Iron deficiency anemia is caused by low iron levels in the body, which may be the result of bleeding in the digestive tract. Common causes of digestive tract bleeding are:

• Regular use of nonsteroidal anti-inflammatory drugs (NSAIDs) such as aspirin and ibuprofen. These medicines may deplete iron stores by irritating the stomach lining, causing it to bleed. Iron is depleted by blood loss.
• Inflammatory bowel disease.
• Colon polyps or colorectal cancer, especially in older adults. It is important to identify and treat these as early as possible, because they may be life-threatening.
• Frequently occurring hemorrhoids. People with hemorrhoids often do not seek treatment right away, resulting in chronic bleeding.
• Hookworm and other parasites. These parasites feed upon blood from the intestinal wall. Significant blood loss can result if they are left untreated.
• Long-distance running (runner's anemia). People who regularly run long distances often have some type of bleeding in the digestive tract.¹