Anemia is a condition characterized by a decrease in the amount of hemoglobin and erythrocytes in the blood. The causes of anemia include decreased production of red blood cells in the bone marrow, reduction or breakdown of erythrocytes, excessive blood loss, decreased iron, pregnancy, menstruation, and inability to absorb iron. Signs of anemia consist of rapid fatigue, weakness, nervousness, dizziness, rapid heartbeat, pale skin, yellowing of the eyes, and bleeding from various parts of the body.