Early childhood growth, cognitive function and school achievement in late childhood

Abstract

Background: Children in lower- and middle-income countries often do not achieve their full developmental potential and tend to have lower academic performance compared to those in high income countries. Early childhood growth is linked with cognitive function or school achievement. This evidences mainly examine early childhood growth using height/length or stunting at specific points in time, but this approach fails to capture the dynamic nature of early childhood linear growth. Additionally, the relationship of fat mass (FM) and fat-free mass (FFM) with cognitive function during late childhood remains underexplored. Thus, this PhD study aims to examine the association of early childhood linear growth velocities and trajectories with cognitive function and school achievement. Furthermore, this study also aims to examine the association of FM and FFM accretion during early childhood with and cognitive function in late childhood. Methods: The papers presented in this thesis are based on data from the Infant Anthropometry and Body Composition birth cohort, which enrolled term newborns and invited them for 14 visits from birth to 10 years of age. Length/height and body composition data were collected during these visits, except for body composition between 6 months and 4 years. The outcome variables were school achievement and cognitive function, measured at the 10-year follow-up. School achievement was assessed using two markers: Math, English, and Science (MES) combined scores, and grade-for-age. Cognitive function was measured using the Peabody Picture Vocabulary Test (PPVT). Advanced modeling techniques -linear spline mixed-effect model and latent class trajectory analysis- were used to model early childhood growth. Regression analyses assessed associations of early childhood growth with cognitive function, MES scores and grade-for-age. Result: At the 10-year follow-up, 355 children were participated: 318 completed the PPVT test, 343 provided grade data, and 276 had MES scores. A 1 SD (standard deviation) increase in birth length was associated with 1.42 (95% CI: 0.99, 2.03) higher odds of achieving a high MES combined score, while a 1 SD increase in birth FFM was associated with a 0.14 SD (95% CI: 0.01, 0.28) higher PPVT. Postnatal FFM accretion from 0-3 and 3-6 months were associated with PPVT, (β = 0.50 (95% CI: 0.08, 0.93)) and (β = -0.48 (95% CI: -0.90, -0.07)), respectively. Additionally, linear growth velocity from 6-24 months was associated with appropriate grade-for-age, adjusted odds ratio (aOR) = 1.66 (95% CI: 1.14, 2.43). Four distinct height-for-age z score (HAZ) 11 trajectories were identified, with dynamic growth observed through 6 months and continuing until 2 years. Only the rising trajectory, which constitute 8.6% of the population, showed a HAZ trajectory above, but close to the WHO child growth standard median value. Furthermore, only this trajectory showed a positive association with cognitive function, the MES combined score, and grade-for-age, compared to the increasing-decreasing trajectory (β = 0.12 (95% CI: -0.24, 0.47), β = 4.54 (95% CI: -0.45, 9.55), aOR = 2.40 895% CI: 1.12, 5.15), respectively). Stunting at ages 4 and 6 were negatively associated with MES combined scores (aOR = 0.43 (95% CI: 0.20, 0.93) and aOR = 0.31 (95% CI: 0.11, 0.89), respectively). Stunting at age 2 was also inversely associated with appropriate grade-for-age, aOR = 0.39 (95% CI: 0.18, 0.88). Conclusion: Dynamic growth was observed during the first two years. The vast majority of children were shorter than the WHO child growth standards. Birth length and FFM at birth were positively associated with MES combined score and cognitive function, respectively. Furthermore, higher linear growth velocity from 6-24 months was associated with greater odds of being in the appropriate grade-for-age, while stunting after 2 years was negatively associated with school achievement. FFM from birth to 3 months and from 3-6 months showed opposite associations with cognitive function. This study underscores the importance of prenatal growth and early growth up to the age 2 years, for better cognitive function and school achievement. Therefore, programs aimed at improving cognitive function and school achievement should also focus on supporting child growth during these crucial periods.