|Effects of Improved Nutrition in Early Childhood : The institute of Nutrition of Central America and Panama (INCAP) Follow-up Study; Proceedings of an IDECG workshop, July 1990, Bellagio, Italy, Supplement of The Journal of Nutrition (International Dietary Energy Consultative Group - IDECG, 1994, 198 pages)|
|Nutritional impact of supplementation in the INCAP longitudinal study: Analytic strategies and inferences(¹,²)|
JEAN-PIERRE HABICHT,*³ REYNALDO MARTORELL AND JUAN A. RIVERA
*Division of Nutritional Sciences, Cornell
University, Ithaca, NY 14853-6301, Departament of International Health,
The Rollins School of Public Health of Emory Unioersih, Atlanta, CA 30322, and
Centro de Inuestigaciones en Salud Pública, Instituto Nacional de Salud
Pública, 62508 Cuernavaca, Morelos, México
¹ Presented in the symposium on Nutrition in Early Childhood and its long-term Functional Significance, FASEB, April 6, 1992, Anaheim, CA. Published as a supplement to The Journal of Nutrition. Guest editors for this supplemental publication were Reynaldo Martorell, The Rollins School of Public Health of Emory University, Atlanta, GA, and Nevin Scrimshaw, The United Nations University, Boston, MA.
² The INCAP longitudinal study was supported by contract No. HD-5-0640 from the National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland. Additional sources of support were from the Agency for International Development, Washington, DC (AID-TAC/1224) and a grant from Rockefeller Foundation (73030-E7352). The follow-up study was supported by RO1 grant HD-22.440.
³ To whom correspondence should be addressed: Division of Nutritional Sciences, 210 Savage Hall, Cornell University, Ithaca, NY 14853-6301.
From 1969 to 1977 a supplementation trial was conducted in Guatemala to ascertain the effects on physical and behavioral outcomes of improved nutrition in pregnant women and in preschool children. This paper reviews different strategies to analyze the effect of the intervention on physical growth. One strategy compares outcomes in two villages that were randomly allocated to receive Atole, a supplement containing high amounts of protein and energy, with values in two other villages that received Fresco, a beverage containing no protein and little energy. Both supplements contained micronutrients. This comparison of village means gives a probability significance statement (P<0.005) that the difference in growth was because of the supplement intervention, although it does not specify the aspect of the intervention that caused the effect. Complementary strategies increase the credibility that the effect of the supplement was nutritional. Thus analysis of the dose response with increasing supplement intake within the villages excludes the possibility that the above findings were the result of knowing which villages received which supplement (i.e., measuring biases). A greater effect in those most likely to respond nutritionally also increases the credribility that the mechanism was nutritional. In studying other behavioral and biomedical impacts of this supplementation intervention, analyses for credibility should always be included. J. Nutr. 125: 1042S-1050S, 1995.
INDEXING KEY WORDS:
· analytic methods
The study population, the experimental design and the methods used in the INCAP longitudinal study 1969-77) are described elsewhere (Martorell et al.1995). In summary, two kinds of supplements were distributed in a central refectory in four villages, in midmorning and midafternoon, to any villager who attended. Supplement consumption was recorded for infants, children < 7 y of age and pregnant and lactating women. From 1969-1977, two of the villages received a high-protein, high-energy supplement called "Atole" and the other two were given a no-protein, low-energy supplement called "Fresco." The villages were paired by size (i.e., large and small) and allocation within pairs to the supplements was random. From 1971 to 1977, the supplements had the same concentrations of specified micronutrients.
Growth and behavior, the key outcomes in children, were assessed periodically during the preschool period, as were measurements of potential modifiers or confounders such as morbidity, home diet and socioeconomic status. Maternal nutrition and health information also was collected periodically during pregnancy and lactation.
This paper presents different approaches to the analysis of the impact of supplementation on physical growth. These approaches may be divided into those that took advantage of the randomized design and those that sought other ways to control for confounding. The analyses selected as examples are tests of the effect of the supplement type on growth in length by three years of age, the effect of different amounts of maternal supplementation during pregnancy on birth weight and the effect of supplementation on improving weight in wasted children.
Except for the effect on growth presented in Table 1, all the findings discussed have been published elsewhere and are appropriately cited.