Colorectal cancer is the third most common cancer worldwide. Patients with this disease often suffer from anemia, a lack of red blood cells (RBCs). RBCs are required to transport oxygen around the body. Anemia is associated with symptoms such as fatigue, shortness of breath, palpitations, dizziness and headaches. Besides these unpleasant symptoms, it can also contribute to a poorer prognosis for bowel cancer. Anemia is caused by a lack of iron, which is essential for the formation and function of RBCs. This deficiency can be either absolute or functional. An absolute iron deficiency is caused by blood loss. This is common in bowel cancer and can appear in different ways. You may not notice anything, there may be bright red blood in the stools, or there may be black stools. Absolute iron deficiency can also occur as part of cancer treatment if a lot of blood is lost during surgery. In a functional deficiency, there is enough iron in the body but it cannot get to its destination, so it is unable to fulfil its function. Colorectal cancer causes inflammation in the body and activates the immune system, which increases the hormone hepcidin. This hormone has a regulatory role in iron hemostasis and makes it unavailable for the production of RBCs, leading to the functional deficiency. Administration of iron (orally or intravenously) can be effective in treating anemia. However, it is important to note that iron also plays a complex role in the development of colon cancer and in the immune system. For these reasons, it is important to understand the effects of iron supplementation on the immune system and anemia in patients who have undergone surgery for their cancer. To achieve this, a systematic review was conducted. A key finding was the importance of using the pre- and postoperative period to optimise the patient's condition. In most trials, iron administration led to an increase in hemoglobin, an essential protein in RBCs. However, the need for blood transfusions was often undiminished, somewhat masking the beneficial effect on hemoglobin. There were no clear, consistent improvements in oncological outcomes, survival, quality of life or length of hospital stay. However, postoperative complication rates were slightly lower in patients who received iron supplementation. Iron was also shown to be a safe therapy. In conclusion, more large and long-term trials are needed to determine the most effective treatment, although individual factors will always play a role in the choice of treatment.