Early childhood body mass index growth and school readiness: A longitudinal cohort study

BACKGROUND: Child growth influences future health and learning. School readiness refers to a child's ability to meet developmental expectations at school entry. The association of early growth rate and patterns with school readiness remains unknown. OBJECTIVE: To determine the association of child body mass index (BMI) growth with school readiness in a cohort of young children. METHODS: A prospective cohort study (2015-2022) was conducted in children 0-6 years enrolled in the TARGet Kids! research network in Toronto, Canada. Two analytical approaches were used to measure growth using child weight and height/length data between 0 and 4 years: (i) age- and sex-standardised BMI (zBMI) growth rate per year using a piecewise linear model; and (ii) distinct zBMI trajectories using latent class mixed models. School readiness (4-6 years) was measured using teacher-completed Early Development Instrument (EDI). Robust Poisson models and marginal linear models using generalised estimating equations were used adjusting for confounders identified a priori. RESULTS: In this study of 1077 children (mean age at EDI completion: 4.8 years; 52.6% male) with 6415 zBMI measurements, mean growth rate was 0.65 zBMI units/year (0-2 years) and -0.11 zBMI units/year (2-4 years). Two distinct zBMI trajectories were identified: the stable trajectory and the catch-up trajectory. There was insufficient evidence that zBMI growth rates (risk ratio 1.10, 95% confidence interval 0.78, 1.55 for 0-2 years; risk ratio 0.71, 95% confidence interval 0.32, 1.57 for 2-4 years) or trajectories (risk ratio 1.05, 95% confidence interval 0.82, 1.35, catch-up trajectory vs. stable trajectory) were associated with school readiness. CONCLUSIONS: No association was found between BMI growth and school readiness. School readiness may be more impacted by factors directly related to obesity or adiposity at the time of EDI measurement rather than growth.