context: Every organ and tissue in your body needs oxygen to work. Red blood cells are the transport system that carries oxygen from your lungs to the rest of your body. When you have anemia, your body doesn't have enough of these blood cells. You get iron deficiency anemia when your body is low in iron. You need iron to make hemoglobin -- a protein that helps your red blood cells carry oxygen. Without enough oxygen in your blood, and you may feel tired, weak, and short of breath. Your doctor will find out why your iron is low. Usually, you can treat iron deficiency anemia with supplements. Once your iron levels increase, you should start to feel better. It can happen if you don't eat enough foods containing iron, your body can't properly absorb iron, you lose iron through your blood, or you're pregnant. Your diet is low in iron. How much iron you need depends on your age and gender. Men need at least 8 milligrams (mg) daily. Women ages 50 and younger need more -- 18 mg. Your body can't absorb iron. Iron from the foods you eat is absorbed in your small intestine. Conditions like celiac disease, ulcerative colitis, or Crohn's disease can make it harder for your intestines to absorb iron. Surgery such as gastric bypass that removes part of your intestines, and medicines used to lower stomach acid can also affect your body's ability to absorb iron. Blood loss. Some conditions can make you bleed inside your body, including: Peptic ulcer Hernia Uterine fibroids Colon polyps Women with heavy periods can become low in iron. Also, injuries and frequent blood donations can cause it. Pregnancy. When you're expecting, you need extra iron to nourish your growing baby. If you don't get enough iron from your diet or supplements, you can become deficient. Mild iron deficiency anemia often isn't noticeable. When it gets more severe, you may have these symptoms: Tiredness or weakness Pale or yellow skin Shortness of breath Dizziness Headaches Fast heartbeat Chest pain Cold feet and hands Brittle, cracked nails and hair loss Pica (cravings for things that aren't food, like dirt, starch, clay, or ice) Sore and swollen tongue Restless legs syndrome (an urge to move your legs while you're in bed) Because these can also be symptoms of other conditions, see your doctor to get a diagnosis. Your doctor will do one or more of these blood tests to find out if you have iron deficiency anemia. Complete blood count ( CBC). This test checks to see how many red blood cells you have. Peripheral blood smear. This test looks at the size and shape of your red blood cells. In iron deficiency anemia, red blood cells are smaller than usual. Hematocrit. This test shows how much of your blood is made up of red cells. Hemoglobin. This test shows the amount of this protein in your blood. If you have anemia, your hemoglobin will be low. Serum iron. This test shows how much iron is in your blood. Ferritin. This test shows how much iron is stored in your body by measuring this protein. Transferrin and total iron-binding capacity ( TIBC). These tests show how much of a protein called transferrin is free to carry iron through your body. Reticulocyte count. This test shows how many reticulocytes (immature red blood cells) you have in your blood. If you have iron deficiency anemia, your reticulocyte count is usually low because you're not making many new red blood cells. If blood tests show you have iron deficiency anemia, you might need other tests like these to see what's causing it. Endoscopy. Your doctor uses a tube with a camera on one end to look inside your esophagus or colon. Endoscopy can find bleeding in your GI tract from ulcers, polyps, or other growths. Pelvic ultrasound or uterine biopsy. If you bleed a lot during your monthly periods, this test can find the cause. Fecal occult blood test. This test looks for tiny amounts blood in your poop to check for cancer and other causes of bleeding in your intestines. You can treat iron deficiency anemia by taking iron supplements. Most people take 150 to 200 milligrams (mg) each day, but your doctor will recommend a dose based on your iron levels. Take vitamin C, too. It helps your body absorb the iron. You might need to take iron supplements for a few months or more to get your levels back up to normal. If your intestines don't absorb iron well, you can take iron straight into your bloodstream through an intravenous tube ( IV). But be warned: Iron supplements can cause constipation, nausea, vomiting, diarrhea, heartburn, and dark poop. Your symptoms should start to go away after about a week. Your doctor will check your blood to see if your anemia has improved. You can also get more iron in your diet by eating more of these foods: Beef, pork, liver, chicken, turkey, duck, and shellfish Leafy greens such as broccoli, kale, turnip greens, and collard greens Peas, lima beans, black-eyed peas, and pinto beans Iron-enriched cereals and other grains Dried fruits, such as prunes and raisins If supplements don't help with your symptoms or your anemia is severe, you might need a transfusion of red blood cells. Or, if you have an ulcer, tumor, or other growth, it may need to be treated with medicines or surgery.