BMI changes in adolescence mediate the effect of air pollution on metabolic health

Changes in Body Mass Index (BMI) during adolescence play an important role in the association between air pollution exposure and insulin resistance, according to a new study led by investigators from the Keck School of Medicine of USC.

The study, funded in part by the National Institute of Environmental Health Sciences and published in JAMA Network Open, found that children who were exposed to higher levels of traffic-related air pollution-specifically nitrogen oxides-tended to have a higher BMI by age 13, and experienced rapid weight gain from adolescence to young adulthood. This, in turn, was linked to higher levels of insulin resistance in their mid-20s.

We estimated about 42% of the relationship between early pollution exposure and insulin resistance can be explained by accelerated BMI growth trajectories-which describes how an individual's BMI changes over time-and further contributes to insulin resistance, a key risk factor for type 2 diabetes."

Fangqi Guo, PhD, MPH, postdoctoral scholar research associate, Department of Population and Public Health Sciences, Keck School of Medicine, and lead author of the study

"These findings held, even after accounting for other factors such as smoking, race/ethnicity, socioeconomic status, and parental history of diabetes," says Guo. "Our discovery is especially important for families and children living in high-traffic urban areas who may already face other socioeconomic or health disparities," says Guo.

Implications on metabolic health

With the rising incidence of type 2 diabetes and insulin resistance among young adults and children, the study's findings uncover how the harmful effects of air pollution may contribute to long-term metabolic problems.

In this study, the team of researchers specifically explored nitrogen oxides (NOx) emitted into the air from motor vehicles, categorized as traffic-related air pollution. (TRAP). TRAP exposure has been associated with a higher risk of developing type 2 diabetes, but the underlying mechanism of this association has not been fully understood. This study found that exposure to TRAP in childhood is associated with higher risk of insulin resistance in young adulthood, and the association may be partially explained by higher BMI and accelerated BMI growth from early adolescence into young adulthood.

The study included data from Meta-Air2, an ongoing substudy of the Southern California's Children's Health Study (CHS) and featured 282 participants enrolled in kindergarten or first grade in 2003, who were actively followed up until 2014. The study's researchers initiated a follow-up study in 2023 where participants, now young adults, provided blood samples for metabolic biomarker testing.

Informing public health interventions

"By identifying weight gain during adolescence as a key pathway between air pollution exposure and insulin resistance, our research underscores the importance of early interventions. These include promoting healthy lifestyle habits and weight management and improving air quality-in a bid to reduce the risk of chronic disease later in life," says Guo. "Public health efforts that address both environmental exposures and childhood obesity could make a significant impact."

About this study

In addition to Guo, the study's other authors are Xinci Chen, Steve Howland, Zhongzheng Niu, Lu Zhang, W. James Gauderman, Rob McConnell, MD, Theresa M. Bastain, Rima Habre, Carrie V. Breton, and Shohreh F. Farzan from the Department of Population and Public Health Sciences, Keck School of Medicine of USC, University of Southern California; Nathan Pavlovic and Fred Lurmann from Sonoma Technologies Inc, Petaluma, California.

This study was supported by grant R01ES031590 from the National Institute of Environmental Health Sciences; grant UH3OD023287 from the National Institutes of Health (NIH) Environmental Influences on Child Health Outcomes (ECHO) consortium; grants P01ES011627 and P30ES007048 from the NIEHS Southern California Environmental Sciences Center; grants P01ES022845, P2CES033433, and P01ES009581 from the Southern California Children's Environmental Health Center; and grants UL1TR001855 and UL1TR000130 from the National Center for Advancing Translational Sciences of the NIH.