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Medically Reviewed

Why Iron Supplements Can Cause Constipation (And How to Prevent It)

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Iron supplements can help people who need more intake. While iron supplements are often associated with constipation, the form of iron makes a difference.

Iron is naturally present in many foods, added to some food products, and available as a dietary supplement. It is essential in many functions in the body including keeping healthy oxygen levels, hormone synthesis, and more. Keep reading to find out why iron supplementation may benefit you and how to prevent constipation often associated with iron supplements.

Why you might need an iron supplement

There are numerous reasons why you might need an iron supplement. One such example is for those eating plant-based diets. In food, iron comes bound in either the heme form in animal products or in the non-heme form in plant sources. Heme iron is more easily absorbed in comparison to non-heme iron and is the most efficiently absorbed source of iron overall.

Red blood cell formation requires iron. Therefore, additional iron is needed for people who menstruate and those with iron deficiency anemia in which the number of red blood cells is low or the blood cells have insufficient levels of hemoglobin.

For those who menstruate, the recommended daily allowance (RDA) of iron is 18 mg with additional needs for those who experience heavier menstrual bleeding. This increases to 27 mg of iron for those who are pregnant. Otherwise, the RDA is between 8-18 mg depending on age and sex.

Iron absorption in the gut is dependent on healthy digestion. Iron supplements can be helpful for those with digestive issues that disrupt iron absorption.

Forms of iron

There are various non-heme forms of iron in dietary supplements. Supplement forms include the following:

  • ferrous sulfate (usually in tablet form)
  • ferrous gluconate (usually in liquid form)
  • ferric citrate
  • ferric sulfate
  • ferrous bisglycinate

Note: “ferrous” and “ferric” both refer to iron of varying atomic structures. Ferrous iron is more bioavailable than ferric iron.

Studies show that iron bisglycinate is absorbed better and can increase iron levels at smaller doses than the common ferrous sulfate form.

Care/of’s iron supplement contains iron bisglycinate, a chelated form of iron. Chelation prevents the mineral from interacting with other compounds, making it easier for the body to digest than non-chelated minerals.

Do iron supplements cause constipation?

Oral iron supplementation has the potential to cause constipation. Some studies suggest iron in supplement form can increase the production of methane gas in the gut, which is associated with the potential for constipation.

However, side effects of iron supplementation may depend on dosage and form of iron. More absorbable forms of iron usually cause less constipation.

Tips to prevent constipation

To help prevent constipation from iron supplements, begin taking your iron supplements in smaller doses and increase gradually over several days until you reach your recommended dosage.

Taking iron supplements along with a source of vitamin C can help you to better absorb the iron and reduce the potential for constipation and gastrointestinal upset.

Our Care/of Iron includes calcium and magnesium ascorbate — buffered forms of vitamin C. These buffered forms combine a highly absorbable form of vitamin C with the minerals calcium, potassium, and magnesium, and help the body absorb iron at a faster rate.

Tips to relieve constipation

If you experience constipation from iron supplementation, consider reducing your dosage of iron or try taking smaller doses spread throughout the day.

While iron is best taken on an empty stomach or in between meals (usually at least 30 minutes before or 2 hours after meals), iron supplements can be taken with a small snack if you experience stomach upset from iron.

Also consider switching to an iron supplement that contains a more bioavailable form of iron, like iron bisglycinate, as outlined above.

H2: Other potential side effects of consuming iron Most potential side effects from supplementing may include digestive upset including nausea, upset stomach, cramps, and constipation.

Iron supplements can reduce calcium absorption and should be taken away from calcium supplements.

When not to take iron supplements

Iron supplements may interact with certain medications and should always be discussed with your prescribing practitioner. Avoid iron supplements if you have excessive levels of iron in your blood. Always get blood levels checked before supplementing with iron. Excessive iron can also be dangerous, so speak to your healthcare provider about appropriate dosage for your needs.

When to speak to a healthcare professional

Talk to your healthcare provider if you experience signs of anemia (including fatigue, weakness, cold hand and feet, and dizziness) or heavy menstrual bleeding, as these may be reasons to need iron supplementation.

Always get your blood levels of iron checked before beginning an iron supplement.

Final takeaways

While iron supplements can sometimes cause constipation, the type of iron supplement can make a difference. Iron bisglycinate is well absorbed with less side effects, and taking a source of vitamin C with your iron supplements can help absorption and lessen uncomfortable side effects.

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