What Happens When Your Iron Is Low?

  • Medical Reviewer: Dany Paul Baby, MD
Medically Reviewed on 6/1/2022

Iron's role in the body

Low iron is the most common nutritional deficiency in the world. If you are anemic, you do not have enough healthy red blood cells.
Low iron is the most common nutritional deficiency in the world. If you are anemic, you do not have enough healthy red blood cells.

Being low on iron is one cause of anemia. If you are anemic, you do not have enough healthy red blood cells. You also may be low on hemoglobin, a protein inside red blood cells. Hemoglobin carries oxygen to all the tissues of the body. Without enough red blood cells and enough hemoglobin, you may feel weak, dizzy, and tired from lack of oxygen.

Low iron is the most common nutritional deficiency in the world. Around one-quarter of the world's population has anemia. Low iron causes about half of the cases of anemia. 

When you eat food that contains iron, the small intestine absorbs part of the iron and the liver stores some. When the body needs more iron, the liver releases some of its reserves. The released iron travels to the bone marrow and helps to make red blood cells. Red blood cells have a life span of about four months. When they stop working, they travel to the spleen. There the body reabsorbs them and reuses some of the iron. The body needs fresh stores of iron, too.  

Iron deficiency anemia develops slowly. In its earliest stage, the amount of stored iron in the body drops. Next, the bone marrow produces fewer red blood cells. In the last stage, the body's stores of iron are gone.  When this happens, your body will make fewer red blood cells that are also smaller in size. 

What causes low iron? 

There are three basic reasons you might have low iron:

  • You aren't taking in enough iron
  • You aren't absorbing the iron you have taken in
  • You are losing iron in the form of red blood cells

Also, women may become iron deficient while pregnant because their need for iron increases. Women need around one-third more iron during pregnancy.

Getting iron from foods

The amount of iron you need depends upon your age and gender. The recommended daily allowance ranges from 7 to 27 milligrams per day. Vegetarians need to take in more iron because the body doesn't absorb the iron in plants as well as the iron in meat. Eating foods that contain vitamin C along with iron-rich foods improves the absorption of iron.  

In the United States, many grain products have iron added to them. One serving of fortified breakfast cereal may give you enough iron for the whole day. If you prefer to get your iron from natural sources, you have plenty of choices. Lean meat, seafood, nuts, beans, and vegetables are good sources of iron. Here are some sample amounts: 

  • 3 ounces of beef liver: 5 milligrams
  • 3 ounces of oysters: 8 milligrams
  • 1 cup of white beans: 8 milligrams
  • 1 medium potato with the skin: 2 milligrams
  • 1 ounce of cashews: 2 milligrams

Problems absorbing iron

A small percentage of people develop iron deficiency because they have trouble absorbing iron. The most common cause is a gastrointestinal disorder such as Crohn's disease or celiac disease. Those who have had gastric bypass or similar surgeries may also be at risk. 

Low iron due to blood loss

If you are losing blood, you are losing red blood cells and may develop anemia. You could be losing blood for several reasons.

Heavy menstrual periods. Experts believe that menstrual bleeding causes more than one-third of low iron cases in women. Around one-tenth of women have heavy menstrual bleeding, called menorrhagia

Blood lost in the stool. You may pass blood in the stool without noticing it. This type of blood loss can be caused by:

Less often, you can become anemic because of nosebleeds, hemorrhoids, or tumors in the kidney or bladder that cause you to pass blood in the urine.

People who donate blood are also at risk for low iron. From 25% to 35% of regular donors become anemic. Those who take an iron supplement recover their iron stores faster after a donation.

Symptoms of low iron

If you have iron-deficiency anemia, you may feel tired, dizzy, weak, and short of breath. Your skin may be pale, and you may have restless leg syndrome, which is an urge to move your legs when you are trying to rest. 

Doctors rarely diagnose low iron by an office visit alone. Symptoms like fatigue can have many causes. In one study, 52 people complained of fatigue, and only one was anemic. Pale skin is even less reliable as a diagnostic tool. Doctors can order blood tests that can accurately diagnose anemia. If you have anemia, your doctor will order further tests to find out why your iron is low.

Treatment for iron deficiency

It's important to be treated for anemia because it can be dangerous. It can cause heart problems and frequent infections. Children with anemia may not develop as they should. Pregnant women who are anemic may have problems with their pregnancy

If you are anemic, your doctor will probably give you iron supplements. In some cases, your doctor may give you iron through a vein. Intravenous iron has some advantages but can trigger allergic reactions. If you have severe anemia with shortness of breath, your doctor may order blood transfusions. These will replace the blood lost but will not correct the underlying cause. 

If you have low iron, you will need to take iron for some time so that your body can build up its stores. In addition, your doctor should look for the cause of your anemia and work to correct it. 


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Can you get too much iron?

It's hard to get too much iron from your diet, but you can get too much from supplements. Too much iron can cause organ damage. Most of the time, you should get no more than 45 milligrams of iron a day. 

A few people have a genetic condition called hemochromatosis, which causes a toxic buildup of iron in the body. They should avoid iron supplements and follow a doctor's advice closely.

Low iron in children

Infants need a lot of iron because they grow rapidly. Full-term babies usually have enough iron stored in their bodies for the first few months of life. After that, they will need iron-rich foods or formula that has been fortified with iron. Your baby's doctor will screen your child for iron deficiency and recommend supplements when needed. Babies who are born early or who have low birth weight may need iron supplements soon after birth. 

Medically Reviewed on 6/1/2022

American Family Physician: "Iron Deficiency Anemia."

American Society of Hematology: "Iron-Deficiency Anemia."

Merck Manual Consumer Version: "Anemia Due to Excessive Bleeding."

Merck Manual Professional Version: "Iron Deficiency Anemia."

National Institutes of Health Office of Dietary Supplements: "Iron."

Office on Women's Health: "Iron-deficiency anemia."

Warner, M., Kamran, M. StatPearls, “Iron Deficiency Anemia,” StatPearls Publishing, 2021.

World Health Organization: "Anaemia."