Socioeconomic inequalities in childhood and adolescent body-mass index, weight, and height from 1953 to 2015: an analysis of four longitudinal, observational, British birth cohort studies

Background Socioeconomic inequalities in childhood body mass index (BMI) have been repeatedly documented in high income countries, yet there is uncertainty regarding how they have changed across time, how inequalities in the composite parts of BMI have changed (weight and height), and whether inequalities differ in magnitude across the outcome distributions. We investigated socioeconomic inequalities in childhood/adolescent weight, height, and BMI from 1953 to 2015 using British birth cohorts born in 1946, 1958, 1970, and 2001. Methods Associations between childhood social class and anthropometric outcomes at age 7, 10/11 and 14/16 years were examined to assess socioeconomic inequalities in each cohort using gender-adjusted linear regression models. Multilevel models were used to examine if these inequalities widened or narrowed from childhood to adolescence; quantile regression was used to examine whether the magnitude of inequalities differed across the outcome distribution. Findings Lower social class was associated with lower childhood/adolescent weight in earlier-born cohorts (1946-1970), yet with higher weight in the 2001 cohort. Lower social class was associated with shorter height in all cohorts, yet the absolute magnitude of this difference narrowed across generations. There was little inequality in childhood BMI in the 1946–1970 cohorts, yet inequalities were present in the 2001 cohort, and in all cohorts at 14/16 years (p<0.05 age x social class interactions). BMI and weight inequalities were larger in the 2001 cohort and systematically larger at higher quantiles—eg, in the 2001 cohort at 11 years there was a 0.98kg/m2 difference (0.63, 1.33) in median BMI (lowest to highest social class), yet 2.54kg/m2 (1.85, 3.22) difference at the 90th BMI percentile. Interpretation In the later 20th and early 21st centuries, socioeconomic inequalities in weight reversed, those in height narrowed, while inequalities in BMI and obesity emerged and widened. These drastic changes highlight the powerful impact of societal changes on child-adolescent growth and the insufficiency of previous policies in preventing obesity and its socioeconomic inequality. New and effective policies are required to reduce BMI inequalities in current and future children and adolescents. Without effective interventions, it is anticipated these inequalities will widen further throughout adulthood.