Colon cancer can cause low hemoglobin, a well-recognized clinical finding. Hemoglobin is the protein in red blood cells that transports oxygen throughout the body. A low hemoglobin level signals anemia, meaning the body lacks enough red blood cells or hemoglobin to effectively carry oxygen. Colon cancer is frequently associated with iron-deficiency anemia. This occurs because the growing tumor often leads to a slow, chronic loss of blood, which depletes the iron supply necessary for producing new hemoglobin.
The Direct Cause: Chronic Blood Loss
The primary mechanism linking colon cancer to low hemoglobin is internal bleeding from the tumor surface within the digestive tract. As a cancerous growth develops, its surface becomes fragile and ulcerated, causing it to bleed. This blood loss is often not visible to the naked eye, a phenomenon called occult bleeding, and happens slowly over months or years.
Because the bleeding is gradual and persistent, the body loses small amounts of blood, along with the iron contained in the red blood cells. The body cannot absorb enough iron from diet alone to keep pace with this continuous loss. Iron is necessary for the bone marrow to manufacture new hemoglobin and red blood cells. This results in a progressive depletion of the body’s stored iron, leading directly to iron-deficiency anemia.
The location of the tumor influences the severity of blood loss and resulting anemia. Tumors on the right side of the colon, further from the rectum, can bleed for a longer time before the blood is noticeable in the stool. Right-sided cancers are often diagnosed specifically because of the unexplained iron-deficiency anemia they cause. The presence of the tumor also triggers chronic inflammation. This inflammation interferes with how the body uses available iron, further suppressing red blood cell production and compounding the anemia.
Impact of Low Hemoglobin on the Body
Chronic, low-grade blood loss impairs the delivery of oxygen to muscles and organs. Hemoglobin’s function is to bind to oxygen and release it where it is needed. When hemoglobin levels drop, the body’s tissues become oxygen-deprived, leading to noticeable physical symptoms.
The most common symptom is persistent fatigue and weakness, occurring because muscles lack the oxygen needed for energy production. People with anemia may also experience shortness of breath, especially during physical activity, as the heart and lungs compensate for the reduced oxygen-carrying capacity. Other signs include a rapid heartbeat and pale skin (pallor), caused by the reduced number of circulating red blood cells. These symptoms develop slowly, often leading people to attribute them to aging or being overworked.
Next Steps: Screening and Diagnosis
The discovery of low hemoglobin, especially iron-deficiency anemia in an adult, serves as a strong signal that requires a thorough medical investigation. If the cause is not immediately apparent (such as heavy menstrual bleeding), a physician will focus on identifying a source of internal blood loss. The first step is typically a Complete Blood Count (CBC), which measures hemoglobin levels and checks the size and color of red blood cells to confirm the type of anemia.
Further blood tests, such as a ferritin level, determine the body’s iron stores and confirm iron deficiency. Once confirmed, the diagnostic pathway often includes procedures to inspect the gastrointestinal tract for the source of bleeding. The most definitive procedure for evaluating the lower digestive tract is a colonoscopy, which uses a flexible scope with a camera to examine the entire colon. This allows the doctor to visually detect polyps or tumors responsible for the chronic blood loss. A prompt consultation with a healthcare provider is advisable to ensure underlying conditions, including colon cancer, are addressed early.