The role of outdoor air pollution and climatic changes on the rising trends in respiratory allergy.

Evidence suggests that allergic respiratory diseases such as hay fever and bronchial asthma have become more common world-wide in the last two decades, and the reasons for this increase are still largely unknown. A major responsible factor could be outdoor air pollution, derived from cars and other vehicles. Studies have demonstrated that urbanization and high levels of vehicle emissions and westernized lifestyle is correlated with the increasing frequency of pollen-induced respiratory allergy. People who live in urban areas tend to be more affected by pollen-induced respiratory allergy than those from of rural areas. Pollen allergy has been one of the most frequent models used to study the interrelationship between air pollution and respiratory allergic diseases. Pollen grains or plant-derived paucimicronic components carry allergens that can produce allergic symptoms. They may also interact with air pollution (particulate matter, ozone) in producing these effects. There is evidence that air pollutants may promote airway sensitization by modulating the allergenicity of airborne allergens. Furthermore, airway mucosal damage and impaired mucociliary clearance induced by air pollution may facilitate the access of inhaled allergens to the cells of the immune system. In addition, vegetation reacts with air pollution and environmental conditions and influence the plant allergenicity. Several factors influence this interaction, including type of air pollutants, plant species, nutrient balance, climatic factors, degree of airway sensitization and hyperresponsiveness of exposed subjects.     

Effects of climatic changes and urban air pollution on the rising trends of respiratory allergy and asthma

ABSTRACT: Over the past two decades there has been increasing interest in studies regarding effects on human health of climate changes and urban air pollution. Climate change induced by anthropogenic warming of the earth's atmosphere is a daunting problem and there are several observations about the role of urbanization, with its high levels of vehicle emissions and other pollutants, and westernized lifestyle with respect to the rising frequency of respiratory allergic diseases observed in most industrialized countries.There is also evidence that asthmatic subjects are at increased risk of developing exacerbations of bronchial obstruction with exposure to gaseous (ozone, nitrogen dioxide, sulfur dioxide) and particulate inhalable components of air pollution.A change in the genetic predisposition is an unlikely cause of the increasing frequency in allergic diseases because genetic changes in a population require several generations. Consequently, environmental factors such as climate change and indoor and outdoor air pollution may contribute to explain the increasing frequency of respiratory allergy and asthma. Since concentrations of airborne allergens and air pollutants are frequently increased contemporaneously, an enhanced IgE-mediated response to aeroallergens and enhanced airway inflammation could account for the increasing frequency of allergic respiratory diseases and bronchial asthma.Scientific societies such as the European Academy of Allergy and Clinical Immunology, European Respiratory Society and the World Allergy Organization have set up committees and task forces to produce documents to focalize attention on this topic, calling for prevention measures.     

Outdoor air pollution, climatic changes and allergic bronchial asthma.

Both the prevalence and severity of respiratory allergic diseases such as bronchial asthma have increased in recent years. Among the factors implicated in this "epidemic" are indoor and outdoor airborne pollutants. Urbanisation with its high levels of vehicle emissions and Westernised lifestyle parallels the increase in respiratory allergy in most industrialised countries, and people who live in urban areas tend to be more affected by the disease than those of rural areas. In atopic subjects, exposure to air pollution increases airway responsiveness to aeroallergens. Pollen is a good model with which to study the interrelationship between air pollution and respiratory allergic diseases. Biological aerosols carrying antigenic proteins, such as pollen grains or plant-derived paucimicronic components, can produce allergic symptoms. By adhering to the surface of these airborne allergenic agents, air pollutants could modify their antigenic properties. Several factors influence this interaction, i.e., type of air pollutant, plant species, nutrient balance, climatic factors, degree of airway sensitisation and hyperresponsiveness of exposed subjects. However, the airway mucosal damage and the impaired mucociliary clearance induced by air pollution may facilitate the penetration and the access of inhaled allergens to the cells of the immune system, and so promote airway sensitisation. As a consequence, an enhanced immunoglobulin E-mediated response to aeroallergens and enhanced airway inflammation favoured by air pollution could account for the increasing prevalence of allergic respiratory diseases in urban areas.     

Environmental exposure to air pollution and allergens and peak flow changes.

Laboratory-based studies have shown that ozone and nitrogen dioxide can potentiate the effect of allergen in sensitized asthmatic subjects, but it is not known whether this interaction is important under natural exposure conditions. Thirty-five subjects with clinical diagnoses of asthma or chronic obstructive pulmonary disease and with a provocative dose causing a 20% fall in forced expiratory volume in one second methacholine <12.25 micromol (using the Yan method) kept peak expiratory flow (PEF) records for a 4-week period during late summer, with concurrent measurement of spore and pollen counts and pollution levels. Multiple regression analysis was then used to determine the effect on PEF of aeroallergen, and of the interaction between aeroallergen and pollutant levels. A statistically significant interaction was demonstrated between total spore count and ozone, but not nitrogen dioxide. Mean PEF fell in association with increasing spore count (same-day and 24-h lag level) and PEF variability increased with increasing spore count (24-h lag level only); both changes were greater the higher the prior ozone level. These results suggest that ozone can potentiate the effect of aeroallergens in subjects with bronchial hyperreactivity under natural exposure conditions. However, the effect was small, and the clinical significance of the interaction requires further study.     

Short-term associations between outdoor air pollution and visits to accident and emergency departments in London for respiratory complaints.

Many epidemiological studies have shown positive short-term associations between health and current levels of outdoor air pollution. The aim of this study was to investigate the association between air pollution and the number of visits to accident and emergency (A&E) departments in London for respiratory complaints. A&E visits include the less severe cases of acute respiratory disease and are unrestricted by bed availability. Daily counts of visits to 12 London A&E departments for asthma, other respiratory complaints, and both combined for a number of age groups were constructed from manual registers of visits for the period 1992-1994. A Poisson regression allowing for seasonal patterns, meteorological conditions and influenza epidemics was used to assess the associations between the number of visits and six pollutants: nitrogen dioxide, ozone, sulphur dioxide, carbon monoxide, and particles measured as black smoke (BS) and particles with a median aerodynamic diameter of <10 microm (PM10). After making an allowance for the multiplicity of tests, there remained strong associations between visits for all respiratory complaints and increases in SO2: a 2.8% (95% confidence interval (CI) 0.7-4.9) increase in the number of visits for a 18 microg x (-3) increase (10th-90th percentile range) and a 3.0% (95% CI 0.8-5.2) increase for a 31 microg x m(-3) increase in PM10. There were also significant associations between visits for asthma and SO2, NO2 and PM10. No significant associations between O3 and any of the respiratory complaints investigated were found. Because of the strong correlation between pollutants, it was difficult to identify a single pollutant responsible for the associations found in the analyses. This study suggests that the levels of air pollution currently experienced in London are linked to short-term increases in the number of people visiting accident and emergency departments with respiratory complaints.     

The effect of air pollution on asthma and allergy

Air pollution exposure is associated with increased asthma and allergy morbidity and is a suspected contributor to the increasing prevalence of allergic conditions. Observational studies continue to strengthen the association between air pollution and allergic respiratory disease, whereas recent mechanistic studies have defined the prominent role of oxidative stress in the proallergic immunologic effects of particulate and gaseous pollutants. The identification of common genetic polymorphisms in key cytoprotective responses to oxidative stress has highlighted the importance of individual host susceptibility to pollutant-induced inflammation. Future therapy to reduce the adverse effects of air pollution on allergic respiratory disease will likely depend on targeting susceptible populations for treatment that reduces oxidative stress, potentially through enhancement of phase 2 enzymes or other antioxidant defenses.     

Mechanistic impact of outdoor air pollution on asthma and allergic diseases

Over the past decades, asthma and allergic diseases, such as allergic rhinitis and eczema, have become increasingly common, but the reason for this increased prevalence is still unclear. It has become apparent that genetic variation alone is not sufficient to account for the observed changes; rather, the changing environment, together with alterations in lifestyle and eating habits, are likely to have driven the increase in prevalence, and in some cases, severity of disease. This is particularly highlighted by recent awareness of, and concern about, the exposure to ubiquitous environmental pollutants, including chemicals with oxidant-generating capacities, and their impact on the human respiratory and immune systems. Indeed, several epidemiological studies have identified a variety of risk factors, including ambient pollutant gases and airborne particles, for the prevalence and the exacerbation of allergic diseases. However, the responsible pollutants remain unclear and the causal relationship has not been established. Recent studies of cellular and animal models have suggested several plausible mechanisms, with the most consistent observation being the direct effects of particle components on the generation of reactive oxygen species (ROS) and the resultant oxidative stress and inflammatory responses. This review attempts to highlight the experimental findings, with particular emphasis on several major mechanistic events initiated by exposure to particulate matters (PMs) in the exposure-disease relationship.     

Effects of air pollution on the respiratory tract of children.

The effects of air pollution on pulmonary function and respiratory status was evaluated in 1,626 school aged children from a European Alpine region. Based on measurements of SO₂, NO₂ and O₃ as well as infrared imaging and lichen mapping, three zones of exposure were defined. Results of standardized respiratory questionnaires, medical examinations, and lung function tests were compared among the children in the three different exposure zones. After controlling for age, sex, height, socioeconomic status, and exposure to environmental tobacco smoking, areas of increased SO₂ and NO₂ as well as areas of increased ozone (max. half hourly mean value, 146 ppb) were significantly associated with decrements of forced expiratory volume in 1 s (FEV₁) and flow rates at 50 and 75% of vital capacity (FEF₅₀ FEF₇₅). In addition, areas with increased ozone had a higher prevalence of asthma In all regions, maternal smoking was associated with reduced expiratory flow rates and increased prevalence of asthma. The results provide evidence that outdoor pollution and exposure to passive smoking are risk factors for childhood respiratory health. © 1993 Wiley-Liss, Inc.     

Inner city air pollution and respiratory health and atopy in children.

The impact of inner city air pollution on the development of respiratory and atopic diseases in childhood is still unclear. In a cross sectional study in Dresden, Germany, 5,421 children in two age groups (5-7 yrs and 9-11 yrs) were studied according to the International Study of Asthma and Allergies in Childhood (ISAAC) phase II protocol. The prevalences of wheezing and cough as well as doctor diagnosed asthma and bronchitis were assessed by parental questionnaires. Children also underwent skin-prick testing, venipuncture for the measurement of serum immunoglobulin (Ig)E, lung function testing and a bronchial challenge test (4.5% saline) to assess airway hyperresponsiveness. Exposure was assessed on an individual basis by relating mean annual air pollution levels (SO2, NO2, CO, benzene, and O3) which had been measured on a 1 km2 grid, to the home and school address of each study subject. After adjusting for potential confounding factors an increase in the exposure to benzene of 1 microg x m3 air was associated with an increased prevalence of morning cough (adjusted odds ratio (aOR)): 1.15; 1.04-1.27) and bronchitis (aOR: 1.11; 1.03-1.19). Similar associations were observed for NO2 and CO. In turn, the prevalences of atopic sensitization, symptoms of atopic diseases and bronchial hyperresponsiveness were not positively associated with exposure to any of these pollutants. It is concluded that in this study a moderate increase in exposure to traffic-related air pollution was associated with an increased prevalence of cough and bronchitis, but not with atopic conditions in children.     

The effects of outdoor air pollution on the respiratory health of Canadian children: A systematic review of epidemiological studies

BACKGROUND:

Outdoor air pollution is a global problem with serious effects on human health, and children are considered to be highly susceptible to the effects of air pollution.

OBJECTIVE:

To conduct a comprehensive and updated systematic review of the literature reporting the effects of outdoor air pollution on the respiratory health of children in Canada.

METHODS:

Searches of four electronic databases between January 2004 and November 2014 were conducted to identify epidemiological studies evaluating the effect of exposure to outdoor air pollutants on respiratory symptoms, lung function measurements and the use of health services due to respiratory conditions in Canadian children. The selection process and quality assessment, using the Newcastle-Ottawa Scale, were conducted independently by two reviewers.

RESULTS:

Twenty-seven studies that were heterogeneous with regard to study design, population, respiratory outcome and air pollution exposure were identified. Overall, the included studies reported adverse effects of outdoor air pollution at concentrations that were below Canadian and United States standards. Heterogeneous effects of air pollutants were reported according to city, sex, socioeconomic status and seasonality. The present review also describes trends in research related to the effect of air pollution on Canadian children over the past 25 years.

CONCLUSION:

The present study reconfirms the adverse effects of outdoor air pollution on the respiratory health of children in Canada. It will help researchers, clinicians and environmental health authorities identify the available evidence of the adverse effect of outdoor air pollution, research gaps and the limitations for further research.     

Obesity and air pollution: global risk factors for pediatric non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) is becoming as an important health problem in the pediatric age group. In addition to the well-documented role of obesity on the fatty changes in liver, there is a growing body of evidence about the role of environmental factors, such as smoking and air pollution, in NAFLD. Given that excess body fat and exposure to air pollutants is accompanied by systemic low-grade inflammation, oxidative stress, as well as alterations in insulin/insulin-like growth factor and insulin resistance, all of which are etiological factors related to NAFLD, an escalating trend in the incidence of pediatric NAFLD can be expected in the near future. This review focuses on the current knowledge regarding the epidemiology, diagnosis and pathogenesis of pediatric NAFLD. The review also highlights the importance of studying the underlying mechanisms of pediatric NAFLD and the need for broadening efforts in prevention and control of the main risk factors. The two main universal risk factors for N LD, obesity and air pollution, have broad adverse health effects, and reducing their prevalence will help abate the serious health problems associated with pediatric NAFLD.     

Environmental factors and asthma and allergy in schoolchildren from Western Australia.

The association of environmental factors with atopic disease in children remains poorly understood. The aim of this study was to investigate the relationship between socio-environmental factors and symptoms of asthma and atopy in 6-7-yr-old children assessed as an adjunct to Phase I of the International Study of Asthma and Allergy in Childhood in Perth, Western Australia. Parental questionnaire responses were obtained for 2,193 children (73.6%) in 34 randomly selected primary schools in the Perth metropolitan area. Children born in Australia had a significantly increased risk of current asthma (odds ratio (OR) 237, p = 0.001). Having a mother born in Australia was the only factor independently associated with an increased risk of current hay fever (OR 1.56, p = 0.005). Increasing numbers of people living in the home were significantly associated with a multiplicative decrease in risk of current asthma (OR 0.88, p = 0.03) and eczema (OR 0.82, p = 0.01). Houses made of fibrocement (OR 2.40, p = 0.02) and the presence of mats on less than half of the floor area in the "main bedroom" (relative to wall-to-wall carpet) (OR 3.50, p = 0.003) were associated with an increased risk of current eczema. All reported associations were independent of socioeconomic status (categorized by school), age and sex. This study suggests that household and country-specific environmental factors are associated with asthma, hay fever and eczema risk in 6-7-yr-old schoolchildren, and may have substantially contributed to the increased prevalence of these diseases in Australia.