How to Manage Constipation Side Effect of Iron Supplements

written by Dr. Bolanle Aina - Jan 24, 2022
medically reviewed by Dr. Tolulope Olabintan, MD - Mar 1, 2022

Photo Credit: by Sora Shimazaki,
Photo Credit: by Sora Shimazaki,

Anemia is a serious global public health problem that particularly affects young children and pregnant women. WHO estimates that 42% of children less than 5 years of age and 40% of pregnant women worldwide are anemic. Iron-deficiency anemia is most common in patients who have greater needs such as children and pregnant women and in people who may be losing more blood than normal such as in pre-menopausal women and in patients with inflammatory bowel diseases. Iron-deficiency anemia occurs when there is insufficient iron in the body to produce hemoglobin. Hemoglobin is required to make red blood cells that carry oxygen around the body. Inability to circulate sufficient oxygen around the body leads to the fatigue and other symptoms of iron-deficiency anemia.

What are the symptoms of Iron-Deficiency Anemia?

It is possible to be anemic with no significant symptoms. However, when symptoms occur, the most common symptoms of iron-deficiency anemia are tiredness, paleness, fast heartbeats, dizziness, headache, moodiness or even erectile dysfunction. If you ever find yourself feeling any of these symptoms, it is important to check with your doctor to get your iron levels checked and to rule out any other possible causes. Once your doctor determines that your iron is low, based on your lab test results, the doctor may prescribe you some iron supplements or direct you to the pharmacy. After taking iron supplements for 3 months be sure to return to your doctor to check if your iron levels have been normalized. Having too much iron is equally harmful.

What are the main causes of low iron?

Iron deficiency may be caused by 2 main reasons. First, low iron intake from diet and/or inability to properly absorb iron may lead to iron deficiency. Secondly, blood loss via heavy menstruation in women, bleeding ulcer, blood donation e.t.c. may also contribute to low iron levels.

What are the different types of iron supplements?

Iron supplements may be administered as oral or injectable products. Injectable iron is usually reserved for a more complicated cases of iron deficiency. The most commonly used form of iron supplements are the oral drugs since they are generally effective, readily available, inexpensive, and safe.

There are 3 common iron salts: Ferrous gluconate, Ferrous sulphate, Ferrous fumarate giving 35 mg, 60 mg and 100 mg elemental iron per tablet respectfully.

Iron supplements can also be classified as heme and non-heme iron. Heme iron is more readily absorbed than the non-heme iron sources. Better absorption profile of heme iron supplements makes them a potentially better option to avoid related side effects e.g. Hemeboost. Please note that heme iron is usually derived from animal sources, so may not be an ideal option for vegetarian patients.

What are the common side effects of iron pills?

When it comes to iron supplementation, constipation is one of the major side effects. Other side effects include stomach upset, nausea, metallic taste, heartburn or even diarrhea. Your doctor may recommend taking a stool softener such as Colace or a bulk forming laxative like Metamucil to reduce constipation side effects. Another side effect from iron pills is that iron can cause you to have dark stools. The dark color is mainly coming from unabsorbed iron.

Which iron supplement causes less constipation?

First it is important to know: why does iron cause constipation? Constipation due to iron supplementation is caused by unabsorbed iron in the gastrointestinal tract. Therefore, the better iron absorption, the less unabsorbed iron and thus the less constipation side effects. Some studies have shown that unabsorbed iron feeds the growth of bad bacteria in the gut, which may lead to gas, bloating and constipation.

Apart from heme iron, other iron formulations that may cause less constipation and other stomach side effects include: polysaccharide iron, carbonyl iron, iron amino acid chelates, ferrous bisglycinate.

How to manage constipation when taking iron supplements?

The higher the iron dose, the higher the likelihood of side effects such as constipation, stomach upset and nausea. To avoid this,

• Start with a low dose and go up slowly

• Take iron supplements with a full glass of water (8 ounces). Eat lots of fruits, vegetables and fibre rich diet and drink lots of fluids throughout the day. The fruit pear is a great fruit to make a daily part of your meal as it helps with constipation.

• Take iron pills every other day (note that it may take longer to correct the iron deficiency).

• Take a stool softener such as Colace if needed.

• Regular exercise

• Switch to another iron pill that may cause less side effects.

What other conditions can promote constipation

Pregnancy, irritable bowel syndrome, elderly (>65 years), inactivity, use of certain medications such as anticholinergics, calcium channel blockers and opioids.

How to improve iron absorption from supplements?

Although iron is best absorbed on an empty stomach, it causes stomach upset and nausea when taken this way. You may need to take iron pills with food to avoid stomach upset side effect. To improve iron absorption, avoid taking iron with milk, dairy, calcium or antacids. It is also recommended to take iron with vitamin C or orange juice to enhance iron absorption.

Other ways to raise your iron levels is to eat more Iron-rich food products such as meat, poultry, seafood, beans, dried foods (raisins), fortified cereal. Furthermore, it will be best to avoid taking iron with other medications that can affect its absorption. For example, drugs like antacids, antihistamines and proton pump inhibitors may decrease the absorption of iron.

Although prescription is not needed to purchase iron supplements, it is important to take iron only under the doctor’s supervision. Get the doctor to check your iron levels to confirm the need to start or continue supplementation. Ask your pharmacist about your options when it comes to iron supplements.



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While the above article is based on thorough research, we do not claim to offer a substitute for medical advice from a qualified healthcare provider. The article was written for information and educational purposes only. We aim to provide helpful information to our readers, but cannot provide a treatment, diagnosis, or consultation of any sort, and we are in no way indicating that any particular drug is safe or appropriate for you and your individual needs. To receive professional medical attention, you must see a doctor.