# Weight Trajectories Among Youths Following Residential Relocation

## TL;DR

Moving to greener, less polluted areas may help prevent unhealthy weight gain in children and adolescents, though effects vary by location.

## Contribution

The study introduces a novel approach to understanding how residential relocation and environmental factors influence BMI trajectories in children across different countries.

## Key findings

- Moving to areas with higher environmental hazards, like more pollution or less green space, was linked to increased z-BMI in Dutch and Swedish cohorts.
- Exposure to more gray space (urbanized areas) was consistently associated with higher z-BMI across multiple cohorts.
- The Czech cohort showed no clear associations between environmental changes and BMI, highlighting variability across regions.

## Abstract

Is moving to a different environment associated with body mass index (BMI) trajectories in young people through changes in the external exposome?

In this cohort study of 4359 children and young adults (aged 2-24 years) in the Netherlands, Sweden, and the Czech Republic with more than 30 000 age- and sex-standardized BMI (z-BMI) observations, moving to areas with higher environmental hazards (ie, more air pollution or less green space) was associated with increases in z-BMI, particularly in the Dutch cohort, with similar associations seen with gray space in the Swedish cohort; the Czech cohort showed no clear associations.

These findings suggest that greener, less polluted environments may help prevent unhealthy BMI trajectories in children and adolescents, with potential benefits differing across exposome domains and cohorts.

This cohort study investigates the associations of changes in the surrounding residential environment—specifically related to air pollution, the built environment, and socioeconomic disadvantage—with childhood body mass index trajectories.

Overweight and obesity affect millions of children and adolescents worldwide, and its prevalence is increasing.

To investigate the associations of changes in the surrounding residential environment following relocation on childhood body mass index (BMI), focusing on 3 external exposome domains: air pollution, the built environment, and socioeconomic disadvantage.

This longitudinal cohort study used harmonized data from birth cohorts from the Netherlands (PIAMA), Sweden (BAMSE), and the Czech Republic (ELSPAC-CZ) participating in the EXPANSE (Exposome Powered Tools for Healthy Living in Urban Settings) project, with birth dates ranging between 1991 and 1997. Participants were youths aged 2 to 24 years who had experienced residential relocation during their follow-up. Analysis focused on within-individual changes resulting from relocation. k Means clustering characterized multiple exposures from the 3 external exposome domains. Fixed-effects linear models estimated associations of exposome changes with changes in age- and sex-standardized body mass index (z-BMI), adjusted for relevant covariates. This study was conducted between July 2023 and January 2025.

Changes in 3 external exposome domains: (1) ambient air pollution from high-resolution surfaces; (2) the built environment, including green, blue, and gray spaces and light at night; and (3) area-level socioeconomic disadvantage indicators. Domain-specific exposome profiles were characterized as low-, medium-, and high-hazard environments.

Changes in z-BMI.

The study included 4359 participants (1467 from PIAMA, 1778 from BAMSE, and 1114 from ELSPAC-CZ). A total of 2215 (50.8%) were male. The mean (SD) age at inclusion was 3.0 (1.1) years, and mean (SD) age at moving was 7.7 (4.3) years. Parental education varied across cohorts. Mean (SD) z-BMI was 0.2 (1.1), 0.4 (1.0), and 0.1 (1.2) at baseline and 0.0 (1.0), 0.3 (1.0), and 0.1 (1.1) after moving in PIAMA, BAMSE, and ELSPAC-CZ, respectively. Moving to higher-hazard environments (more polluted, more gray space) was associated with increases in z-BMI for all domains in PIAMA; significant associations were also seen for some domains and exposures in BAMSE and ELSPAC-CZ. Specifically, an association between moving to a more built environment and increase in z-BMI was consistent across cohorts: an IQR increase in gray spaces was associated with increases of 0.04 (95% CI, 0.01-0.06) units and 0.05 (95% CI, 0.01-0.09) units in z-BMI in BAMSE and PIAMA, respectively. An IQR increase in air pollution hazard was associated with increases of 0.07 (95% CI, 0.02-0.12) units and 0.07 (95% CI, 0.01-0.14) units in z-BMI for nitrogen dioxide (NO2) and fine particulate matter (PM2.5), respectively, in PIAMA. Presence of effect modification by parental education and age at moving varied across cohorts.

In this multicountry cohort study of 4359 youths in the Netherlands, Sweden, and the Czech Republic, moving to greener, less urbanized environments was associated with healthy childhood BMI trajectories. Heterogeneity across cohorts highlighted the context-specific influence of external exposome domains on childhood weight.