Exposure to air pollution in utero, in infancy and in childhood affects BMI in childhood and early adolescence, with a stronger association demonstrated for boys than girls, according to a study published in the International Journal of Obesity.
“Most studies investigating the causes of childhood adiposity emphasize an imbalance between energy intake and expenditure ... while acknowledging that individual choices are influenced by environmental factors, such as availability and affordability of health food and neighborhood walkability,” Jian V. Huang, MPH, of the School of Public Health, Li Ka Shing Faculty of Medicine, University of Hong Kong, and colleagues wrote in the study background. “Less attention has been paid to the effects on childhood adiposity of traditional environmental factors, such as outdoor air quality, in terms of reduced physical activity, in response to warnings about low outdoor air quality or as a physiological response to air pollution.”
Researchers monitored 8,298 participants in a population-representative Chinese birth cohort who had been recruited in 1997 for a study on secondhand smoke exposure from postnatal visits at maternal and child health centers in Hong Kong. Researchers considered exposure to four air pollutants — particulate matter 10 µm (PM10), sulfur dioxide (SO2), nitric oxide (NO) and nitrogen dioxide (NO2) — during three growth periods: in utero, infancy (aged 0 to younger than 2 years) and childhood (aged 2 to younger than 8 years). To determine exposure, researchers calculated the mean of the weighted monthly air pollution concentrations from the three Environmental Protection Department monitoring stations closest to the mother’s residence. Researchers then calculated BMI at age 8 to younger than 10 years (median, 9.5 years), 10 to younger than 12 years (median, 11.5 years), 12 to younger than 14 years (median, 13.3 years) and 14 to younger than 16 years (median, 15.3 years).
Researchers found that mean BMI was 17.3 kg/m2, 18.8 kg/m2, 19.8 kg/m2 and 20.4 kg/m2 at 9.5, 11.5, 13.3 and 15.3 years, respectively. Between 4% and 5% of children had obesity at each age, defined as 2 standard deviations above the mean. Greater SO2 exposures in utero and in childhood were associated with lower BMI at age 13.3 and 15.3 years, and higher NO2 exposure in childhood was associated with higher BMI at all ages. Although exposure levels were similar for boys and girls, researchers found that associations between air pollution and BMI were more pronounced in boys.
These results point to the idea that air pollutants affect physiology, according to the researchers.
“Developing countries often suffer from high levels of air pollution and have rising levels of obesity,” the researchers wrote. “Exposure inequality between settings may aggravate health inequity and hinder economic development.” – by Melissa J. Webb
Disclosures: The study was funded by a grant from the Health Care and Promotion Fund, Health and Welfare Bureau, Government of the Hong Kong Special Administrative Region and by the Health and Health Services Research Fund. The authors report no other relevant financial disclosures.