BOSTON – Popeye’s prescription won’t restore iron levels in a child with frank anemia.
By the time iron-deficiency anemia has developed, no amount of spinach – or any other iron-rich food – can bring iron levels back up to normal, at least without the assistance of medical iron therapy.
"You can give a child three steaks a day and you won’t be able to get enough iron in to normalize the level," Dr. George Buchanan said at the annual meeting of the American Academy of Pediatrics. "Iron-rich foods can prevent iron deficiency, but they cannot treat it."
The reason lies in the body’s tightly controlled iron homeostasis. Just 10% of dietary iron is absorbed, and that amount varies widely because bioavailability differs among foods.
Breast milk, while relatively low in iron, has a very high bioavailability of 50%, said Dr. Buchanan, professor of pediatrics at the University of Texas Southwestern Medical Center, Dallas. Cow’s milk contains the same amount of iron – about 1 mg/L – but humans absorb very little of it.
So while cow’s milk is a perfect food for little bovines, it’s an imperfect food for little humans. "There’s not much iron in it, it’s poorly absorbed, and when the child’s stomach is full of cow’s milk, the appetite for other foods is not good. It’s not like we want to ban it – it’s a good source of vitamin D and calcium – but 24 ounces a day is all a toddler needs."
Overreliance on cow’s milk is only one possible contributor to childhood anemia, Dr. Buchanan said. Occult bleeding from the gastrointestinal tract, esophagus, lungs, or kidneys can be just enough to tip an infant, especially a preemie, into anemia. Nosebleeds and menorrhagia contribute to anemia in older children, as can sports activity. "Teens are in a stage of rapid growth and often poor diet, combined with an increase in physical activity," Dr. Buchanan said. Jogging or other vigorous activity can cause just enough minor intestinal trauma to leach away precious hemoglobin.
Genetic diseases also can underlie anemia. Pediatricians are familiar with thalassemia, but might not know about the recently described iron-refractory iron-deficiency anemia (IRIDA).
Children with a mutation in the TMPRSS6 gene produce too much hepcidin, a protein that regulates intracellular iron transport. Its normal function is to protect cells from taking up too much iron; an excess prevents iron from migrating into cells, keeping it in storage.
Proton pump inhibitors and H2 receptor antagonists can also interfere with iron absorption.
No matter what the cause, frank anemia is the last stage of iron depletion. The process starts when stored iron isn’t replaced, leading to iron-deficient erythropoeisis. Iron-deficiency anemia is the final stage of the process.
Various tests can identify each stage of the disorder, "But it may not be feasible or practical to do all of these," Dr. Buchanan said. The iron absorption test is the simplest way to quantify the stage of iron depletion, and to differentiate dietary deficiency from malabsorption syndromes.
"All of these factors can be screened for with this underutilized test," which consists of a single oral dose of 1 mg/kg iron. Serum iron is measured at baseline and 2 hours after the dosing. "The level in a normal child without iron deficiency will increase only slightly. In a child with a poor diet, it will be markedly increased. And in a child with malabsorption, the level won’t change at all."
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