The results of this study showed that a home-based intervention in infants with IDA resulted in gains in cognitive and positive social-emotional scores that were similar to those observed in nonanemic infants regardless of intervention. Infants with IDA who were randomly assigned to the surveillance group showed smaller gains in cognitive performance and worsening positive social-emotional responsiveness. However, infants with IDA who received intervention did not catch up to non-anemic infants in social-emotional ratings; the similar rates of change indicate that the initial difference was maintained. Because infants were randomly assigned to groups, the benefits to infants with IDA seem to be attributable to the intervention program.
Comparisons of our findings with those from previous research are not possible, because no such intervention study has been published with respect to IDA. However, our findings are similar to those from studies of undernutrition (or zinc deficiency).14-–23,39 Such studies have shown that development improves when infants with generalized undernutrition or a specific micronutrient deficiency are offered early intervention in addition to health monitoring and nutritional rehabilitation.
The benefits that we observed corresponded to the nature of the intervention, which focused on the mother-infant relationship and aspects of maternal behavior thought to foster cognitive and social-emotional development.40
These are the areas in which infants with IDA who received intervention showed developmental improvements compared with those who received surveillance without intervention. Note that all infants were visited weekly to maintain comparability in the frequency of contact with study personnel. Thus, all infants could be considered to have received some kind of intervention. The impact of the early-intervention program may have been even greater compared with routine health care alone.
In contrast to previous investigators,1,3
we did not observe lower initial cognitive and motor scores in infants with IDA. In our study population, however, infants with IDA showed less positive social-emotional responsiveness and were observed to have delayed development, as assessed on the basis of more brain-based measures.26,29
This pattern of results suggests that in the first year of life global cognitive and motor scores are not as sensitive to IDA effects as are social-emotional or more brain-based measures. This interpretation is supported by our recent study of 9-month-old infants in an inner-city US population, in whom social-emotional measures showed more marked differences related to iron status than overall cognitive and motor scores.41–43
Positive social-emotional behavior was also the area most improved by iron supplementation in the preventive trial component of the Chile project.24
Together such results point to the following conclusions: positive social-emotional behavior may be fostered by iron supplementation as a preventive measure but is not fully corrected once IDA occurs, even with additional intervention. Social-emotional behavior may get worse without intervention, even when IDA is treated with iron.
Another possible reason why we did not observe lower initial cognitive and motor scores is that IDA was not present long enough to have an impact on global scores. No infant had IDA postnatally for >6 months, because IDA was identified and treated at 6 and 12 months. In previous studies, infants were older and probably had IDA longer.2–5
Even in the present study, however, infants with IDA who did not receive intervention showed lower cognitive scores as the year went on, despite iron therapy.
Our study could not be double-blind. Although infants were randomly assigned to surveillance and intervention groups and outcomes were measured by masked testers, mothers and families knew which group their infant was in. In regard to generalizability, it is unclear whether such an intervention program would be equally effective if IDA was more chronic or severe or families more or less advantaged than those in our sample. The labor-intensive nature of the intervention and our use of skilled professionals also limit broad application. Concerted efforts are underway to identify developmentally supportive interventions that are feasible and sustainable on a large scale.20,44
For instance, approaches involving less skilled personnel and homemade toys have shown good results in several contexts.15–18,21–23,39
The optimal age for intervention remains unclear, although there was no differential effect associated with infant age in our study. Processes by which early-intervention programs produce benefits are also not well understood and warrant additional research.