The risk factors and causes of anemia differ for each type of anemia. However, in general, anemia is caused one or more of these three factors:

• Loss of blood
  
• Low red blood cell production
  
• High red blood cell destruction

There are several causes for each of these factors, some of which are genetic and some acquired. For example, heavy blood loss can occur after trauma, conditions that cause internal bleeding or heavy menstrual cycles. Some other causes of anemia include:

• Malnutrition. A deficiency in certain nutrients, particularly iron, folate or vitamin B12, can result in anemia. Deficiency in these can affect how many red blood cells are produced. It can also reduce the life expectancy of red blood cells. In most cases, correcting the deficiency can resolve the anemia, although some people may require supplements for life.
  
  
• Chronic disease. Some chronic diseases, such as AIDS, cancer or kidney disease, can affect the body's ability to produce red blood cells.
  
  
• Cancer treatment. Treatment methods for cancer, including radiation therapy and certain medications, may result in anemia. For example, chemotherapy drugs target rapidly producing cells, including those in the bone marrow that are responsible for making new blood cells. Additionally, radiation therapy may completely destroy bone marrow. These treatments affect the amount of red blood cells that the body can produce.
  
  
• Pregnancy. During pregnancy, the fetus requires blood cells to grow and develop. In some women, the body cannot adjust easily to this increased demand, resulting in anemia.
  
  
• Hereditary disease. Many forms of anemia are caused by disorders that are passed down from generation to generation. For example, sickle cell anemia and thalassemia are inherited conditions that destroy red blood cells quicker than the body can replace them. Additionally, some patients may inherit certain immune disorders that attack red blood cells.

Women are at a higher risk of developing anemia than men because of the potential for blood loss during the menstrual cycle and increased need for blood cells during pregnancy. Older adults, especially those who live alone, are also at risk of developing anemia because of their tendency to skip meals and experience malnutrition.