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

Abstract

Background: Socioeconomic 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 findings: The 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.

Conclusions: Socioeconomic 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.

Fig 1. Trends for Obesity^a by Sex and Age Group by Area-level Deprivation^b England, 2007–2008 to 2011–2012^c.

^a Obesity for youth aged 4 to 11 defined as having a body mass index (BMI) at or above the age and sex-specific 95^th centile on the UK 1990 Growth Reference. ^b Index of Multiple Deprivation (IMD) 2010 score derived from lower super output (LSOA) area of the child’s residence in 2007.^c Dashed lines indicate the 10 to 11 year old age group. ^d Data from the National Child Measurement Programme.

Fig 2. Kernel density graph of zBMI and the difference in zBMI (95% confidence interval for difference) for the least and most deprived groups in 2007 to 2008 and 2011 to 2012 for boys and girls 4 to 5 years of age.

Vertical dashed lines on kernel density graphs show the UK 1990 definitions for underweight (2^nd centile), overweight (85^th), obesity for population monitoring (95^th), obesity for clinical classifications (98^th) and morbid obesity (99.6^th).

Fig 3. Kernel density graph of zBMI and the difference in zBMI (95% confidence interval for difference) for the least and most deprived groups in 2007 to 2008 and 2011 to 2012 for boys and girls 10 to 11 years of age.

Vertical dashed lines on kernel density graphs show the UK 1990 definitions for underweight (2^nd centile), overweight (85^th), obesity for population monitoring (95^th), obesity for clinical classifications (98^th) and morbid obesity (99.6^th).