Obesity in early life remains a leading public health challenge because it is linked to long-term poor physical and mental health. Although some data suggested that increases in the prevalence of obesity among primary school children had stalled in the early 2000s, recent studies report that the prevalence of obesity among children and adolescents has continued to increase.

Therefore, to understand how the public health challenge of childhood obesity is evolving, and consequently the long-term prospects for population health, it is important to investigate temporal changes in incidence at the national level. In the study published in the journal Pediatrics, researchers examined changes in the incidence of obesity among cohorts of US children growing up 12 years apart, going through the same developmental stages at different points in time: 1 cohort in the late 1990s to early 2000s, the other in the 2010s. 

For the study, 2 parallel nationally representative kindergarten cohorts with direct anthropometric measurements at multiple points from the average age of 6 years to 11 years were used. These 2 cohorts were enrolled using the Early Childhood Longitudinal Studies. The study also investigated the annualized incidence rate and cumulative incidence proportion of obesity (BMI z-score ≥95th percentile based on Centers for Disease Control and Prevention weight-for-age z-scores).

On analyzing the data collected from the 2 cohorts, it was observed that there was a 4.5% relative increase in cumulative incidence of new obesity cases by end of fifth grade among children who did not have obesity at kindergarten entry. However, no substantial changes in the annual incidence were observed. The risk of incident obesity for children who had normal BMI at kindergarten entry stayed the same, but the risk of incident obesity among overweight kindergartners increased slightly. 

Additionally, social disparities in obesity incidence expanded: incidence of new cases during primary school among non-Hispanic Black children increased by 29%, whereas the risk for other race-ethnic groups plateaued or decreased. Children from the most socioeconomically disadvantaged households experienced 15% higher cumulative incidence across the primary school in 2010 than in 1998.

Hence, based on these findings it can be inferred that approximately 40% of high school students and young adults experienced obesity or were overweight before leaving primary school. Young people who were born in the 2000s experienced obesity incidence at even higher levels, at younger ages, and higher severity during the developmentally important stages of childhood, compared even with the cohort 12 years earlier. 

Source: Pediatrics. 2022 Aug 1;150(2):e2021053708. doi: 10.1542/peds.2021-053708.