a clinical study, only 4% of people taking an oral iron supplement developed constipation.

While the exact risk isn't known, most people don't seem to develop constipation while taking iron supplements by mouth. Another piece of good news is that studies suggest you're even less likely to develop constipation if you're receiving intravenous (IV) iron infusions. In one clinical study, fewer than 1% of people developed constipation while receiving IV iron infusions.

How can you lower your risk of developing constipation while taking iron supplements?

It's not clear whether you can lower your risk of developing constipation while taking iron supplements.

Scientists have looked at whether changing iron formulations can impact your risk of developing constipation. Oral iron supplements come in several forms, including:

• Ferrous sulfate

• Ferrous gluconate

• Ferrous fumarate

One study found that people taking ferrous sulfate were most likely to develop gut-related side effects like constipation. But older studies showed that rates of side effects were the same, no matter which form of iron supplement people took.

One study found that people taking extended-release iron were less likely to develop constipation. But other studies didn't show this same benefit.

So, it's not clear if any particular form of iron can prevent constipation. If you do develop constipation while taking iron, consider switching formulations and seeing if that helps. You can also consider switching to a slow-release (or extended-release) iron supplement.

Also, treatments that relieve other causes of constipation may also help with constipation caused by iron supplements. Here are some steps you can take to relieve your constipation:

• Stay hydrated by drinking enough water each day.

• Add fiber-rich foods to your diet.

• Don't wait! Go to the bathroom when you feel the urge to poop.

• Try an over-the-counter (OTC) or prescription laxative.

• Talk to your healthcare team about avoiding other medications that cause constipation.

When should you seek care for side effects from iron supplements?

Talk to your healthcare team if you develop constipation or other side effects while taking iron supplements. Don't stop taking your supplements on your own. This can cause worsening symptoms.

Your team can help you brainstorm solutions so that you can keep taking your supplements and stay constipation-free.