Outdoor air pollution and asthma

PURPOSE OF REVIEW: The relation between outdoor air pollution and asthma has always been a major focus of research. The evidence that current levels of air pollution in many countries result in increased morbidity and mortality is fairly consistent. With rapid urbanization in many communities, traffic exhausts have become the major source of pollution, and many recent research studies have attempted to investigate the detrimental effects of this type of pollution. This paper reviews the recent evidence of the possible detrimental effects of ambient air pollution on the inception and morbidity of asthma. RECENT FINDINGS: Traffic related pollution has been confirmed in both cross-sectional and longitudinal studies to be associated with increased asthma morbidity and cardiopulmonary mortality. There is also evidence that pollutants such as ozone and traffic exhausts may be responsible for new incident cases of asthma. Among the particulate pollution, research investigating the ultrafine particles and the bacterial components suggested that these particles may have important role in asthma morbidity. SUMMARY: More research studies are needed to reveal how various air pollutants may interact with the host systems, such as the immune system, leading to increased morbidity in susceptible individuals. Reduction of the current levels of ambient air pollution should be an integral part of the overall effort in minimizing asthma morbidity or mortality in the community.     

The effects of air pollution on acute respiratory conditions

OBJECTIVE: Air pollution and its potential health effects are very important worldwide. It is particularly problematic in densely populated cities of developing countries that suffer from a lack of both short- and long-term programmes for air pollution control. We decided to study the short-term effects of air pollution on lung health by assessing the relationship between the levels of six air pollutants and emergency visits for asthma and COPD exacerbations in Tehran, Iran. METHODOLOGY: We monitored the daily attendances for acute respiratory conditions (asthma attacks and COPD exacerbations) to the emergency departments of five major hospitals together with the daily concentrations of six major pollutants during a 5-month period in Tehran. The association between these acute respiratory conditions and the levels of air pollutants was determined by multiple stepwise regression. RESULTS: A correlation was observed between the number of hospital admissions for asthma and the weekly mean concentration of nitrogen dioxide (P < 0.05). The 3-day and 10-day mean concentrations of sulphur dioxide were also found to be directly associated with the number of asthma admissions during this period (P < 0.05). No direct correlation was observed for other variables. CONCLUSION: This study further emphasizes the deleterious effects of air pollution on respiratory health in major populated cities such as Tehran and suggests that increased attention needs to be given to urgent control of air pollution problems.     

Air pollution and allergic disease

Over the past several decades, there has been increased awareness of the health effects of air pollution and much debate regarding the role of global warming. The prevalence of asthma and allergic disease has risen in industrialized countries, and most epidemiologic studies focus on possible causalities between air pollution and these conditions. This review examines salient articles and summarizes findings important to the interaction between allergies and air pollution, specifically volatile organic compounds, global warming, particulate pollutants, atopic risk, indoor air pollution, and prenatal exposure. Further work is necessary to determine whether patients predisposed to developing allergic disease may be more susceptible to the health effects of air pollutants due to the direct interaction between IgE-mediated disease and air pollutants. Until we have more definitive answers, patient education about the importance of good indoor air quality in the home and workplace is essential. Health care providers and the general community should also support public policy designed to improve outdoor air quality by developing programs that provide incentives for industry to comply with controlling pollution emissions.     

Chronic effects of air pollution on respiratory health in Southern California children: findings from the Southern California Children’s Health Study

Outdoor air pollution is one of the leading contributors to adverse respiratory health outcomes in urban areas around the world. Children are highly sensitive to the adverse effects of air pollution due to their rapidly growing lungs, incomplete immune and metabolic functions, patterns of ventilation and high levels of outdoor activity. The Children’s Health Study (CHS) is a continuing series of longitudinal studies that first began in 1993 and has focused on demonstrating the chronic impacts of air pollution on respiratory illnesses from early childhood through adolescence. A large body of evidence from the CHS has documented that exposures to both regional ambient air and traffic-related pollutants are associated with increased asthma prevalence, new-onset asthma, risk of bronchitis and wheezing, deficits of lung function growth, and airway inflammation. These associations may be modulated by key genes involved in oxidative-nitrosative stress pathways via gene-environment interactions. Despite successful efforts to reduce pollution over the past 40 years, air pollution at the current levels still brings many challenges to public health. To further ameliorate adverse health effects attributable to air pollution, many more toxic pollutants may require regulation and control of motor vehicle emissions and other combustion sources may need to be strengthened. Individual interventions based on personal susceptibility may be needed to protect children’s health while control measures are being implemented.     

Air pollution and chronic airway diseases: what should people know and do?

The health effects of air pollution remain a public health concern worldwide. Exposure to air pollution has many substantial adverse effects on human health. Globally, seven million deaths were attributable to the joint effects of household and ambient air pollution. Subjects with chronic respiratory diseases such as chronic obstructive pulmonary disease (COPD) and asthma are especially vulnerable to the detrimental effects of air pollutants. Air pollution can induce the acute exacerbation of COPD and onset of asthma, increase the respiratory morbidity and mortality. The health effects of air pollution depend on the components and sources of pollutants, which varied with countries, seasons, and times. Combustion of solid fuels is a major source of air pollutants in developing countries. To reduce the detrimental effects of air pollution, people especially those with COPD or asthma should be aware of the air quality and take extra measures such as reducing the time outdoor and wearing masks when necessary. For reducing the air pollutants indoor, people should use clean fuels and improve the stoves so as to burn fuel more efficiently and vent emissions to the outside. Air cleaners that can improve the air quality efficiently are recommended.     

Air pollution induced asthma and alterations in cytokine patterns

In recent decades, clinicians and scientists have witnessed a significant increase in the prevalence of allergic rhinitis and asthma. The factors underlying this phenomenon are clearly complex; however, this rapid increase in the burden of atopic disease has occurred in parallel with rapid industrialization and urbanization in many parts of the world. Consequently, more people are exposed to air pollutants than at any point in human history. Worldwide increases in allergic respiratory disease have mainly been observed in urban communities. Epidemiologic and clinical investigations have suggested a strong link between particulate air pollution and detrimental health effects, including cardiopulmonary morbidity and mortality. The purpose of this review is to provide an evidence-based summary of the effects of air pollutants on asthma, focusing on particulate matter PMs, diesel exhaust particles (DEPs), and ozone as major air pollutants. An overview of observational and experimental studies linking these pollutants with asthma will be provided, followed by consideration of the mechanisms underlying pollutant induced immune response and inflammation. The cytokine response will be viewed in depth and a brief discussion of future research and clinical directions is provided.     

Diesel fumes and the rising prevalence of atopy: An urban legend?

Recently, the incidence of allergic diseases has increased in most industrialized countries of the world. Persistent exposure to particulate air pollution from motor vehicles has been implicated as one of the factors that is responsible for the observed increased prevalence of atopy. Epidemiologic studies conducted in different parts of the world have demonstrated an important association between ambient levels of motor vehicle traffic emissions and increased symptoms of asthma and rhinitis. Additionally, recent human and animal laboratory-based studies have shown that particulate toxic pollutants, and in particular diesel exhaust particles (DEP), can enhance allergic inflammation and induce the development of allergic immune responses. In this article, our current understanding of the mechanisms by which pollutants such as DEPs enhance the underlying allergic inflammatory response is reviewed, and the evidence that supports the causative link between particulate air pollution from motor vehicles and increasing allergic diseases is discussed.     

Does outdoor air pollution induce new cases of asthma? Biological plausibility and evidence; a review

It is widely accepted that air pollution can exacerbate asthma in those who already have the condition. What is less clear is whether air pollution can contribute to the initiation of new cases of asthma. Mechanistic evidence from toxicological studies, together with recent information on genes that predispose towards the development of asthma, suggests that this is biologically plausible, particularly in the light of the current understanding of asthma as a complex disease with a variety of phenotypes. The epidemiological evidence for associations between ambient levels of air pollutants and asthma prevalence at a whole community level is unconvincing; meta-analysis confirms a lack of association. In contrast, a meta-analysis of cohort studies found an association between asthma incidence and within-community variations in air pollution (largely traffic dominated). Similarly, a systematic review suggests an association of asthma prevalence with exposure to traffic, although only in those living very close to heavily trafficked roads carrying a lot of trucks. Based on this evidence, the U.K.'s Committee on the Medical Effects of Air Pollutants recently concluded that, overall, the evidence is consistent with the possibility that outdoor air pollution might play a role in causing asthma in susceptible individuals living very close to busy roads carrying a lot of truck traffic. Nonetheless, the effect on public health is unlikely to be large: air pollutants are likely to make only a small contribution, compared with other factors, in the development of asthma, and in only a small proportion of the population.     

The 21st century environment and air quality influences on asthma

"Criteria" air pollutants are federally regulated pollutants that occur widely outdoors and have diverse sources, most often related to combustion. They include ozone (O3), particulate matter, sulfur dioxide (SO2), nitrogen dioxide (NO2), carbon monoxide (CO), and lead. All except lead may interfere with oxygen delivery, and so may be of special concern to asthmatics. In controlled experiments, SO2 causes acute asthma symptoms and bronchoconstriction, preventable by beta-agonist medications. Ozone causes acute irritant symptoms, restrictive lung dysfunction, increased bronchial reactivity, and lower-airway inflammation in healthy people and asthmatics. Exposures to O3, and possibly to other pollutants, appear to exacerbate bronchoconstrictive or inflammatory responses to inhaled aeroallergens (bioaerosols); this may represent an important health risk to asthmatics. Exposure levels known to evoke acute responses to O3 or SO2 are uncommon in community air pollution; however, some asthmatics might be susceptible to lesser, more common exposures. Evidence concerning NO2 is equivocal, but it may have O3-like effects in some asthmatics. Epidemiology has often associated particulate pollution with asthma exacerbations and other cardiorespiratory illnesses, even in cities with relatively mild air pollution. Current laboratory research cannot fully explain this association. Advances in emission controls should further reduce ambient pollution levels, but probably will not reduce asthma morbidity. Better asthma management, with improved anti-inflammatory medications, more careful monitoring by patients and health care providers, and reasonable efforts to reduce pollutant and aeroallergen exposures, offers the best hope to reduce asthma morbidity in the new century.     

Air pollution from traffic and the development of respiratory infections and asthmatic and allergic symptoms in children

Despite the important contribution of traffic sources to urban air quality, relatively few studies have evaluated the effects of traffic-related air pollution on health, such as its influence on the development of asthma and other childhood respiratory diseases. We examined the relationship between traffic-related air pollution and the development of asthmatic/allergic symptoms and respiratory infections in a birth cohort (n approximately 4,000) study in The Netherlands. A validated model was used to assign outdoor concentrations of traffic-related air pollutants (nitrogen dioxide, particulate matter less than 2.5 micro m in aerodynamic diameter, and "soot") at the home of each subject of the cohort. Questionnaire-derived data on wheezing, dry nighttime cough, ear, nose, and throat infections, skin rash, and physician-diagnosed asthma, bronchitis, influenza, and eczema at 2 years of age were analyzed in relation to air pollutants. Adjusted odds ratios for wheezing, physician-diagnosed asthma, ear/nose/throat infections, and flu/serious colds indicated positive associations with air pollutants, some of which reached borderline statistical significance. No associations were observed for the other health outcomes analyzed. Sensitivity analyses generally supported these results and suggested somewhat stronger associations with traffic, for asthma that was diagnosed before 1 year of age. These findings are subject to confirmation at older ages, when asthma can be more readily diagnosed.     

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.     

Gene-air pollution interaction and cardiovascular disease: a review

Genetic susceptibility is likely to play a role in response to air pollution. Hence, gene-environment interaction studies can be a tool for exploring the mechanisms and the importance of the pathway in the association between air pollution and a cardiovascular outcome.In this article, we present a systematic review of the studies that have examined gene-environment interactions in relation to the cardiovascular health effects of air pollutants.We identified 16 articles meeting our search criteria. Of these studies, most have focused on individual functional polymorphisms or individual candidate genes. Moreover, they were all based on 3 study populations that have been extensively investigated in relation to air pollution effects: the Normative Aging Study, Air Pollution and Inflammatory Response in Myocardial Infarction Survivors: Gene-Environment Interaction in a High Risk Group, and Multiethnic Study of Atherosclerosis.In conclusions, the studies differed substantially in both the cardiovascular outcomes examined and the polymorphisms examined, so there is little confirmation of results across cohorts. Gene-environment interaction studies can help explore the mechanisms and the potential pathway in the association between air pollution and a cardiovascular outcome; replication of findings and studies involving multiple cohorts would be needed to draw stronger conclusions.     

Adverse effects of outdoor pollution in the elderly

With fewer newborns and people living longer, older people are making up an increasing fraction of the total population. Epidemiological evidence shows that older-age-related health problems affect a wide and expanding proportion of the world population. One of the major epidemiological trends of this century is the rise of chronic diseases that affect more elderly than younger people. A total of 3.7 million premature deaths worldwide in 2012 are attributable to outdoor air pollution; the susceptibility to adverse effects of air pollution is expected to differ widely between people and within the same person, and also over time. Frailty history, a measure of multi-system decline, modifies cumulative associations between air pollution and lung function. Moreover, pre-existing diseases may determine susceptibility. In the elderly, due to comorbidity, exposure to air pollutants may even be fatal. Rapid and not-well-planned urbanization is associated with high level of ambient air pollution, mainly caused by vehicular exhausts. In general, there is sufficient evidence of the adverse effects related to short-term exposure, while fewer studies have addressed the longer-term health effects. Increased pollution exposures have been associated with increased mortality, hospital admissions/emergency-room visits, mainly due to exacerbations of chronic diseases or to respiratory tract infections (e.g., pneumonia). These effects may also be modulated by ambient temperature and many studies show that the elderly are mostly vulnerable to heat waves. The association between heat and mortality in the elderly is well-documented, while less is known regarding the associations with hospital admissions. Chronic exposure to elevated levels of air pollution has been related to the incidence of chronic obstructive pulmonary disease (COPD), chronic bronchitis (CB), asthma, and emphysema. There is also growing evidence suggesting adverse effects on lung function related to long-term exposure to ambient air pollution. Few studies have assessed long-term mortality in the elderly. It is still unclear what are the pollutants most damaging to the health of the elderly. It seems that elderly subjects are more vulnerable to particulate matter (PM) than to other pollutants, with particular effect on daily cardio-respiratory mortality and acute hospital admissions. Not many studies have targeted elderly people specifically, as well as specific respiratory morbidity. Most data have shown higher risks in the elderly compared to the rest of the population. Future epidemiological cohort studies need to keep investigating the health effects of air pollutants (mainly cardiopulmonary diseases) on the elderly.     

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.     

空气污染与儿童哮喘

工业化导致的空气污染是儿童哮喘发生、发展的高危因素之一。常见的空气污染物种类繁多,如交通相关空气污染物、多环芳香烃、香烟烟雾、尘埃颗粒及细颗粒物 PM 2.5等,均与儿童哮喘密切相关。它们通过各种相关信号通路,从而调节哮喘进程;同时空气污染导致的哮喘相关基因表观遗传学改变、上皮间充质转化及遗传多态性等亦影响儿童哮喘个体异质性及诊疗个体化。目前,空气污染与儿童哮喘研究已取得一定进展,但其确切机制仍需进一步研究。本文就常见的空气污染物参与儿童哮喘的发生、发展及其机制进行阐述。     

Air pollution and child respiratory health: a case-crossover study in Australia and New Zealand

RATIONALE: The strength of the association between outdoor air pollution and hospital admissions in children has not yet been well defined. OBJECTIVES: To estimate the impact of outdoor air pollution on respiratory morbidity in children after controlling for the confounding effects of weather, season, and other pollutants. METHODS: The study used data on respiratory hospital admissions in children (three age groups: < 1, 1-4, and 5-14 years) for five cities in Australia and two in New Zealand. Time series of daily numbers of hospital admissions were analyzed using the case-crossover method; the results from cities were combined using a random-effects meta-analysis. MEASUREMENTS AND MAIN RESULTS: Significant increases across the cities were observed for hospital admissions in children for pneumonia and acute bronchitis (0, 1-4 years), respiratory disease (0, 1-4, 5-14 years), and asthma (5-14 years). These increases were found for particulate matter with a diameter less than 2.5 microm (PM2.5) and less than 10 microm (PM10), nephelometry, NO2, and SO2. The largest association found was a 6.0% increase in asthma admissions (5-14 years) in relation to a 5.1-ppb increase in 24-hour NO2. CONCLUSIONS: This study found strong and consistent associations between outdoor air pollution and short-term increases in childhood hospital admissions. A number of different pollutants showed significant associations, and these were distinct from any temperature (warm or cool) effects.     

Levels of pollutants in indoor air and respiratory health in preschool children: A systematic review

The aim of this paper is thus to identify, evluate, and summarize in a systematic fashion all the epidemiological studies that have analyzed the association between exposure to specific indoor air pollutants and respiratory disease among children under the age of five. A search was carried out in the main biomedical bibliographica sources in December 2006 and updated in February 2008. The study period covered 12 years (1996–2007). All the selected papers were carefully read. We focused on studies that analyzed at least one indicator of respiratory health and which included one or more indoor air pollutants in relation to the respiratory health of children under the age of 5. Studies that analyzed passive smoking as the sole source of indoor air pollution were not included. Fourteen studies were considered to be relevant. The most analyzed pollutant was nitrogen dioxide, followed by volative organic compounds, airborne particulates and other pollutants; phthalates and CO₂. The literature reviewed within our criteria seems to indicate that several indoor pollutants, even at the moderate levels found in the developed countries, could be harmful to the respiratory health of very young children. Future research should focus on conducting more studies, preferably making use of cohorts, with adequate techniques for measuring indooor pollution levels. Pediatr Pulmonol. 2009; 44:231–243. © 2009 Wiley‐Liss, Inc.     

Pollution de l’air et asthme de l’enfant

The prevalence of asthma and allergic diseases doubled during the last quarter of the 20th century, particularly among children and adolescents. Given this fact, we cannot attribute this increase exclusively to genetic factors. Environmental factors to which it has been attributed include exposure to allergens and to airborne physicochemical pollutants, and changes in the characteristics of respiratory infections in young infants. In this review, we will point out the role of exposure to air pollutants and their interaction with other environmental factors. Whereas concentrations of the ‘classical’ air quality indicators (SO₂, CO) have more or less decreased steadily in developed countries, asthma prevalence has increased during the same period. However, the relation between the increase incidence of asthma and atmospheric pollution should be examined with the knwoledge that there has been an increase in new forms of pollution, in particular, ultrafine particles. There are at present many experimental studies which show that urban pollution (especially that associated with diesel exhaust particles) elicits chronic oxidative stress, bronchial hyperreactivity and allergic inflammation. Several epidemiological studies suggest that there is an association between the density of automobile traffic and the prevalence of respiratory symptoms, especially asthma and allergic rhinitis. Exposure to automobile traffic-related pollutants during early infancy may accelerate or even provoke, among genetically susceptible subjects, bronchial inflammatory processes which could contribute to the increase in the incidence of asthma in industrialized countries.     

Urban air pollution at the crossroads of the allergic pandemic

In these past decades an important increase in the prevalence of allergic respiratory diseases has been documented in most countries of the world with large differences being reported within different areas, particularly in industrialized countries. Persistent environmental exposure to particulate air pollution from motor vehicles has been suggested to be an important factor contributing to the observed increased prevalence of allergic diseases. Data from various investigators in different parts of the world have shown an important association between environmental levels of motor vehicle exhaust emissions and increased symptoms of asthma and rhinitis. In addition, recent human and animal laboratory-based studies have shown that particulate toxic pollutants, and especially diesel exhaust particles, can enhance allergic inflammation and induce the development of allergic immune responses. This article reviews the current state of knowledge on the role of diesel exhaust particles in the susceptibility to allergy. It scrutinizes the epidemiological evidence that supports the causative link between particulate air pollution from motor vehicles and the increasing prevalence in allergic conditions and the immunologic mechanisms by which diesel exhaust particles enhance the susceptibility to allergy.