What are the effects of air pollution on children’s health and development?
Summary of a HEN network member’s report
The current level of air pollution in Europe adversely affects children’s health. As a result of studies conducted around the world in recent decades, the knowledge and understanding of these effects have increased significantly. Reducing these effects is a priority of regional policies on health and the environment in the WHO European Region and is necessary for the achievement of the Millennium Development Goals on a global scale.
The review of accumulated evidence, published by WHO in 2005, considers the effects of air pollution in a number of areas. It considers the effects on the health and development of children during the prenatal period, on the development of the respiratory system and lung function (as well as respiratory morbidity), and on the incidence of childhood cancer. It also summarizes current knowledge about the links between air pollution and neurodevelopmental and behavioural effects.
The experts involved in preparing the report identified a hierarchy of health outcomes for which evidence: (a) is sufficient to infer a causal relationship with exposure to air pollution; (b) is suggestive of causality; or (c) is not sufficient or shows no association between outcomes and exposure.
Various periods of vulnerability characterize children. The intrauterine, perinatal and early childhood periods, during which the lungs are developing and maturing, are very vulnerable times. These are periods when the lungs are susceptible to injury by air pollutants. Exposure during these periods reduces the maximal functional capacity achieved in adult life and can lead to enhanced susceptibility during adulthood to infection and to the effects of such pollutants as tobacco smoke and those present in occupational exposures. Children with underlying chronic lung diseases, particularly asthma and cystic fibrosis, are especially vulnerable. These children are at greater risk of adverse effects from pollution than are healthy children. Also, children subject to higher exposures indoors – for example, from tobacco smoke or smoke from poorly maintained heating or cooking appliances – are at greater risk of being affected by outdoor pollutants.
Effects for which evidence is sufficient to infer a causal relationship with exposure to air pollution
There is now substantial evidence on the adverse effects of air pollution on different pregnancy outcomes and infant health. The evidence shows that air pollution, with concentrations typical of many European cities, increases the risk of death from respiratory causes in the postneonatal period.
The evidence also shows a relationship between exposure to ambient air pollutants and adverse effects on the development of lung function. Reversible lung function deficits, chronically reduced lung growth rates and lower lung function levels are associated with exposure to air pollution. Moreover, the evidence shows clearer relationships for particulate matter and traffic-related air pollution (indicated by nitrogen dioxide) than for other pollutants. Based on current knowledge, air pollutants seem to interact with other environmental factors, such as allergens, viruses and diet, that influence the overall impact of air pollutants on children’s health.
The report concludes that there is a causal relationship between exposure to air pollutants and aggravation of asthma. The evidence is also sufficient to assume a causal link between exposure to particulate matter and increased prevalence and incidence of cough and bronchitis.
In particular, such environmental contaminants as certain heavy metals and persistent organic pollutants show significant adverse effects on the development of the nervous system and behaviour in children. Also, there is sufficient evidence of a causal relationship between exposure to lead and neurobehavioral deficits in children, in terms of cognitive impairment.
Effects for which evidence is suggestive of causality
Studies on birth weight, preterm births and intrauterine growth retardation also suggest a link with air pollution, but these studies are still not sufficient to draw firm conclusions about the causality of the observed associations.
Although the report found little evidence for a causal link between the prevalence and incidence of asthma and air pollution in general, recent studies suggest that pollutants can enhance allergic sensitization in those genetically at risk, lending plausibility to the role of potentially injurious effects of ambient air pollutants in the causation of paediatric lung disease, including asthma. The mechanisms suggested for these effects need further research.
A significant body of evidence supports the view that much of the morbidity and mortality related to air pollution in children occurs via interactions with respiratory infections, which are very common among children. Evidence also suggests a causal relationship between exposure to ambient air pollution and increased incidence of upper and lower respiratory symptoms – many of them also being indicative of infections.
There is also evidence that suggests a causal link between adverse health effects and exposure to mercury, polychlorinated biphenyls and dioxins at current exposure levels.
Reduced exposure to air pollution seems to improve children’s health. As of yet, however, relatively few studies have looked at the effects of reduced air pollution. Nevertheless, existing studies show that reduced exposure to air pollutants can lead to a decrease in hospital admissions for respiratory complaints, a lower prevalence of bronchitis and respiratory infections, and improvement in lung function growth rates.
Effects for which evidence is not sufficient or shows no association between outcomes and exposure
Accumulated epidemiological evidence is insufficient to infer a causal link between childhood cancer and the levels of outdoor air pollution typically found in Europe. However, the number of studies available is limited, and their results are only partially consistent.
A reduction in children’s current exposure to air pollutants, especially from motor vehicle exhausts, is recommended. A decrease in motor vehicle exhausts will substantially benefit the respiratory health of children.
Further research is needed in the field of air quality to clarify the effect of specific air pollutants on children’s health, as well as the interaction of these pollutants with other environmental insults.
Type of evidence
This report is based on epidemiological and toxicological literature, published mainly during the last decade. Experts prepared synthesis papers, and these were reviewed externally and discussed according to a consensus assessment of the strength of the evidence on the links between various health outcomes and air pollution.
The views expressed in this summary are based on a publication of a HEN Network member agency and do not necessarily represent the decisions or stated policy of WHO/Europe.
This review was conducted within the scope of the project “Systematic review of health aspects of air pollution in Europe”, implemented by the WHO Regional Office for Europe.