Could air pollution be making us fat?

A new USC study suggests that exposure to traffic pollution during childhood makes adolescents 34 percent more likely to eat foods high in unhealthy trans fats — regardless of household income, parent education level or proximity to fast-food restaurants. The findings on air pollution and obesity in teens appear in The American Journal of Clinical Nutrition.

“Strange as it may seem, we discovered kids in polluted communities ate more fast food than other kids,” said Zhanghua Chen, PhD, a postdoctoral research associate in the Department of Population and Public Health Sciences at the Keck School of Medicine of USC, and the study’s first author.

The link is not as far-fetched as it might appear. The researchers cited a 2012 study in mice that found in-utero exposure to diesel exhaust resulted in mice consuming 14 percent more calories than the offspring of pregnant mice exposed to filtered air.

The exact mechanisms linking air pollution and obesity aren’t known, but researchers hypothesize that oxidative stress and inflammation may be to blame. In the mouse study, prenatal exhaust exposure was paralleled by changes in neuroinflammation and structure in parts of the brain involved in food-seeking and dietary decision-making behavior.

A USC study found that exposure to traffic pollution during childhood makes adolescents more likely to eat foods high in unhealthy trans fats. (Photo/iStock)

Air pollution and obesity in teens: Tracking 3,100 kids

For the current study, researchers used data from 3,100 school-age children who were enrolled in the USC Children’s Health Study during 1993-1994 and followed for four to eight years. The USC Children’s Health Study, which began in 1992 and is ongoing, is one of the largest and most detailed studies of the long-term effects of air pollution on the respiratory health of children. Eight of the USA’s 10 most-polluted metropolitan areas, in terms of ozone pollution, are in California, according to the American Lung Association’s annual “State of the Air” report for 2018.

Researchers collected yearly diet information with a 131-item questionnaire that asked participants how frequently they consumed certain foods, from less than once per month to two or more servings per day. Participants also reported how often they ate dinner prepared away from home.

Pollutants such as nitrogen dioxide, which comes from traffic and power plant emissions, were measured at central monitoring stations, and concentrations were estimated for participants’ residential addresses.

Researchers took into account — and used statistical methods to remove — factors such as parental education level, household income of each child participant, the number of fast-food restaurants within a 500-meter buffer zone near school and home, community-level poverty rates and low education rates.

Correlation between air pollution and obesity in teens

Even after that adjustment, the correlation remained strong between childhood exposures to air pollution and increased consumption by adolescents of trans fat and fast foods.

“Given how rapidly the brain matures throughout childhood and adolescence, it’s a time frame when environmental factors could have potentially long-lasting effects on brain and behavior,” said Chen. “We plan to conduct more studies to investigate the role of air pollutant exposures in changes of brain function, dietary behavior and obesity onset in the future.”

The percentage of children and adolescents in the United States affected by obesity has more than tripled since the 1970s, according to the U.S. Centers for Disease Control and Prevention. Data from 2015-2016 show that nearly 1 in 5 school-age children and young people (6 to 19 years) in the country are obese. Obesity increases risk for asthma, diabetes, bone and joint problems, cancer and heart disease.

In addition to Chen, the study’s authors are Frank Gilliland (senior author and principal investigator of the Children’s Health Study), Megan Herting, Leda Chatzi, Britni Belcher and Rob McConnell, all of USC; and Tanya Alderete of the University of Colorado Boulder.

The research was supported by Southern California Environmental Health Sciences Center grant 5P30ES007048 funded by the National Institute of Environmental Health Sciences; National Institute of Environmental Health Sciences supported grants 5P01ES011627, K99ES027870, and K99ES027853; Southern California Children’s Environmental Health Center grants funded by the National Institute of Environmental Health Sciences (5P01ES022845-03); the U.S. Environmental Protection Agency (RD83544101); the University of Southern California’s Diabetes and Obesity Research Institute Pilot Project; the Southern California Clinical and Translational Science Institute Pilot Funding Program grant UL1TR001855; and the Hastings Foundation.

— Leigh Hopper