The impact of early childhood nutritional status on cognitive development : does the timing of malnutrition matter?

 77347 the world bank economic review, vol. 15, no. 1 81–113 The Impact of Early Childhood Nutritional Status on Cognitive Development: Does the Timing of Malnutrition Matter? Paul Glewwe and Elizabeth M. King This article uses longitudinal data from the Philippines to examine whether the timing of malnutrition in early childhood is a critical factor in determining subsequent cogni- tive development. Although some observers have argued that the first six months of life are the most critical in the sense that malnutrition during that time period harms cognitive development more than malnutrition later in life, analysis of the Philippines data does not support this claim. To the contrary, the data suggest that malnutrition in the second year of life may have a larger negative impact than malnutrition in the first year of life. As developing countries have been making greater efforts to improve educational outcomes, policymakers are paying more attention to the role that child nutri- tion may play in both improving school readiness and increasing learning (see Young 1997 for a review). In many developing countries one third or even one half of all children are seriously stunted—height for age is two standard devia- tions or more below the World Health Organization reference median—before they enroll in primary school (unicef 1996). If poor nutrition does indeed im- pair educational performance, these high rates of malnutrition in the first years of life imply that a large proportion of children in these countries begin school with a serious learning handicap. A growing literature documents the sizable correlation between childhood nutrition and school performance; however, evidence on the causal nature of this association is sparse, variable in quality, and often inconclusive. A few re- cent studies have examined the causal links by explicitly addressing underlying behavioral assumptions (see Alderman and others 1997, Behrman and Lavy 1994, and Glewwe and Jacoby 1995), yet none focus on a key aspect of the relation- Paul Glewwe is with the Department of Applied Economics at the University of Minnesota, and Elizabeth M. King is with the Development Research Group at the World Bank. This article was written while Paul Glewwe was with the Development Research Group at the World Bank. The authors’ e-mail addresses are pglewwe@apec.umn.edu and eking@worldbank.org. This project was funded by World Bank Research Committee Grant 679-57, with additional funding from the Asian Development Bank. The authors would like to thank Nauman Ilias and Azot Derecho for excellent research assistance and the team of the Office of Population Studies (Cebu, Philippines) for their help with data questions. They also would like to thank Linda Adair, Hanan Jacoby, T. Paul Schultz, and four anonymous referees for helpful comments. © 2001 The International Bank for Reconstruction and Development / THE WORLD BANK 81 82 the world bank economic review, vol. 15, no. 1 ship between nutrition and school performance: does the timing of malnutrition during the first years of life matter? Nutritionists and physiologists began to examine the issue of timing in the 1970s. Some argue that the time from early gestation to the first six months of life is the most critical for brain development, implying that inadequate nutri- tion during this period would have much more severe effects on children’s cog- nitive development than would subsequent episodes of malnutrition. Recent research has raised doubts about these claims. Nonetheless, the question itself is of considerable policy interest because the existence of a critical period implies that nutritional interventions are most effective when administered during that period. In this article we use a longitudinal data set, the Cebu Longitudinal Health and Nutrition Survey (clhns), to examine the question of timing. I. Early Childhood Nutrition and School Performance: A Brief Review of the Literature Studies that link child nutrition and school performance typically show that malnutrition is correlated with poor school performance. But most of these studies do not test for causality, that is, whether poor nutrition causes poor school per- formance (see Grantham-McGregor 1995, Behrman 1996). Because disadvan- taged children are more likely to be both undernourished and weak students, it is not clear whether their poor performance in school is primarily due to poor nutrition or to other aspects of their disadvantaged circumstances. A few experimental and quasi-experimental studies generally support the hypothesis that causality runs from poor nutrition to poor school performance (Gorman 1995, Pollitt et al. 1995). Yet little is known about the mechanisms and processes that govern this causality, which hampers efforts to design more effective nutrition policies. The most likely pathways involve the effects of inad- equate intake of calories, protein, and specific micronutrients on cognitive de- velopment, which in turn affect school readiness and performance. A crucial unanswered question regarding the impact of childhood nutrition on educational outcomes is the relationship between the timing of early child- hood malnutrition and subsequent school performance. Some nutritionists and child physiologists claim that there is a “critical period