EFFECT OF EARLY LIFE EXPOSURE TO AIR POLLUTION ON DEVELOPMENT OF CHILDHOOD ASTHMA

EFFECT OF EARLY LIFE EXPOSURE TO AIR POLLUTION ON THE DEVELOPMENT OF CHILDHOOD ASTHMA

CHAPTER ONE

INTRODUCTION

• Background of the study

 Asthma is a chronic inflammatory disease of the airway which has a large impact on quality of life and poses a great burden on health services. In children, asthma is the most commonly reported chronic disease in developed countries.  Environmental factors, importantly including improved hygiene, ambient air pollution exposures, and early-life exposures to microbes and aeroallergens, contribute to the development of asthma. In a recent systematic review and meta-analyses, we found statistically significant associations between traffic-related air pollution (TRAP) and the incidence and lifetime prevalence of childhood asthma, although there was significant heterogeneity in some of the risk estimates. These effects are biologically plausible. Britain’s Committee on the Medical Effects of Air Pollutants proposed four mechanisms by which air pollution can affect asthma; oxidative stress and damage; inflamed pathways; airway remodeling; and enhancement of respiratory sensitization to allergens. Oxidative stress relates to common asthmatic traits, and was suggested to play a role in asthma pathogenesis. Further, it was previously highlighted as one chief pathway which underpins the adverse health effects of (traffic-related) air pollution on the respiratory systems. TRAP is a particularly important and challenging exposure to study given its ubiquity, its dominance in present urban areas, its proximity to human receptors, and its high spatial and temporal variability. Concerns about children’s health and the factors that affect it are important determinants of health policies. In particular, policies that aim to prevent the adverse effects of environmental factors on health consider children as the population group that deserves the highest level of protection. High-level international policy documents, such as the declarations of the Ministerial Conferences on Environment and Health convened in London in 1999 and Budapest in 2004, highlight this concern. The Budapest Conference also adopted the Children’s Environment and Health Action Plan for Europe, which formulates actions aiming to prevent and reduce the burden of environment-related diseases in children in the WHO European Member States. Reduction of the adverse effects of air pollution on children’s health, and in particular on the occurrence of respiratory disease, is one of the four regional priority goals of the Action Plan. The most effective policy actions are those based on well-established evidence of the links between children’s health and environmental exposures, ensuring that the prevention of exposure leads to improved health. As a result of studies conducted around the world in recent decades, knowledge and understanding of the risks of air pollution to children is growing. Nevertheless, the available studies are not always consistent in terms of the health outcomes and exposures assessed, and employ a wide range of analyses and reporting methods. Recent studies have tended to be more sophisticated and to consider in more detail the complexity of children’s exposure to environmental factors, changes in the physiology of the developing organism, and morbidity characteristic for the age of the child. The synthesis of accumulated evidence thus requires it to be thoroughly and systematically analyzed, looking for logical links between studies that point to causal associations between exposures and health effects. Such synthesis furnishes the most solid policy basis and allows one to focus on the relevant exposures and to effectively reduce the burden of disease due to these exposures. The Air quality guidelines for Europe, first published by WHO in 1987 and updated at the end of the 1990s, provide a comprehensive assessment of the hazards of air pollution to all population groups, including children. Several new studies carried out over the last few years, however, potentially provide new insight into the evidence, employ new study methods, and address exposure to pollution mixes and levels now characteristic of European cities.

EFFECT OF EARLY LIFE EXPOSURE TO AIR POLLUTION ON THE DEVELOPMENT OF CHILDHOOD ASTHMA