Exposure to air pollution during pregnancy associated with reductions in children's lung function

New research by the Centre for Environmental Health and Sustainability (CESH) at the University of Leicester indicates that exposure to air pollution from road traffic as early as the first trimester of pregnancy and in early life is associated with small but significant reductions in children's lung function at the age of eight years. The research is being presented this week at the European Respiratory Congress in Madrid.

The research drew on data from the Avon Longitudinal Study of Parents and Children (ALSPAC), a long-term health study of 14,500 children born in the former county of Avon in 1991 and 1992, and their families. ALSPAC is the largest study to investigate the impact of particulate matter (PM₁₀) from different sources, including road traffic, on lung development and growth, and to analyze it by each trimester of pregnancy, as well as during infancy and childhood.

We found that exposure to road traffic PM₁₀in very early life showed harmful associations with lung function in eight-year-olds. Associations were stronger among boys, children whose mother had a lower education level or smoked during pregnancy. Our findings suggest that air pollution in pregnancy and early life has important impacts on lung function in early childhood; it may affect children's development and potentially also their long-term health trajectory."

Anna Hansell, professor in Environmental Epidemiology and Director of CESH

The researchers did not see similar associations between traffic pollution and lung function in children at the age of 15 years: "We think this may be because air pollution levels, particularly diesel emissions, were reducing over the time that the lung function was increasing in these analyses," said Professor Hansell. "However, it is also possible that the effect of air pollution is small and that lung growth is able to outpace the adverse effects by teenage years."

She said it was unclear how traffic pollution could affect childhood lung function, particularly during pregnancy. One mechanism could be that particles cross the placenta and disturb the development of the growing fetus's lungs through oxidative stress (an imbalance between free radical molecules and antioxidants). Another mechanism could be that prenatal exposure could induce epigenetic changes (changes in gene function that do not involve changes in DNA sequences).

Professor Hansell concluded:

It's really important to prioritize reduction of air pollution levels to improve respiratory health. In separate work, we have also shown associations with lower lung function in adulthood, suggesting that air pollution contributes to the aging of the lungs. Lung health is a marker of general health and associated with numerous other chronic diseases."

Methodology

Between 1990 and 2008, researchers calculated exposures to PM₁₀in 13,963 children for each trimester, and at the ages of 0-6 months, 7-12 months and then annually to the age of 15 years. They measured the volume of air that the children could force out in one second (FEV1) and the maximum amount of air they could forcibly exhale after taking the deepest possible breath (FVC) at the age of eight and 15 years. The results were adjusted for age, gender and height.

Results

The average amount of PM₁₀derived from road traffic that the children were exposed to was one microgram per cubic metre of air (mcg/m3), but exposure varied from zero to eight mcg/m³over the periods measured. Every 1 mcg/m³increase above zero in exposure to PM₁₀from traffic during the first trimester was associated with a 0.8% reduction in lung function. This corresponds to an average reduction in FEV1 and FVC lung function of 14 and 16 milliliters, respectively, by the age of eight years. The researchers found similar associations for exposure to traffic PM₁₀during the second and third trimesters, over the whole pregnancy, and up to the age of eight. Exposure to PM₁₀from all sources during the third trimester was significantly associated with reduced lung function.