Weight status trajectories and trends in height and BMI of schoolchildren: a cohort study

Abstract Understanding trends in height and BMI, along with trajectories of weight status, is crucial to identifying the optimal timing for intervention. The objective of this study was to describe trends in height and BMI among children and adolescents and identify the trajectory of weight status over time. This was a longitudinal study with data collected annually (2013–2020). A total of 41 325 students aged 5–18 years from forty-seven schools participated in the study, and a subsample of 11 535 participants with at least five BMI measurements was used for the analyses. Mixed-effects analysis showed significant increases in height over the years for boys (0·19 cm, standard error 0·01, P < 0·001) and girls (0·15 cm, standard error 0·01, P < 0·001). Regarding BMI, an increasing trend over the years was also found in boys (0·04 kg/m 2 , se 0·01, P < 0·001) and girls (0·04 kg/m², se 0·01, P < 0·001). Analysing weight status trajectories, three groups were identified: consistently normal weight (males 63·7 %, females 64·5 %), increasingly overweight (males 21·8 %, females 20·7 %) and increasingly obese (males 14·5 %, females 14·8 %). We conclude that in adolescence, height was below expected, indicating that children are not reaching their maximum growth potential. Furthermore, the identification of increasing trajectories of overweight and obesity, starting in childhood, emphasises the progressive nature of excessive weight gain before adulthood. These findings highlight the early onset of nutritional deviations in this population, suggesting the need for interventions to promote healthy weight as children transition into adolescence to mitigate future health risks.