Neighbourhood Socio-economic Status and Aerobic Fitness in Children: A Longitudinal Study.

Background: Cardiorespiratory fitness (CRF) is an important marker of overall health in adulthood, and is strongly associated with morbidity and mortality. CRF tracks from childhood into adulthood; therefore, it is important to identify barriers to the development of CRF. Socio-economic status (SES) is associated with health outcomes and behaviour, and may impact CRF in children and adolescents. The purpose of this study is to determine whether there is an association between SES and CRF in children and adolescents. Methods: Data come from the Physical Health Activity Study Team (PHAST) project, a longitudinal cohort study of children conducted between 2004-2010. The target population included all children in the fourth grade enrolled in the public school system in the Niagara region of Ontario, Canada. The Léger 20-m shuttle run test was used as a field-based measure of fitness. SES was assessed using the median income in the 2011 Canadian census in the dissemination area (DA) of residence as a proxy for household income. Growth curve modeling characterized change in fitness over time. Model 1 included sex, age at each assessment, and the interaction of these terms. Model 2 included DA and age as random effects. Neighbourhood income was added to this model. Finally, an interaction of the two variables was created to test whether the effect of neighbourhood SES changed with age. Results: Relative VO_2max declined with age for both sexes (coefficient=-0.61, p<0.001), but did so more rapidly among females (coefficient=-2.47, p<0.001). DA income was highly significant when added to the model (coefficient=0.53, p<0.001), indicating an overall difference between residents of wealthier and poorer neighbourhoods. The interaction of DA median income and age was not significant. Discussion: The findings from this study indicate that a SES income gradient exists for aerobic fitness, which is already present at age 9, and does not change with age. This implies that an explanation might be sought in early-life influences on childhood CRF. The identification of disparities in fitness raises questions regarding social equity; that some children are more disadvantaged than others is an ethical, as well as a public health concern, that requires further research. [ABSTRACT FROM AUTHOR]