The association of air pollution with body mass index: evidence from Hong Kong's "Children of 1997" birth cohort.

BACKGROUND: Child overweight and obesity have increased substantially in many countries. Physical and psychological effects of childhood obesity endure throughout adulthood. Much attention has been paid to energy intake and expenditure in childhood adiposity, but less to environmental factors, such as outdoor air quality. Here we assessed prospectively the association of exposure to air pollution with body mass index (BMI) in late childhood and early adolescence.

METHODS: We assessed the association of air pollutants (particulate matter with a diameter of 10 µm or less (PM10 ), sulfur dioxide (SO2 ), nitric oxide (NO), and nitrogen dioxide (NO2 )) at different growth phases (in utero, in infancy, and in childhood) with BMI at ~9, ~11, ~13, and ~15 years in a population-representative birth cohort from Hong Kong, "Children of 1997." We used partial least square regression to account for colinearity between pollutants and exposure periods. We also assessed whether associations varied by sex from model fit.

RESULTS: Associations were sex-specific based on better model fit when including sex interaction terms. Among boys, higher SO2 in utero was associated with lower BMI at ~13 and ~15 years, higher SO2 in childhood with lower BMI at ~15 years, and higher NO2 in childhood with higher BMI at ~9, ~13, and ~15 years using a multi-pollutant model.

CONCLUSIONS: These findings of air pollutant- and sex-specific associations with adiposity should give impetus to the investigation of their physiological effects, possibly operating as endocrine disruptors or via mitochondria, so as to protect the next generation of boys.