Article by Melissa J Palmer and Richard J Silverwood, London School of Hygiene and Tropical Medicine (MethodsNews Spring 2015)
Children from more deprived backgrounds are more likely to be overweight and shorter in stature. Average birth weight also differs by socioeconomic status. Could birth weight thus play a mediatory role in the relationship between social disadvantage and childhood growth? We recently reviewed the evidence for this in the literature.
The existence of social inequalities in health is well established; poor health disproportionately burdens those of lower socioeconomic status. There is evidence to suggest that the early years of development play a critical role in the creation of socioeconomic health inequalities which are maintained into adulthood. As a result, researchers have highlighted the need for a greater focus on this critical period in infancy and childhood.
Studies conducted in Britain provide convincing evidence that such inequalities in health are reflected in the social patterning of childhood growth - specifically in obesity and height. The rate of childhood overweight and obesity is higher among children whose parents are of lower socioeconomic status, as indicated by measures of area-level deprivation, household income, parental occupation and educational level. Furthermore, children from more deprived backgrounds are generally shorter in stature compared with their less deprived counterparts.
Stature in childhood is often considered as a marker of development, and obesity in childhood is a well-established risk factor for obesity in adulthood and cardiovascular disease, cancer, and diabetes. The increasing prevalence of obesity is recognised as a major public health issue, and since the turn of the Millennium increases in the prevalence of childhood obesity in Britain have been especially pronounced among poorer communities.
Whilst a reduction in socioeconomic inequality itself would be one obvious solution to reducing the resultant differences in growth, a better understanding of the mediatory pathways through which the effects of deprivation act might give rise to alternative, possibly more achievable, interventions.
Lower birth weight has been found to be associated with lower socioeconomic status, while greater weight at birth is predictive of increased height and BMI in childhood. Therefore, it is conceivable that birthweight might play a mediatory role in the associations observed between deprivation and childhood growth – accounting for birth weight may potentially weaken the association with height, while strengthening the association with overweight/obesity.
While many studies concerned with the association between socioeconomic status and childhood growth make adjustment for birth weight, few allow for an explicit examination of the extent of mediation. We identified only one British study which did so. In this study, the strength of the association between deprivation and obesity increased markedly once adjustment was made for the effect of birthweight, consistent with our hypothesis of a mediatory role.
Future research should not only seek to examine the associations that exist between deprivation and childhood growth, but also elucidate the mediatory pathways though which inequalities are translated into physical health.