Life Course Social Inequalities in Body Composition: Understanding the Role of Child Behavioural and Emotional Problems and the Environment

Despite life course inequalities in body mass index (BMI) being well studied, less is known about inequalities in body composition. There is also a lack of understanding regarding the role psychological characteristics, and the environment in which people live, play in the development of inequalities. Firstly, a systematic review was conducted to summarise the evidence on the association between socioeconomic position (SEP) and body composition. Secondly, data from the Millennium Cohort Study (MCS), a cohort of 19,517 children born in 2000/2, were used. Growth curve models were applied to investigate inequalities in trajectories of fat mass index (FMI), fat-free mass index (FFMI) and their ratio (FM:FFM). Structural equation modelling (SEM) was used to investigate mediators (internalising and externalising symptoms) of associations between SEP with body composition and BMI in adolescence, and to test moderation of mediating paths by environmental conditions (area-deprivation, green space density, fast-food and domestic garden density). The systematic review found lower SEP related to higher fat mass (FM) and less consistent evidence of lower SEP related to lower fat-free mass (FFM) in high-income countries. Inequalities were more common among children compared to adults, and more common in females compared to males, except for inequalities in FFM in childhood. In the MCS those in more disadvantaged SEP in infancy had higher FMI and FM:FFM age 7, and inequalities widened to age 17. Social inequalities in FMI and FM:FFM at age 17 were mediated by internalising symptoms, and for FFMI and BMI internalising and externalising symptoms jointly mediated associations. For FMI, FM:FFM and BMI – the mediation through internalising symptoms was greatest among those living in the least green and most deprived areas. In order to improve childhood and adolescent body composition, early life disadvantage should be addressed and improvement of the environment in disadvantaged areas considered