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Early supplementary feeding, child development, and health policy
Ernesto Pollitt and Se-Young Oh
The possibility of bias resulting from a selective review of studies (the "file-drawer problem") was also considered in the analysis. We assumed that the results might have resulted from a failure of investigators to report studies showing a lack of effects, or a failure of journals to publish such findings [20]. The magnitude of such a bias was estimated by calculating the number of unpublished, not statistically significant studies that would be necessary to bring the overall probability value to greater than .05. Twenty-six null-result studies would be necessary to dilute the finding for the motor test at 8-15 months, 2 for the mental test at 18-24 months, and 16 for the motor test at 18-24 months.
The results of the meta-analysis agree in part with the hypothesis that drove the analysis. Among nutritionally at-risk populations, protein and calorie supplementation’s during pregnancy and during the first two years of postnatal life provide salutary effects on the motor development of children up to 24 months of age. On the other hand, there is no evidence that early supplementary feeding affects the mental development of children up to the age of 15 months. It does have an effect on mental development among children 18-24 months old.
The scientific merit of the meta-analysis is evident in the assessment of the effects on the mental development scores at 18-24 months. Although only one of the three studies found statistically significant differences between the supplemented and non-supplemented groups, all three found arithmetic differences between the groups in the direction of the proposed hypothesis. This trend became statistically meaningful by pooling the studies, substantiating the inference of a treatment effect on mental development among children 18-24 months old. We therefore conclude that providing high energy and protein supplementary foods to nutritionally at-risk infants and children up to 24 months of age prevents, in part, developmental delays.
The effects derived from prenatal supplementation are likely to result from the transport of nutrients from the mother to the foetus. This concurs with the finding that protein and calorie supplementation during pregnancy among nutritionally at-risk women results in increased birth weight of the offspring [4]. The pathways for the effect of postnatal supplementation are less clear. In reference to the mother, the supplementary food is expected to result in changes in the composition and volume of breast milk. However, data that are available from other studies on this issue show that supplementary feeding to the mother does not affect volume; only suggestive evidence exists that caloric supplementation affects milk composition [21]. An alternative explanation is that nutritional supplements to the mother during pregnancy and lactation have the potential of improving health conditions that will foster her investment in the unborn or born child [4, 22].
The one study that showed no effects on performance on the development scale was carried out in New York [4]. This study, in fact, is also the only one that failed to find an effect on birth weight. Reviewers of the experiment pointed out that the women who received the supplement were not nutritionally at risk, and therefore the absence of benefits on development is not surprising [23]. These findings, when compared with those from the other interventions, suggest that the benefits of early supplementary feeding on development are restricted to populations that are nutritionally at risk.
The benefits observed in performance on the mental development scales in the older group of subjects (15-24 months old) should not be interpreted to mean that the nutrition intervention prevents deficits in later intelligence.
The presence of developmental effects of supplements in the field intervention studies does not guarantee that such effects will be also observed in large-scale food assistance programmes, even if the programmes use supplements and are targeted to populations similar to those of the successful field studies. Tightly controlled experiments are not the same as large-scale programmes, whose effectiveness depends on large bureaucracies and administrative infrastructures that are not very efficient. This is particularly the case in developing countries because of budgetary limitations.
One potential adverse effect of supplementary feeding of young infants is that it can interfere with breastfeeding. Evidence shows that the introduction of other sources of calories results in a reduced intake of breast milk [24]. This substitution is likely to result in a reduction of the immunological benefits from the mother's milk.
It will not be surprising if the findings from this meta-analysis are used to justify food-distribution programmes concerned with young children. However, as we have argued elsewhere [25], evaluation of the merits of these programmes must be placed within the context of national social policies, particularly in developing countries. Food assistance will not compensate for the inefficiency of an educational or a health system, and their existence alone does not define a government's concern for the development of human potential.
Data collection and analyses were supported by NIH grant HD22440 and by Pew Charitable Trusts grant 9000210-000.