Trends in socioeconomic inequalities in underweight and obesity in 5-year-old children, 2011–2018: a population-based, repeated cross-sectional study

OBJECTIVE: To explore trends in prevalence and socioeconomic inequalities in underweight and obesity in 5-year-old schoolchildren in Scotland between 2011/2012 and 2017/2018. DESIGN: A population-based, repeated cross-sectional study. SETTING: Local authority primary schools in Scotland. PARTICIPANTS: 373 189 5-year-old schoolchildren in Scotland between 2011/2012 and 2017/2018. METHODOLOGY: Trends in prevalence and inequalities in underweight and obesity were examined across seven school years (2011/2012–2017/2018) for 373 189 5-year-old schoolchildren in Scotland. Body mass index SD scores were calculated, and epidemiological cut-offs relative to the UK 1990 references categorised underweight and obesity. Slope/relative indices of inequality (SII/RII) were calculated for underweight and obesity by school year using the area-based Scottish Index of Multiple Deprivation. RESULTS: The prevalence of obesity rose slightly overall during the study period (9.8% in 2011/2012; 10.1% in 2017/2018). However, this masked a widening of inequalities, with children from the most deprived areas experiencing a greater risk of obesity in 2017/2018 than in 2011/2012 (risk ratio=1.14, 95% CI 1.04 to 1.25) compared with an unchanged risk in children from the least deprived areas (risk ratio=0.95, 95% CI 0.82 to 1.11). SII and RII indicate widening inequalities for obesity, with RII rising from 1.95 (95% CI 1.71 to 2.22) in 2011/2012 to 2.22 (95% CI 1.93 to 2.56) in 2017/2018. The prevalence of underweight was consistently low (compared with the UK 1990 references) and remained unchanged over the study period (1.2% in 2011/2012; 1.1% in 2017/2018), with no consistent evidence of social patterning over time. CONCLUSIONS: Inequalities in obesity in schoolchildren in Scotland are large and have widened from 2011, despite only a slight rise in overall prevalence. In contrast there has been little change in underweight prevalence or inequalities during the study period. Extra resources for policy implementation and measures which do not widen inequalities and focus on reaching the most deprived children are required to tackle the high prevalence and growing inequalities in childhood obesity in Scotland.