The Age-Varying Association Between BMI and Height-for-Age in Vietnamese Schoolchildren: A Sex-Stratified Quantile Regression Study
- 1Vinmec International Hospital
Abstract
BackgroundBMI and height are usually related through mean-based models, which can mask how this relationship varies across the height distribution and across age. Whether BMI relates to height differently at different quantiles, and whether this differs by sex, is not well studied in Southeast Asian children.
MethodsWe analyzed longitudinal school health data from 32,006 Vietnamese children (16,489 boys, 15,517 girls) aged 5 to 18 with at least 3 annual visits from 2018 to 2025. Using sex-stratified linear quantile mixed models, we estimated the association between BMI-for-age Z-score (BMIZ) and height-for-age Z-score (HAZ) at 5 quantiles, adjusting for a flexible age spline and study site, with a child-level cluster bootstrap for inference, plus a pooled model with a formal sex interaction test.
ResultsA 1SD increase in BMIZ was linked to higher HAZ at every quantile in both sexes (boys 0.078 to 0.100, girls 0.055 to 0.089, all p < .01), with no significant sex interaction (p = .35), contrasting with a small negative association from a linear mixed model (-0.023). This association did not differ significantly across quantiles within either sex, pointing to a fairly uniform effect across the height distribution itself, but it did vary strongly by age, strongest in early and mid-childhood and reversing to negative by late adolescence in both sexes, so children with overweight or obesity were taller for age through most of childhood but shorter than leaner peers by the oldest ages studied. Within-group variability in HAZ narrowed with age in both sexes, and boys with thinness showed a consistently wider height spread than boys in the other BMI categories through most of childhood, a pattern that was less pronounced in girls.
ConclusionsBMIs association with linear growth in Vietnamese children is positive through most of childhood but weakens and reverses by late adolescence, a pattern mean-based models obscure. BMI and height should be interpreted together in light of a childs age, not as one fixed relationship.
Related
- Conditional Growth References for Vietnamese Children: Quantile Regression of Growth Distributions and Phenotypes
- Heterogeneous association between maternal haemoglobin concentration and child haemoglobin levels: a quantile regression analysis using multi-country nationally representative data.
- Prevalence, Predictors, and Persistence of Inadequate Spectacle Correction in Vietnamese Schoolchildren
- Prepubertal Body Mass Index Reshapes the Distribution of Pubertal Growth Velocity in Vietnamese Children: A SITAR-Based Quantile Analysis
- Heterogeneous impact of health insurance on children’s nutritional status: insights from Instrumental Variable Quantile Regression (IV-QR) approach
BibTeX
@misc{ho2026agevarying,
title = {{The Age-Varying Association Between BMI and Height-for-Age in Vietnamese Schoolchildren: A Sex-Stratified Quantile Regression Study}},
author = {N. T. Ho},
howpublished = {medRxiv},
year = {2026},
month = sep,
doi = {10.64898/2026.09.08.26362487},
url = {https://www.medrxiv.org/content/10.64898/2026.09.08.26362487v1},
note = {CC BY-NC-ND},
}
RIS
TY - UNPB
TI - The Age-Varying Association Between BMI and Height-for-Age in Vietnamese Schoolchildren: A Sex-Stratified Quantile Regression Study
AU - N. T. Ho
PY - 2026
DA - 2026/09/08
PB - medRxiv
DO - 10.64898/2026.09.08.26362487
UR - https://www.medrxiv.org/content/10.64898/2026.09.08.26362487v1
AB - BackgroundBMI and height are usually related through mean-based models, which can mask how this relationship varies across the height distribution and across age. Whether BMI relates to height differently at different quantiles, and whether this differs by sex, is not well studied in Southeast Asian children. MethodsWe analyzed longitudinal school health data from 32,006 Vietnamese children (16,489 boys, 15,517 girls) aged 5 to 18 with at least 3 annual visits from 2018 to 2025. Using sex-stratified linear quantile mixed models, we estimated the association between BMI-for-age Z-score (BMIZ) and height-for-age Z-score (HAZ) at 5 quantiles, adjusting for a flexible age spline and study site, with a child-level cluster bootstrap for inference, plus a pooled model with a formal sex interaction test. ResultsA 1SD increase in BMIZ was linked to higher HAZ at every quantile in both sexes (boys 0.078 to 0.100, girls 0.055 to 0.089, all p < .01), with no significant sex interaction (p = .35), contrasting with a small negative association from a linear mixed model (-0.023). This association did not differ significantly across quantiles within either sex, pointing to a fairly uniform effect across the height distribution itself, but it did vary strongly by age, strongest in early and mid-childhood and reversing to negative by late adolescence in both sexes, so children with overweight or obesity were taller for age through most of childhood but shorter than leaner peers by the oldest ages studied. Within-group variability in HAZ narrowed with age in both sexes, and boys with thinness showed a consistently wider height spread than boys in the other BMI categories through most of childhood, a pattern that was less pronounced in girls. ConclusionsBMIs association with linear growth in Vietnamese children is positive through most of childhood but weakens and reverses by late adolescence, a pattern mean-based models obscure. BMI and height should be interpreted together in light of a childs age, not as one fixed relationship.
ER -