Trends in Socioeconomic Inequalities in Body Mass Index, Underweight and Obesity among English Children, 2007-2008 to 2011-2012.

James White,Laust Hvas Mortensen,David Rehkopf,Jennifer L Baker

doi:10.1371/journal.pone.0147614

James White, Laust Hvas Mortensen + Show 2 more

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https://doi.org/10.1371/journal.pone.0147614

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Abstract

BackgroundSocioeconomic inequalities in childhood obesity have been reported in most developed countries, with obesity more common in deprived groups. Whether inequalities are found in the prevalence of underweight, the rest of the body mass index (BMI) distribution, or have changed across time is not clear.Methods and FindingsThe sample comprised 5,027,128 children on entry (4 to 5 years old) and leaving (10 to 11 years) state primary (elementary) school who participated in the National Child Measurement Programme (England, United Kingdom). We used area-level deprivation (Indices of Multiple Deprivation at the lower super output area) as a measure of socioeconomic deprivation. From 2007–2008 to 2011–2012 inequalities in obesity between the most compared to least deprived group increased (from 7.21% to 8.30%; p<0.001), whereas inequalities in the prevalence of underweight (1.50% to 1.21%; p = 0.15) were stable during this period. There were no differences by age group or by sex, but a three-way interaction suggested inequalities in obesity had increased at a faster rate for 10 to 11 year old girls, than 4 to 5 year old boys, (2.03% vs 0.07%; p<0.001 for interaction). Investigating inequalities across the distribution of zBMI showed increases in mean zBMI (0.18 to 0.23, p<0.001) could be attributed to increases in inequalities between the 50th and 75th centiles of BMI. Using the 2011 to 2012 population attributable risk estimates, if inequalities were halved, 14.04% (95% CI 14.00% to 14.07%) of childhood obesity could be avoided.ConclusionsSocioeconomic inequalities in childhood obesity and zBMI increased in England between 2007–2008 and 2011–2012. Inequalities in the prevalence of underweight did not change. Traditional methods of examining inequalities only at the clinical thresholds of overweight and obesity may have led the magnitude of inequalities in childhood BMI to be underestimated.

Highlights

A socioeconomic gradient in childhood obesity has been reported in most middle to high income countries with a greater prevalence in more disadvantaged groups [1,2,3,4]
Socioeconomic inequalities in childhood obesity and zBMI increased in England between 2007–2008 and 2011–2012
The funders had no role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript

Summary

Introduction

A socioeconomic gradient in childhood obesity has been reported in most middle to high income countries with a greater prevalence in more disadvantaged groups [1,2,3,4]. The traditional modelling of inequalities in overweight and obesity, typically using logistic regression [10, 28], or the mean of BMI in linear models [10], has the result that inequalities occurring at other parts of the frequency distribution are ignored While interpretation of this standard approach is simpler, it has two distinct limitations which sacrifices insights that can be made from examining inequalities across the entire BMI distribution. A lack of change in inequalities in mean BMI may hide substantial differences in the proportion of obese- and underweight individuals which could offset each other Despite these limitations of the standard approach, the evidence to date on inequalities in childhood body mass index has concentrated almost exclusively on only the higher centile thresholds of overweight and obesity [5,6,7,8,9,10,11,12,13,14]. Whether inequalities are found in the prevalence of underweight, the rest of the body mass index (BMI) distribution, or have changed across time is not clear

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