Infantile growth velocity and later asthma/ wheeze: GENESIS and the Healthy Growth Study

Accumulating evidence suggests that wheezing illnesses have at least part of their origin in the infantile period, wherein septal restructuring and alveolar formation ensue. Therefore, throughout infancy, genetic and environmental factors could affect bronchial development and future airway function. On this basis, we hypothesised that differential growth velocity, within the first 6 months of life, could be diversely linked to paediatric wheezing illnesses. Establishing such an interaction still eludes us, due to limited and conflicting evidence [1–6] and age-specific differences in bronchial function/structure [3]. We, therefore, opted to investigate a potential correlation in two populations of children of different ages, the Growth, Exercise and Nutrition Epidemiological Study In preSchoolers (GENESIS) study and the Healthy Growth Study cohorts (preschool and late childhood, respectively); thereby, we also appraised any age-definable discrepancies. These cross-sectional studies involved children aged 2–5 years attending nurseries in five Greek counties (GENESIS study) [7] and children aged 9–13 years, attending primary schools in four Greek counties (Healthy Growth Study) [8]. Sampling of nurseries/schools was stratified by parents’ educational level and total student population in the respective municipality and their selection was random, as previously described [7, 8]. By using the parents’ educational level as a proxy for socioeconomic level (SEL), we opted to compile a sample that was largely representative of the SEL level of Greek children. Specifically, municipalities were classified in three categories of different SELs i.e. Higher, Medium and Lower (Census 2001 [9]). Subsequently, certain municipalities were randomly selected from each one of these three SEL groups; their number was proportional to the size of each group’s preschool/pre-adolescent population. Finally, schools were randomly selected from each municipality; their number was proportional to the municipality’s schoolchildren population. Parental consent was acquired and the studies were approved by the Greek Ministry of Education and the Ethics Committee of the Harokopio University, Athens, Greece. Socio-demographic and perinatal data was collected and body fat assessment/anthropometric measurements were conducted during school interviews. The parents provided the researchers with their children’s health books wherein (as part of standard practice in Greece) data from routine paediatrician-conducted measurements of infantile weight and length were recorded; this information was used to estimate weightfor-length z-scores based on the World Health Organization (WHO) growth charts. The z-score difference between birth and 6 months of age was used to classify children into the following categories: retarded growth velocity (f1 z-score difference), normal growth velocity (-1f1 z-score difference), and rapid growth velocity (.1 z-score difference). Potential atopic predisposition of the GENESIS participants was evaluated through the question: ‘‘Did a doctor ever tell you that your child has atopic dermatitis?’’. Asthma outcomes were defined from the International Study of Asthma and Allergies in Childhood (ISAAC) core questionnaire. 1) Current wheeze (did your child have wheezing or whistling in the chest in the past 12 months?). 2) Ever wheeze (did your child have wheezing or whistling in the chest at any point in time?). 3) Asthma ever (did your child ever have asthma diagnosed by a doctor?). Complete data were available from 1668 children in the GENESIS study and 1867 children in the Healthy Growth Study. Univariate logistic regression analyses were conducted and followed by multivariate logistic regression analyses, whereby we adjusted for a wide array of potential confounding/intervening variables (table 1). The statistical package for social sciences (SPSS; IBM Corporation, Armonk, NY, USA), version 20.0 was used and a two-tailed p,0.05 was considered significant.