From the Research
Iron supplements should be avoided for at least 7 days before a colonoscopy to ensure optimal visualization of the colon lining during the procedure. This is because iron can cause dark, sticky stools that adhere to the colon wall, potentially obscuring important findings such as polyps or small lesions 1, 2, 3, 4, 5. The dark stool occurs because not all iron is absorbed by the body, and the unabsorbed portion passes through the digestive tract, creating a black or dark green discoloration.
Key Considerations
- Iron supplements, including ferrous sulfate, ferrous gluconate, and multivitamins containing iron, all produce this effect.
- If you're taking iron for medical reasons, consult with your doctor before stopping it, as they may need to adjust your preparation instructions or reschedule your procedure if iron supplementation cannot be temporarily discontinued.
- You can typically resume taking iron supplements the day after your colonoscopy is completed.
Evidence Summary
The provided studies do not directly address the question of why iron supplements should be avoided before a colonoscopy. However, the most recent and highest quality study 5 suggests that long-term changes in dietary iron can affect gut microbiota signatures and exacerbate acute colitis. While this study does not directly relate to colonoscopy preparation, it highlights the potential impact of iron on the gastrointestinal tract.
Clinical Implications
In clinical practice, it is essential to prioritize the visualization of the colon lining during a colonoscopy to ensure accurate diagnosis and treatment. Avoiding iron supplements for at least 7 days before the procedure is a simple and effective way to minimize the risk of dark, sticky stools and ensure optimal visualization. If a patient is taking iron for medical reasons, it is crucial to consult with their doctor to determine the best course of action.