A clinical trial by investigators at the Johns Hopkins Children's Center found that when teenage girls who are not anemic but have iron deficiency took iron supplements, they performed significantly better on verbal learning tests than girls who took a placebo. This finding could help the estimated 25 percent of adolescent females in the United States who are iron deficient. The study appears in the Oct. 12 issue of Lancet.
"Teenage girls should be regularly tested for iron deficiency because rapid growth and the onset of menstruation during puberty increase the body's need for iron," says Ann Bruner, M.D., of the Hopkins division of general pediatrics and lead author of the study. "Girls who exercise and those who eat foods lacking or low in iron have an increased risk of developing iron deficiency," she adds. While severe iron deficiency can lead to anemia (not enough red blood cells), this study was designed to look at the effects of iron deficiency in the absence of anemia. Before the 1993-94 school year, investigators contacted more than 2,000 female students aged 14-18 years enrolled at two public and two private Catholic high schools in Baltimore: Paul Laurence Dunbar High School, Baltimore City College, The Catholic High School, and The Institute of Notre Dame. Working closely with teachers, administrators and parents, investigators recruited 716 girls who volunteered to have their blood tested for iron deficiency. Overall, 112 girls (15.6 percent) were found to have it.
Investigators then enrolled 81 of those girls in a study of the effects on attention, memory and learning of 260 mg. of elemental iron supplementation per day for eight weeks. The participants were randomly divided into two groups; half the teens took an iron supplement while the other half took a placebo. Before beginning the study, the girls took four cognitive tests to measure their baseline attention, memory and learning.
After eight weeks, Bruner and colleagues repeated the cognitive tests. They found no difference between the two groups on the attention tests. However, girls who took iron supplements did significantly better on verbal learning and memory tests than the girls who took the placebo. Bruner says this suggests that even in the absence of anemia, iron deficiency may impair learning in adolescent females. Possible explanations for this effect come from animal research in which iron deficiency changes brain iron levels and alters neurotransmitter production, function, and breakdown.
Previous research has shown that iron deficiency anemia impairs performance on developmental tests in infants and toddlers. After treatment with iron supplements, many infants showed some developmental improvement.
Bruner says that more studies need to be done to determine if iron deficiency can affect students' general academic achievement. Other questions to be answered include how best to test for iron deficiency and which adolescents have the highest risk of developing it.
Co-authors on the study are Alain Joffe, M.D., M.P.H.; Anne Duggan, Sc.D.; Jason Brandt, Ph.D.; and James Casella, M.D. Partial funding for the study was provided by SmithKline Beecham.
The Johns Hopkins Children's Center is the children's hospital of The Johns Hopkins Medical Institutions. Maryland's only comprehensive acute-care hospital for children, the Center with its 177-bed hospital and more than 40 divisions and services, treats some 8,000 inpatients annually, with more than 90,000 outpatient visits.