Teenagers who suffered iron deficiency as infants are likely to score lower on cognitive and motor tests, even if that iron deficiency was identified and treated in infancy, a new study shows.
The study followed children who received treatment for their iron deficiency but they still showed ill effects up to adulthood. The findings emphasises the importance of preventing infant iron deficiency in the first place, say the researchers.
Iron deficiency with anaemia affects about 25 per cent of infants worldwide and twice as many have iron deficiency without anaemia. Many poor and minority children in the developed countries are also affected.
Researchers at the University of Michigan in the US gathered data on Costa Rican children who were diagnosed with severe, chronic iron deficiency when they were 12-23 months old and were treated with iron supplements.
The team then examined 191 children in working- to middle-class families at five years, 11-14 years and again at 15-17, and found the iron-deficient babies grew up to lag their peers in both motor and mental measures.
Children who had good iron status as babies showed better motor skills than those who had been iron deficient, said Betsy Lozoff, director of the Center for Human Growth and Development at the University of Michigan, presenting the findings at the Pediatric Academic Societies' annual meeting in San Francisco earlier this week.
That gap remained throughout childhood and adolescence. "There is no evidence of catch up," she said.
But even worse were the cognitive measures: children who had previously suffered iron deficiency not only lagged behind their peers, but the difference actually increased over time. They scored about six points lower on cognitive tests at age one to two years, and 11 points lower at age 15-18 years.
The gap was even more pronounced for children of families with low socioeconomic status, lower stimulation in the home or mothers lower in IQ.
For children with good iron status, family conditions did not seem to affect their cognitive test scores. For formerly iron deficient children, however, those in better family conditions started a little lower than peers and held there, while those in poorer family conditions started lower than their peers and then declined further.
"It looks like good iron status helps buffers a bad environment but chronic, severe iron deficiency, combined with poor family conditions, really hurts children's test performance," said Lozoff.
Since this study followed children through their adolescence, Lozoff's team wondered whether the same children accounted for the lower test scores at every age.
They looked at the good iron status group and broke their infant test scores into three levels: high, medium and low. Those children who scored well initially tended to score slightly worse later, and those who scored worse initially tended to see their scores increase later - described by statisticians as regression to the mean, or tending toward the average over time.
But for the iron deficient children, also split into high, medium and low infant test scores, there were decreases in test scores over time at all levels. Lozoff said this points out that regardless of where the children started on the test score spectrum, they still showed a decline as they got older.
Lozoff emphasised that these results are not a function of extreme poverty or general malnutrition. "This is a uniformly literate population," she said.
During development, iron performs a variety of important roles. Iron is required to build myelin, which covers nerves and helps them share signals more efficiently, for example. Iron is also needed for brain chemicals, such as the neurotransmitter dopamine, which sends signals within the brain. Iron deficiency also differentially affects the hippocampus, which is involved in certain types of memory and other important processes.
Babies typically get their iron from the mother during pregnancy and from mother's milk, but their rapid growth demands even more iron after the first four to six months. Other foods infants often eat, such as soft cereals, cow's milk and fruits, are poor sources of iron. In the United States, fortifying baby formula and cereals with iron has helped a great deal, but these have not been adopted internationally, and iron deficiency remains more common elsewhere.
The American Academy of Pediatrics has information on iron intake for infants.