• A shortage of certain vitamins in your diet
• An excessive loss of blood (from a stomach ulcer, for example)
• Chemotherapy

Red blood cells—why are they so important?

Red blood cells are important because they carry oxygen to all parts of your body. Oxygen is required for energy and to keep your body functioning properly. When the number of red blood cells falls below a certain number, oxygen is in short supply. Without enough oxygen in your body, you begin to feel tired and weak.

Common signs of anemia

• Mild fatigue to extreme exhaustion
• Weakness
• Dizziness
• Shortness of breath
• Inability to do normal activities

How chemotherapy causes anemia

The medicines that are used to treat your cancer work by attacking and destroying the cancer cells. These cancer cells are different from the other cells in your body in that they multiply and grow very quickly. Chemotherapy targets all quick-growing cells.

However, there are normal cells in your body that also grow quickly, like the cells in your scalp (the hair follicles) and the cells in your bones (bone marrow cells or blood cells). Unfortunately, as chemotherapy works to destroy the cancer cells in your body, it also can affect other cells, namely, red blood cells. And that's where anemia comes in.

Chemotherapy attacks red blood cells and actually interrupts the process of cell development that takes place deep inside your bones.

When this happens, the number of red blood cells circulating throughout your body drops lower and lower—the amount of oxygen available to your lungs and other organs is less and less—and you begin to feel more tired, more fatigued. Eventually, if left untreated, the number of red blood cells remains low and results in anemia.