Context: Problems can occur with red blood cells, white blood cells, platelets, and other parts of the blood. Many blood disorders are genetic, meaning they are inherited from a parent. Some blood diseases are caused by not getting enough of a certain nutrient, while others are cancers of the blood. Anemia is a disease that occurs when there is not enough hemoglobin in the blood to carry oxygen to body cells. Hemoglobin is the blood protein that normally carries oxygen from the lungs to the tissues. Anemia leads to a lack of oxygen in organs. Anemia is usually caused by one of the following: A loss of blood from a bleeding wound or a slow leak of blood. The destruction of red blood cells. A lack of red blood cell production. Anemia may not have any symptoms. Some people with anemia feel weak or tired in general or during exercise. They also may have poor concentration. People with more severe anemia often get short of breath during times of activity. Iron-deficiency anemia is the most common type of anemia. It occurs when the body does not receive enough iron. Since there is not enough iron, hemoglobin, which needs iron to bind oxygen, cannot function properly. In the United States, 20% of all women of childbearing age have iron-deficiency anemia, compared with only 2% of adult men. The most common cause of iron-deficiency anemia in young women is blood lost during menstruation. Iron deficiency anemia can be avoided by getting the recommended amount of iron in ones diet. Anemia is often treated or prevented by taking iron supplements. Boys and girls between the ages of 9 and 13 should get 9 mg of iron every day. Girls between the ages of 14 and 18 should get 15 mg of iron every day. Boys between the ages of 14 and 18 should get 11 mg of iron every day. Pregnant women need the most iron27 mg daily. Good sources of iron include shellfish, such as clams and oysters. Red meats, such as beef, are also a good source of iron. Non-animal sources of iron include seeds, nuts, and legumes. Breakfast cereals often have iron added to them in a process called fortification. Some good sources of iron are listed below ( Table 1.1). Eating vitamin C along with iron-containing food increases the amount of iron that the body can absorb. Food Canned clams, drained, 3 oz. Fortified dry cereals, about 1 oz. Roasted pumpkin and squash seeds, 1 oz. Cooked lentils, 12 cup Cooked fresh spinach, 21 cup Cooked ground beef, 3 oz. Cooked sirloin beef, 3 oz. Milligrams (mg) of Iron 23.8 1.8 to 21.1 4.2 3.3 3.2 2.2 2.0 Sickle-cell anemia is a blood disease that is caused by an abnormally shaped hemoglobin protein in red blood cells. Many of the red blood cells of a person with sickle-cell anemia are long and curved (sickle-shaped) ( Figure 1.1). The long, sickle shape of the cells can cause them to get stuck in narrow blood vessels. This clotting means that oxygen cannot reach the cells. People with sickle-cell anemia are most often well but can occasionally have painful attacks. The disease is not curable, but it can be treated with medicines. The red blood cells of a person with sickle-cell anemia (left) are long and pointed, rather than straight, like normal cells (right). The abnormal cells cannot carry oxygen properly and can get stuck in capillaries. Blood cancers affect the production and function of your blood cells. Most of these cancers start in your bone marrow where blood is produced. In most blood cancers, the normal production of blood cells is replaced by uncontrolled growth of an abnormal type of blood cell. These abnormal blood cells are cancerous cells, and prevent your blood from performing many of its functions, like fighting off infections or preventing serious bleeding. Leukemia is a cancer of the blood or bone marrow. It is characterized by an abnormal production of blood cells, usually white blood cells. Lymphoma is a cancer of a type of white blood cell called 
 Question: which food is the best source of iron?
Output: shellfish