Weight Trajectories Among Youths Following Residential Relocation

Introduction

Overweight and obesity are serious global public health challenges that affect millions of children and adolescents worldwide. The prevalence of childhood obesity has been rising steadily, increasing risks for metabolic and cardiovascular diseases later in life. Understanding environmental factors that influence weight gain during childhood and adolescence is critical to developing effective prevention strategies.

This study investigates how changes in residential environments following relocation relate to body mass index (BMI) trajectories in youths. We focus on three main external exposome domains: ambient air pollution, the built environment (including green spaces, water bodies, urban gray spaces, and nighttime light), and socioeconomic disadvantage at the area level. The exposome concept reflects the totality of environmental exposures an individual experiences throughout life, which may shape health outcomes such as obesity.

Study Design and Participants

This longitudinal cohort study compiled harmonized data from three European birth cohorts: PIAMA from the Netherlands, BAMSE from Sweden, and ELSPAC-CZ from the Czech Republic. The cohorts included children born between 1991 and 1997, followed up from infancy into young adulthood (ages 2 to 24 years).

Participants were selected based on having experienced residential relocation during their follow-up period, allowing analysis of within-individual changes in environmental exposures and subsequent BMI changes. A total of 4359 youths were included, with a nearly equal gender distribution. Parental education levels, a key socioeconomic indicator, varied across cohorts and were considered in the analyses.

Exposure Assessment

Environmental exposures were categorized into three domains:

1. Ambient Air Pollution – High-resolution data were used to assess exposure to pollutants such as nitrogen dioxide (NO2) and fine particulate matter (PM2.5).

2. Built Environment – Measures included the proportion of green space (parks, forests), blue space (lakes, rivers), and gray space (urban built-up areas lacking vegetation), as well as levels of nighttime artificial light.

3. Socioeconomic Disadvantage – Area-level indicators such as income, education, and employment rates were used to characterize socioeconomic status of neighborhoods.

Using k-means clustering, profiles of local environmental hazards were identified to classify each domain into low-, medium-, and high-hazard categories.

Outcomes and Statistical Analysis

The primary outcome was changes in age- and sex-standardized BMI scores (z-BMI) following relocation. Fixed-effects linear regression models estimated associations between changes in exposome profiles and z-BMI, controlling for potential confounders including parental education and age at moving. The modeling approach focused on within-individual changes, thereby reducing confounding from time-invariant personal characteristics.

Results

The average age at the time of joining the study was 3 years, with relocation occurring on average at 7.7 years. Across cohorts, mean z-BMI values showed slight decreases or stability after moving.

Importantly, moving to environments classified as higher hazard—characterized by increased air pollution and more extensive gray urban space—was significantly associated with increases in z-BMI, particularly in the PIAMA cohort. Similar associations were identified in BAMSE and ELSPAC-CZ, though with some variability.

For example, an interquartile range (IQR) increase in gray space was linked to z-BMI increases of 0.04 to 0.05 units in BAMSE and PIAMA, respectively. Likewise, in PIAMA, an IQR increase in NO2 and PM2.5 exposure correlated with z-BMI increases of approximately 0.07 units.

Conversely, relocating to greener, less urbanized areas was associated with healthier BMI trajectories, demonstrating protective effects of natural environments on childhood weight.

The influence of parental education and age at moving on these associations varied across cohorts, pointing to context-specific factors in how environmental changes impact childhood obesity risk.

Discussion

This multicountry study highlights the complex relationships between environmental exposures and childhood weight outcomes. Exposure to higher air pollution levels and urban gray spaces may promote unhealthy weight gain, possibly via mechanisms like reduced physical activity opportunities, increased stress, or pollutant-related metabolic changes.

The protective association of greenspaces aligns with evidence that access to natural environments encourages physical activity, improves mental health, and reduces obesity risk.

Variability in findings across cohorts emphasizes that local social and environmental contexts modulate how relocation affects children’s BMI. Parental education modified associations, suggesting that family-level factors can influence vulnerability or resilience to environmental risks.

Implications for Public Health and Urban Planning

These findings support policies promoting greener and less polluted residential neighborhoods to improve childhood health trajectories. Urban planning strategies increasing green and blue spaces, reducing gray urban sprawl, and lowering air pollution exposure could have a meaningful impact on reducing childhood obesity prevalence.

Consideration of socioeconomic context remains vital to address disparities and ensure equitable access to healthy environments.

Limitations

The study used observational data; causal inference warrants caution. Residual confounding by unmeasured factors cannot be excluded. Additionally, cohort-specific contexts limit direct generalizability to other regions.

However, the longitudinal within-individual design strengthens causal interpretation compared to cross-sectional studies.

Conclusions

Relocation to greener and less polluted environments correlates with healthier childhood BMI trajectories across multiple European cohorts, while moving to more hazardous urban areas associates with weight gain.

These findings underscore the importance of supportive residential environments for healthy growth and the need for integrated approaches considering environmental and socioeconomic dimensions in preventing childhood obesity.