Rectal bleeding refers to bleeding from the lower portion of the colon or the rectum, which is the last few inches of the colon. You may notice it as ribbons of red blood mixed in with your stool, blood on toilet paper or pink-colored water in the toilet after you have a bowel movement. Iron supplements may contribute to rectal bleeding. If you experience rectal bleeding, stop taking iron supplements and call your doctor right away.
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Causes of rectal bleeding include anal or colorectal cancer or polyps, anal fissures, Crohn’s disease, ulcerative colitis, celiac disease, diverticulosis, ischemic colitis, radiation-induced colitis, infections, injuries from anal intercourse, severe diarrhea, hemorrhoids and constipation. Iron supplements may cause rectal bleeding indirectly by triggering constipation or diarrhea. Iron supplements also contribute to rectal bleeding related to other conditions by worsening inflammation or tissue damage caused by those conditions.
Your doctor may be able to diagnose the cause of rectal bleeding based on your history and physical findings. If you have been taking iron supplements—even if a doctor did not prescribe them—be sure to include the dose and frequency in your history. In most cases your doctor will order blood tests to determine the duration and severity of rectal bleeding and schedule a colonoscopy to inspect the rectum and colon directly.
Treatment for rectal bleeding depends on its cause. If your doctor conclusively diagnoses it as constipation due to iron supplements, he will probably recommend that you stop taking the supplements or that you take a different type or dose. Rectal bleeding can cause you to become iron deficient. If the underlying cause of your rectal bleeding is untreatable, your doctor may recommend that you take intramuscular or intravenous iron injections because, unlike oral iron supplements, they do not cause gastrointestinal problems.
Consuming a diet that contains adequate iron may eliminate your need for iron supplements. Good sources of iron include lean cuts of red meat, poultry, fish, egg yolks and legumes. Combining these foods with vitamin C–rich fruits and vegetables such as citrus fruits, broccoli, tomatoes, strawberries, peppers and potatoes enhances your ability to absorb iron. If your doctor still recommends that you take iron supplements, carefully follow her instructions on the dose, timing and type of iron you should take.
Do not take iron supplements unless your doctor tells you to do so. In addition to rectal bleeding, other side effects such as upset stomach, abdominal pain, nausea and vomiting can occur with iron supplementation. Chronic use of unnecessary iron supplements can lead to a condition called iron overload. Iron overload is characterized by organ failure and arthritis related to iron deposition in the heart, liver, pancreas, brain or joints. If you take iron supplements, always inform your health care providers. Iron supplements can cause a false positive on some tests for gastrointestinal bleeding.
- Medline Plus: Gastrointestinal Bleeding
- "Harrison's Principles of Internal Medicine, 23rd Edition”; Anthony S. Fauci, M.D. et al.; 2008