“Stressed-out mums and dads could be to blame for the epidemic in childhood asthma,” the Daily Mirror reported. It said a study of almost 2,500 healthy children over three years found that those exposed to more air pollution were more likely to develop asthma, and that parental stress increased this risk even more.
This study suggests that socioeconomic status and parental stress may increase the risks associated with traffic-related pollution and maternal smoking on pregnancy although by themselves they do not appear to affect asthma risk.
The study does have some limitations, including the fact that socioeconomic status was based only on the level of parental education, parental stress was only measured at one time point and that many of the factors assessed including children’s diagnoses, were based on reports from the parents only and not independently verified. Further studies will need to confirm these results.
The research was carried out by Dr Ketan Shankardass and colleagues from the Li Ka Shing Knowledge Institute of St Michael’s Hospital, Canada and two US universities. It was funded by the National Institute of Environmental Health Sciences, the US Environmental Protection, a National Cancer Institute Grant, the Hastings Foundation, and the Canadian Institutes of Health Research.
The study was published in the peer-reviewed scientific journal, Proceedings of the National Academy of Sciences of the United States of America .
This research is part of a prospective cohort study called the Southern Californian Children’s Health Study. The study has already shown that traffic-related pollution and maternal smoking during pregnancy were associated with an increased risk of asthma in children. The current analyses aimed to look at whether socioeconomic status and parental stress might increase the risk of asthma even further in children exposed to pollution and maternal smoking.
The researchers enrolled children between five and nine years of age, who were attending schools in 13 communities in southern California in 2002 and 2003. All students from the study communities were asked to participate and 65% (5,349 children) returned the study questionnaires given. These questionnaires asked about the children’s health, including questions about chest-related conditions and allergies. They also asked about other factors such as race, gender, where they lived, type of medical insurance coverage, whether they had been exposed to maternal smoking during pregnancy or if anyone in the home currently smoked on a daily basis, and family history of asthma. Each household’s exposure to traffic-related pollution was estimate, based on their location and distance from local ‘measured’ sources of pollutants, such as traffic.
Parental education was used as a measure of the family’s socioeconomic status. Parental stress levels were measured at the start of the study using a standard question (the Parental Stress Scale, PSS):
“In the last month, how often have you felt:
The parents rated how often they felt each of these on a scale of zero to four, and the scores were summed to give a score from zero to 16 (higher scores indicating greater stress).
The children’s living conditions were assessed using questions about: type of home; whether the child lived elsewhere for more than 50 days a year; previous water damage or flooding in the home; the presence of mould or mildew on household surfaces, the presence of a musty smell and cockroaches or pets in the home. There were also questions about whether gas stoves, air conditioners, humidifiers or vaporisers were used in the home and whether the child’s bedroom had a carpet.
The researchers excluded children who had already been diagnosed with asthma those who had wheezing episodes, and those who did answer or know. Children whose exposure to traffic-related pollution could not be assessed, and those who were lost to the follow up carried out in the first year of the study were also excluded. This left 2,497 children for analysis. Just over half of the children (55%) were Hispanic, just over a third non-Hispanic white (36%), 3% African American, and 6% of other races or ethnic groups.
During the three years of follow up, the children’s parents filled out annual questionnaires about the children’s health, including whether they had been diagnosed with asthma. The researchers looked at how the factors assessed affected a child’s risk of developing asthma during the follow up. In particular, they looked at the effects of traffic-related pollution and maternal smoking during pregnancy, and whether parental stress or socioeconomic stress affected the level of risk associated with these factors. They took into account the factors that they measured that could affect outcome in their analyses, such as age, gender, and ethnicity.
About 21% of families were defined as being of low socioeconomic status because the parents had not finished high school. On average, parental stress score was 3.85 on the PSS (the most stressed score possible was 16).
Just under 5% of children (120 children) developed asthma during the follow up. African American children were more likely than Hispanic children to develop asthma. Children who were underweight, had a history of chest illness or allergy, who lived in a home with a musty smell or whose parents had asthma were also more likely to develop asthma.
Low socioeconomic status and higher parental stress alone did not increase the risk of developing asthma.
Increasing exposure to traffic-related pollution did increase the risk of childhood asthma. Among children in low socioeconomic status families or those with parents with higher levels of stress, the effects of traffic-related pollution were greater than in children from high socioeconomic status families or parents with lower levels of stress. The effects of socioeconomic status were reduced if parental stress was taken into account.
Exposure to maternal smoking during pregnancy did not significantly increase the risk of childhood asthma overall. However, exposure to maternal smoking during pregnancy did significantly increase risk of childhood asthma in children from low socioeconomic status families or those with parents with higher levels of stress.
The researchers conclude that, “children whose parents perceived their lives as unpredictable, uncontrollable, or overwhelming had increased risk of new onset asthma associated with [traffic-related pollution] and maternal smoking during pregnancy”. They also say, “understanding the role of air pollution in the causation of complex diseases like asthma requires consideration of how social factors may modify the effects of environmental exposures”.
This study suggests that socioeconomic status and parental stress may exacerbate the risks associated with traffic related pollution and maternal smoking on pregnancy, although by themselves they do not appear to affect asthma risk. It has the advantage of having collected the data over time (prospectively), however, there are some limitations to note:
Further studies will be needed to confirm these results.