More than a third of American women between the ages of 12 and 21 have an iron deficiency, according to new research published in the Journal of the American Medical Association.

The research published online last week found nearly 39 percent of American girls and women aged 12-21 were affected by iron deficiency, and 6 percent were iron-deficient anemic. 

The body uses the mineral iron to make the essential protein hemoglobins and myoglobin, which help the body get oxygen. Age, sex and diet are among the factors in how much iron is needed.

The National Institutes of Health noted teenage girls, women with heavy periods and pregnant women are “more likely than others to have trouble getting enough iron.”

While iron deficiency, or low iron in the body, often presents no symptoms, the more severe iron-deficiency anemia impacts red blood cells and hemoglobin levels and can cause tiredness, shortness of breath, heart palpitations and other symptoms. 

Left untreated, iron-deficiency anemia can make the body more prone to infection and cause complications in pregnancy. 

Using data from 2003-2010 and 2015–March 2020, the new study — from researchers at University of Michigan Medical School, Brigham and Women’s Hospital and elsewhere — looked for insights related to ferritin, a blood protein that contains iron, in 3,490 individuals from the National Health and Nutrition Examination Survey.

Though menstruation was found to be a risk factor for iron deficiency and iron-deficiency anemia in the young women, more than a quarter of girls who had not yet hit the onset of their periods also had iron deficiency. 

The study concludes that risk factors for iron deficiency, like low iron intake and extensive menstrual blood loss, “are not clearly defined” and that “current screening guidance may miss many individuals with iron deficiency.”