ORIGINAL ARTICLE Interaction of zinc or vitamin A supplementation and specific parasite infections on Mexican infants’ growth: a randomized clinical trial JL Rosado 1,6 , MC Caaman ˜o 1,6 , YA Montoya 2 , M de Lourdes Solano 3 , JI Santos 4 and KZ Long 5 1 School of Natural Sciences, Universidad Auto´noma de Quere´taro, Mexico; 2 Centro de Salud para Infancia y Adolescencia, Secretarı´a de Salud, Mexico City, Mexico; 3 Instituto Nacional de Ciencias Me´dicas y Nutricio´n ‘Salvador Zubiran, Mexico City, Me´xico; 4 Department of Experimental Medicine, School of Medicine, Universidad Nacional Autonoma de Mexico, Mexico City, Mexico; 5 Nutrition, Disease Control and Injury Unit, School of Population Health, University of Queensland, Australia and 6 Nutrition, CINDETEC, Queretaro, Mexico Background: The efficacy of micronutrient supplementation on growth may be modified by specific gastrointestinal parasite infections Methods: We carried out a double-blind placebo-controlled trial to evaluate the effect of vitamin A and zinc supplementation on gastro-intestinal pathogen infections and growth among 584 infants in Mexico City. Children aged 5–15 months were assigned to receive either a vitamin A supplement every 2 months (20 000 IU of retinol for infants p; 1 year or 45 000 IU for infants 41 year), a daily supplement of 20 mg of zinc, a combined vitamin A–zinc supplement or a placebo, and were followed up for 1 year. Weight and length were measured once a month and morbidity histories were recorded twice a week for 12 months. Monthly stool samples were screened for Giardia duodenalis, Ascaris lumbricoides and Entamoeba spp. Growth velocity slopes, generated from the linear regression of individual child length, and height-for-age z-scores on time were analyzed as end points in regression models, adjusting for the presence of parasite infections Results: The main effect of vitamin A supplementation was in height improvement (Po0.05), and was only found in the model evaluating infants with any parasite. There was an interaction effect of slower growth (Po0.05) found in infants infected with any parasite and supplemented with vitamin A in slower growth (Po0.05). In addition, the interaction of zinc supplementation and Giardia duodenalis or A. lumbricoides was associated with reduced growth (Po0.05). Conclusion: Gastro-intestinal parasite infections may modify the effect that zinc or vitamin A supplementation has on childhood growth. European Journal of Clinical Nutrition (2009) 63, 1176–1184; doi:10.1038/ejcn.2009.53; published online 22 July 2009 Keywords: vitamin A; zinc; parasites; growth; infants Introduction Childhood linear growth faltering continues to be an important problem in more marginalized regions of the developing world where children are exposed to a wide range of infectious diseases and have inadequate diets. Micronu- trient deficiencies may significantly contribute to such growth faltering, as strong associations between single or multiple micronutrient deficiencies and stunting have been reported (Allen, 1993; Rosado, 1998; Viteri and Gonzalez 2002). However, supplementation with specific micronutri- ents in randomized clinical trials has not always found a consistent effect (Bhandari et al., 2001). Zinc supplementa- tion has been found to be associated with significant improvements in linear and ponderal growth by Brown et al. (2002) in their meta-analysis of zinc supplementation trials. In contrast, Ramakrishnan et al. (2004) reported that vitamin A and iron supplementation did not improve child growth in a meta-analysis. The lack of effect for specific single micronutrient supplements may be because of the simultaneous presence of multiple micronutrient Received 12 June 2008; revised 3 March 2009; accepted 15 April 2009; published online 22 July 2009 Correspondence: Dr JL Rosado, School of Natural Sciences, University of Queretaro, Apartado Postal No 31, Desarrollo San Pablo, Queretaro, Mexico. E-mail: jlrosado@avantel.net Presented in part: Impact of vitamin A and zinc supplementation on growth among Mexican infants. Rosado JL, Caaman ˜o MC, Montoya YA, Frongillo E, Santos JI, Long KZ. Experimental Biology Meetings, San Franciso CA 2006. European Journal of Clinical Nutrition (2009) 63, 1176–1184 & 2009 Macmillan Publishers Limited All rights reserved 0954-3007/09 $32.00 www.nature.com/ejcn