The short answer:
Yes, the administration of iron supplements could cause diarrhea.
Iron supplements are reported to increase or decrease your bowel movements. You may suffer from diarrhea or constipation following the administration of iron supplements.
- Iron supplements are used to treat iron deficiency anemia, your body uses iron to form hemoglobin which carries oxygen to your body.
- Iron supplements are best to be taken with less amount of food for optimum absorption.
- It is advised to avoid taking iron supplements with calcium-containing medications and fiber or calcium-rich foods for maximum absorption of iron.
- Oral administration of iron supplements is commonly associated with gastrointestinal side effects.
- Studies reported both diarrhea and/ or constipation following iron supplements.
- The alteration of bowel movements with iron supplements is attributed to the unabsorbed iron which could lead to alteration in the intestinal micro-bacteria.
- In case you experienced constipation with iron supplements, drinking plenty of water and trying physical activities could help to improve your bowel movements.
- It is advised to take iron supplements with small meals if you experience diarrhea following iron supplements.
What are the main uses of iron supplements?
Iron supplements are necessary for the formation of healthy red blood cells. Your body uses iron to form hemoglobin which carries oxygen to your body. Iron supplements are most important following blood loss and for pregnant women.
According to the National Institute of Health, about 18% of Americans take iron supplements. This includes about 60% of breastfeeding and 72% of pregnant women.
Iron supplements are used in the form of ferrous fumarate, ferrous sulfate, ferrous gluconate, and other forms.
It is available in the form of tablets, capsules, injections, and liquid dosage forms.
What is the best way to take iron supplements?
Iron is best absorbed when it is administered on an empty stomach, however, it commonly leads to stomach upset. Therefore, it is advised to take iron supplements with less amount of food to optimize absorption and minimize stomach upset.
The absorption of orally administered iron supplements is strongly affected by other medications and foods rich in calcium.
You should avoid taking iron supplements with the following medications and foods (Ref).
- Calcium-containing drugs
- Foods rich in calcium such as dairy products
- Fiber-rich foods
- Caffeinated beverages
- Foods containing caffeine
Can iron supplements cause diarrhea?
Iron supplements may increase or decrease your bowel movements. You may have diarrhea or constipation following the administration of iron supplements.
In fact, the side effects of iron supplements are rare to occur. However, the side effects of iron supplements are commonly related to the gastrointestinal tract, especially with patients taking large doses.
The most common side effects of iron supplements include the following:
- Abdominal cramps
- Filling sick
You may have all these side effects at once, however, it is not common to occur.
Reports showed that iron supplements could lead to diarrhea and/or constipation.
A review published in 2015 in the Journal of PLOS showed that:
- 27 studies reported constipation in 12 % of people taking iron supplements.
- 25 studies reported diarrhea in 8% of participants who take iron supplements.
- 30 studies showed nausea as a side effect of iron supplements administration with 11 % of participants affected.
A 2017 randomized study reported the following:
- Among non-dialysis-dependent patients with chronic kidney disease, gastrointestinal side effects were the most common side effects of the treatments with iron supplements (ferric citrate).
- Diarrhea was reported in 20.5 % of patients, while constipation was reported in 18.8 % of patients.
- The gastrointestinal side effects associated with iron supplements commonly appear with large doses of iron.
Why do iron supplements may cause diarrhea and/or constipation?
Scientists attributed iron supplements-induced diarrhea or constipation to the accumulation of unabsorbed iron in the intestinal lumen. Only 20% of the administered dose is absorbed and the remaining amount passes into your intestinal tract. The accumulated unabsorbed iron could lead to alteration in the intestinal micro-bacteria.
A study published in the Journal of clinical nutrition confirmed the alteration of intestinal micro-bacteria by administering iron supplements.
- This study reported a decrease in the number of lactobacilli (beneficial intestinal bacteria) and an increase in enterobacteria (pathogenic bacteria) in the group of patients treated with iron supplements for 6 months.
- This indicates gut inflammation which is associated with changes in bowel movements.
Similar results were reported in another study which reported an increase in gut pathogens that could lead to gut inflammation and diarrhea in patients treated with iron for four months.
How to improve constipation and diarrhea associated with iron supplements:
In case you have constipation following iron supplements:
- Drink plenty of water with iron supplements.
- Try physical activity to improve your bowel movements
- You have to ask your doctor about an appropriate stool softener to reduce constipation.
In case you experienced diarrhea with iron supplements:
- Take iron supplements with a small amount of food.
- Probiotics could help you to reduce or eliminate diarrhea. Yogurt is a probiotic-rich diet.
Other side effects of iron supplements
Your stool color may be changed into black color (dark green or dark chocolate) with iron supplements.
This does not indicate blood in stool, the black color of stool is attributed to unabsorbed iron in your bowel.
Colorization of your teeth
Colorization of your teeth is more common with the liquid dosage form of iron supplements.
It is better to use a straw to avoid this side effect or mix the drug with fluid as juice or use your toothbrush after taking your medication.
1. When should I take iron supplements in the morning or at night?
Iron supplements may lead to nausea and stomach upset. Therefore, it may be better if you take iron supplements at night just before bed to avoid the discomfort sensation of stomach upset.
In contrast, other points of view suggest that taking iron supplements is best early in the morning one hour before your breakfast or with a little amount of food. This point of view is based on the fact that iron supplements are best absorbed when they are administered on an empty stomach.
Accordingly, you can take iron supplements either in the morning or at night. In case you experienced stomach upset, you can take it at night before bed and 2 hours after your meal.
2. Can I take iron supplements every day?
If you have iron deficiency anemia, it is safe to take oral iron supplements every day. However, higher doses of iron are harmful and you should ask your doctor about the optimum dose.
Interestingly, a study published in 2017 showed that taking iron supplements every other day leads to better iron absorption. Accordingly, it is OK to take iron supplements every other day.
3. Should I stop taking iron supplements if my stool is black?
No, you shouldn’t worry about a dark stool with iron supplements.
The dark stool is not a harmful side effect and occurs normally with iron supplements administration. It doesn’t mean blood in the stool. However, this color is due to the non-absorbed amount of iron in your bowel.
4. How long does stool stay black after taking iron?
The dark stool is a normal sign with oral iron supplements.
It may start a few days after starting the oral administration of an iron supplement and may last as long as you still it.