Since the post-war period, socioeconomic inequalities in children’s weight have reversed in the UK – with disadvantaged children originally being more likely to be thinner than more advantaged children, but now typically being more likely to be overweight or obese, according to an observational study.
Previously, studies of this kind have analyzed trends in body mass index (BMI), but not height and weight separately; this study is the first to disentangle the changes behind increasing BMI inequalities over time.
Between 1953 to 2015, the difference in children’s BMI levels between the most and the least disadvantaged children has expanded, however, the difference in children’s height has narrowed, and fewer disadvantaged children are now of short stature.
Authors of the study, published in the Lancet Public Health Journal, say that these trends highlight the powerful influence that the obesogenic environment has had on socioeconomically disadvantaged children, with and the failure of decades of previous policies to prevent obesity and related socioeconomic inequalities.
“Our findings illustrate a need for new effective policies to reduce obesity and its socioeconomic inequality in children in the UK – previous policies have not been adequate, and existing policies are unlikely to be either. Without effective interventions, childhood BMI inequalities are likely to widen further throughout adulthood, leading to decades of adverse health and economic consequences,” says the lead author Dr. David Bann, UCL, UK.
“Our results illustrate a need for strong additional legislative changes that focus on societal factors and the food industry, rather than individuals or families. Bold action is needed, such as creating further incentives for food manufacturers to reduce sugar and fat content in food and drinks, reduce the advertising of unhealthy foods to children and families, and incentivize the sale of healthier alternatives. The Soft Drinks Industrial Levy is a positive but likely very limited step in the right direction”
The study included data for children born in England, Scotland and Wales from four longitudinal birth cohort studies beginning in 1946, 1958, 1970 and 2001. In the paper, 22,500 children were assessed at the age of 7 years, 34,873 were assessed at the age of 11, and 26,128 were assessed at the age of 15.
Between the ages of 7, 11 and 15 years, the children’s height and weight were measured, and BMI was calculated. The child’s father’s occupation was used as a marker of their socioeconomic position, and the association between socioeconomic position and weight was also analyzed from childhood and adolescence.
On average, the 2001 cohort was taller, heavier and had a higher BMI than the earlier born cohorts.
In all cohorts, the most disadvantaged children tended to be shorter than the least disadvantaged children. However, the difference narrowed over time – with the most disadvantaged 7-year olds being 3.9cm shorter than the least disadvantaged children in the 1946 cohort, whereas the difference in children in the 2001 cohort was 1.2cm.
At the same time, differences in weight reversed, with the lower socioeconomic position being associated with lower childhood and adolescent weight in the 1946, 1958 and 1970 cohorts, but with higher weight in the 2001 cohort. For example, the most disadvantaged 11-year olds weighed 2kg less than the least disadvantaged children in the 1946 cohort, however in the 2001 cohort, the most disadvantaged 11-year olds weighed 2.1kg more than the least disadvantaged children.
As a result of the weight and height changes, BMI inequalities were larger and appeared earlier in childhood in the 2001 cohort than in the earlier-born cohorts. In the 2001 cohort, the most disadvantaged 7-year olds had a BMI that was 0.5 kg/m2 greater than the least disadvantaged children.
Inequalities generally widened with age. By the age of 15 years, BMI inequalities were present across all cohorts except the 1946 cohort and were largest in the 2001 cohort (1.4 kg/m2 difference between the most and least disadvantaged teenagers, compared with a difference of 0.4kg/ m2 and 0.6 kg/m2 for the 1958 and 1970 cohorts, respectively).
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Explaining the differences in childhood height, weight and BMI since the post-war period, the authors point to the considerable changes to diets and physical activity levels in Britain.
These include the end of wartime rationing in 1954 when diets typically included higher consumption of vegetables, and lower consumption of sugar and soft drinks. Since that time, the food environment has become increasingly obesogenic, and society has become more unequal, which may have particularly impacted on the access to healthy foods among socially disadvantaged families, resulting in increased childhood BMI among these groups. In addition, inequalities in adult BMI emerged in the 1980s and may have contributed to childhood BMI changes, as parents’ and children’s BMI are associated.
The authors note some limitations, including that most children enrolled were white, so the findings cannot be generalized to all ethnic groups in Britain. They also note that dropout rates were higher in more disadvantaged children, which could result in BMI inequalities being under or overestimated.
As BMI does not account for the level of fat, it may be an inexact measure of obesity and could have led to healthy children being miscategorized as overweight or obese. Lastly, the father’s occupation is only one aspect of the socioeconomic position, although the results remained the same when repeated using the mother’s education level.
Informatively, this study was funded by Cohorts and Longitudinal Studies Enhancement Resources’ (CLOSER), a collaborative research programme funded by the UK Economic and Social Research Council, Medical Research Council and based at the UCL Institute of Education and was additionally supported by the Academy of Medical Sciences/the Wellcome Trust. It was conducted by researchers from UCL and Loughborough University.