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Have you felt exhausted lately? Can you barely make it up the stairs without getting winded even though you're physically fit? If so, you might be lacking in iron -- especially if you're a woman.

Although many people don't think of iron as being a nutrient, you might be surprised to learn that low iron is the most common nutritional deficiency in the U.S. Almost 10% of women are iron deficient, according to figures from the Centers for Disease Control and Prevention.   

Let's look at why iron is so important to your body, what can happen if you're not getting enough of it, and when you need to take an iron supplement.

Why Do You Need Iron?

Iron is an essential mineral. "The major reason we need it is that it helps to transport oxygen throughout the body," says Paul Thomas, EdD, RD, a scientific consultant to the National Institutes of Health, Office of Dietary Supplements.

Iron is an important component of hemoglobin, the substance in red blood cells that carries oxygen from your lungs to transport it throughout your body. Hemoglobin represents about two-thirds of the body’s iron. If you don't have enough iron, your body can't make enough healthy oxygen-carrying red blood cells. A lack of red blood cells is called iron deficiency anemia.

Without healthy red blood cells, your body can't get enough oxygen. "If you're not getting sufficient oxygen in the body, you're going to become fatigued," Thomas says. That exhaustion can affect everything from your brain function to your immune system's ability to fight off infections. If you're pregnant, severe iron deficiency may increase your baby's risk of being born too early, or smaller than normal.  

Iron has other important functions, too. "Iron is also necessary to maintain healthy cells, skin, hair, and nails," says Elaine Chottiner, MD, clinical assistant professor and director of General Hematology Clinics at the University of Michigan Medical Center said in an email interview.

How Much Iron Do You Need?

How much iron you need each day depends on your age, gender, and overall health.  

Infants and toddlers need more iron than adults, in general, because their bodies are growing so quickly. In childhood, boys and girls need the same amount of iron -- 10 milligrams daily from ages 4 to 8, and 8 mg daily from ages 9 to 13.  

Starting at adolescence, a woman's daily iron needs increase. Women need more iron because they lose blood each month during their period. That's why women from ages 19 to 50 need to get 18 mg of iron each day, while men the same age can get away with just 8 mg.  

After menopause, a woman's iron needs drop as her menstrual cycle ends. After a woman begins menopause, both men and women need the same amount of iron -- 8 mg each day.

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