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How Long Before Iron Supplements Take Effect?

author image Valerie Webber
Valerie Webber started out as a technical writer in 1994 and transitioned into journalism in 2004. Her work has appeared in “The Gainesville Times,” “The Fauquier Times-Democrat,” “Merial Selections” and “SIDEROADS” magazine. Webber is also certified by the American Council on Exercise as a group fitness instructor.
How Long Before Iron Supplements Take Effect?
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Iron supplements, usually given in the form of ferrous sulfate, will start to take effect within the first week. However, the length of time it takes for your body to completely replenish your depleted iron stores will depend on how severe your anemia was to begin with, how long you've been anemic, how well your body is able to absorb the iron in the supplements and how good you are at remembering to take them.

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When you are anemic, your body is not making enough hemoglobin to carry oxygen to all of the cells of your body. Hemoglobin is a protein that carries oxygen in your red blood cells. Your bone marrow produces red blood cells using iron and vitamin B-12. According to the National Anemia Action Council, or NAAC, the most common cause of anemia is iron deficiency. Although most people in the U.S. get enough iron in their diets, some people have difficulty absorbing the mineral and others are losing blood faster than their bodies can replace the red blood cells.


Iron and B-12 are raw materials that your body needs to make new red blood cells. If your doctor has determined that you are anemic, she will probably do a blood test to be sure that it is iron deficiency and not another issue that is causing the problem. Most likely, she will prescribe iron supplements and give you specific instructions about when to take the pills. Once the supplements start to get into your system, your bone marrow will kick into action, turning out new cells. NAAC says it will take about a week for these new cells to begin circulating and about two to three weeks before your hemoglobin levels start to rise.


Your doctor will continue to test your blood while you are recovering from anemia. She might look at the amount of hemoglobin in your blood and the shape and color of your red blood cells in a microscope. According to the Three Rivers Endoscopy center in Pennsylvania’s website, anemia usually goes away within eight weeks of supplementation, but you may need to keep taking the supplements for six months or more so that your body can rebuild its reserves of iron to prevent you from having another bout of anemia.


Even though you may be taking large amounts of iron every day, your body will not be able to absorb all of that iron. Taking antacids or drinking milk with your pills can decrease the amount of iron you actually absorb. Drinking orange juice or other foods rich in vitamin C can help increase absorption. It's best to take the supplements on an empty stomach, but this might make you queasy. If you choose to take your supplements with food, NAAC says the amount of iron you absorb will decrease by about 40 to 60 percent, which means you will have to take the supplements for a longer period of time. If you frequently miss doses or stop taking the supplements, you will obviously have slower results.

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