Why Iron Supplements May Cause Your Stool to Look Black

It's a sight that can be quite alarming the first time it happens: you look down into the toilet after a bowel movement and are shocked to see your stool is black or at least very dark brown. While it may look like you're experiencing some sort of internal bleeding or blockage, chances are if you've recently started taking an iron supplement, the culprit is actually that simple. The high iron content from the supplement is likely leading to blackened stool.

Although seeing black stool can understandably cause concern, the discoloration is actually harmless in most cases. As iron is a standard mineral found in blood and critical for healthy cells, having more of it from a supplement often manifests as extra black/brown pigment. Understanding why iron turns feces black and how to manage any annoying side effects can help you get the benefits of supplementation without too much bathroom drama.

What Are Iron Supplements?

Iron is an essential mineral that plays many important roles in the body, like transporting oxygen in the blood and assisting with energy production. Most people get enough iron through their regular diet. Good food sources include red meat, seafood, beans, spinach, and iron-fortified cereals.

However, certain groups have higher iron needs or trouble absorbing iron. These include pregnant women, infants and teenage girls, athletes, frequent blood donors, and those with gastrointestinal disorders. Iron deficiency can lead to fatigue and anemia. To prevent or treat low iron, doctors may recommend oral iron supplements such as ferrous sulfate or ferrous gluconate.

Reasons for Iron Supplementation

• Pregnancy - increased iron needs for mom and baby
• Heavy menstrual bleeding - higher loss of iron
• Gastrointestinal disorders - decreased absorption from food
• Strict vegetarians or vegans - decreased iron in diet
• Growth spurts in adolescents
• Frequent blood donation
• Iron deficiency anemia

While getting iron from whole food sources is ideal, supplements offer a concentrated amount that is absorbed more readily. Most provide 20-65 mg elemental iron per dose, much higher than the 18 mg daily recommendation for adult men and women.

How Iron Supplements Cause Black Stool

There are a few reasons why excess iron from supplements can lead to blackened feces:

Iron Naturally Coloring Stool

Iron has an innate black/brown pigment. This is why blood in stool also causes very dark or black coloring. The bilirubin in bile, which helps digest fats, also contributes a brownish hue. Having a higher concentration of iron in the intestines from supplements simply provides more pigment to turn stool very dark brown or blackish.

Increased Absorption of Iron

Normally the body only absorbs a small percentage of iron from food, about 10-20%. But iron supplements use forms like ferrous sulfate that are more readily absorbed, often at least 30% up to 50%. With more iron getting absorbed into the bloodstream, less remains behind in the intestines to color the stool black.

Dose and Formulation

The dose and type of iron supplement impacts stool color changes too. Standard doses of 50-100 mg/day are more likely to cause blackness than smaller 15-25 mg doses. Formulations that release slowly over time can minimize drastic pigment changes. Quick-absorbing forms like ferrous sulfate lead to black stool faster.

Is Black Stool From Iron Dangerous?

While disconcerting at first glance, black or really dark stool caused by iron supplements is harmless in most cases. As long as the feces is solid and there are no other concerning symptoms, it simply indicates the excess iron is being excreted. However, there are a few instances where black stool warrants more investigation:

Diarrhea or bloody stool

Severe diarrhea or obvious blood mixed with blackish stool could signify an underlying health condition like an infection, inflammation, or bleeding in the GI tract. See a doctor right away if these symptoms develop.

Started before taking supplements

Black stool that occurs suddenly but began before starting iron supplementation would be more suspicious. Bleeding in the stomach or intestines from an ulcer, polyp, or cancer can appear black and tarry.

Anemia persists

If you still have iron deficiency anemia and symptoms like exhaustion despite taking supplements and getting black stool, poor absorption may be preventing the iron from being utilized properly. See your healthcare provider for additional testing.

Tips for Taking Iron Supplements

To get the benefits of iron supplements while minimizing bathroom surprises, keep these tips in mind:

Start with a low dose

Begin with 15-25 mg iron per day and gradually increase to 50-100 mg if needed. This allows the body to adjust and avoid sudden pigment changes.

Take with vitamin C

Vitamin C enhances iron absorption, allowing you to take a lower dose with fewer side effects like black feces.

Avoid calcium and antacids

Calcium and antacids interfere with iron absorption. Space your iron dose away from these.

Take on an empty stomach

Consuming iron supplements with food can cause GI upset but also decreases absorption. Take on an empty stomach with water.

Stay hydrated

Getting enough fluids helps soften stool to pass more easily. Prunes or prune juice are natural laxatives.

Seeing black stool after starting iron supplementation can seem jarring and concerning. However, in most cases it is a harmless side effect that provides visible proof the iron is being absorbed properly into your system.

Focus on the benefits of correcting an iron deficiency, while monitoring for any severe side effects. With time, the body will adjust to the influx of iron and stool color changes should stabilize. Just be prepared for your bathroom experience to get a little Gothic until your system gets used to the influx of all that productive yet sinister-looking iron.