A pregnant woman's exposure to tobacco smoke and pollution from road traffic can influence the development of behavioural outcomes in early childhood. This is the conclusion of a recent study led by a team from the Barcelona Institute for Global Health (ISGlobal), a centre supported by the "la Caixa" Foundation. The study, published in Environmental International, is the first to investigate the impact of the exposome--i.e. the set of all environmental exposures, both chemical and non-chemical, during the prenatal and postnatal stages--on child behaviour. Previous research had assessed the impact of environmental exposures separately but not as a whole.
Childhood is a critical time for people's mental health and well-being, as it is the period when brain development accelerates. Although the causes of behavioural problems are not yet well understood, we do know that the limited genetic component involved in behavioural disorders interacts with multiple social and physical exposures, particularly during the sensitive prenatal and early childhood periods.
The study was based on data from the large European Human Early-Life Exposome (HELIX) project. The study population consisted of six longitudinal birth cohorts from six European countries. A total of 1,287 children between 6 and 11 years of age underwent follow-up to characterise their exposures and assess behavioural problems. The researchers assessed 88 pregnancy exposures and 123 childhood exposures, encompassing the outdoor, indoor, chemical, lifestyle and social domains of the exposome.
Maternal Smoking and Road Traffic
During pregnancy, smoking and traffic were the factors most strongly associated with behavioural problems.
"We found that maternal tobacco smoke exposure during pregnancy was the most important prenatal exposure associated with emotional and behavioural problems in children," explained Léa Maitre, postdoctoral researcher at ISGlobal and lead author of the study. Maternal tobacco smoke exposure "is closely linked to other co-exposures, such as parental psychopathology symptoms, socioeconomic factors, the father's smoking habits and the home environment, in particular the quality of the attachment, support and stimulation that the child is exposed to at home," added Maitre. "This may account for a large part of the effect of maternal smoking during pregnancy on child behaviour."
The study also found that increased residential traffic density on the nearest road during pregnancy was associated with increased externalizing symptoms (i.e. aggressive and rule-breaking behaviours) and a higher attention deficit hyperactivity disorder (ADHD) index. A biological explanation is plausible, although the exact mechanisms remain elusive.
Postnatal exposure to tobacco smoke and car traffic density were not as strongly associated with child behaviour as prenatal exposures. This finding suggests that pregnancy may be the period most sensitive to the harmful effects of these exposures, due in part to the rapid development of the nervous system during this time window, but also because of exposures that occur in utero, among other hypotheses.
