Ambient air pollution and the development of overweight and obesity in children: a large longitudinal study

Background: Ambient air pollution may play a role in childhood obesity development, but evidence is scarce, and the modifying role of socioeconomic status (SES) is unclear. We aimed to examine the association between exposure to air pollution during early childhood and subsequent risk of developing overweight and obesity, and to evaluate whether SES is a modifier of this association. Methods: This longitudinal study included 416,955 children identified as normal weight between 2-5 years old and registered in an electronic primary healthcare record between 2006 and 2016 in Catalonia (Spain). Children were followed-up until they developed overweight or obesity, reached 15 years of age, died, transferred out, or end of study period (31/12/2018). Overweight and obesity were defined following the WHO reference obtained from height and weight measures. We estimated annual residential census levels of nitrogen dioxide (NO 2 ) and particulate matter <10 μm (PM 10 ), <2.5 μm (PM 2.5 ), and 2.5-10 μm (PM coarse ) at study entry. We estimated the risk of developing overweight and obesity per interquartile range increase in air pollution exposure with Cox proportional hazard models. Results: A total of 142,590 (34.2%) children developed overweight or obesity. Increased exposure to NO 2 , PM 10 , and PM coarse was associated with a 2-3% increased risk of developing overweight and obesity (hazard ratio [HR] per 21.8 μg/m 3 NO 2 = 1.03 [95% CI: 1.02-1.04]; HR per 6.4 μg/m 3 PM 10 = 1.02 [95% CI: 1.02-1.03]; HR per 4.6 µg/m 3 PM coarse = 1.02, [95% CI: 1.01-1.02]). For all air pollutants, associations were stronger among children living in most compared to least deprived areas. Conclusions: This study suggests that early life exposure to air pollution may be associated with a small increase in the risk of developing overweight and obesity in childhood, and that this association may be exacerbated in the most deprived areas. Even these small associations are of potential global health importance because air pollution exposure is widespread and the long-term health consequences of childhood obesity are clear.