2013 Research Highlights
Air pollution and health
Peter J Raymond/ Science Photo Library
Published Online December 23, 2013 http://dx.doi.org/10.1016/ S2213-2600(13)70284-4
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The detrimental health effects of air pollution have always attracted intense interest among researchers from around the world. In 2010, WHO estimated that more than 6 million people die prematurely every year because of air pollution.1 Both ambient air pollution and indoor air pollution have been linked to various adverse health outcomes, especially in people with pre-existing medical conditions. Although it might seem obvious that air pollution can affect people with pre-existing airway diseases, there are few controlled human exposure studies that can provide irrefutable evidence of adverse effects after acute exposure to an individual pollutant.2 Such controlled human exposure studies might also enable a better understanding of the underlying mechanisms leading to possible adverse outcomes.3 Ambient air contains many pollutants including gases such as ozone, oxides of nitrogen, and sulphur dioxide along with particulates of different sizes. Because of the complexity of the composition of air pollutants and the difficulty of precisely measuring exposure, identifying the role of different pollutants in respiratory morbidity is no simple task. Quantification of pollutant exposure in a study population is imprecise, because the levels of different components might vary with time and with the surroundings of the studied participants. Despite these difficulties, there have been several important reports published in 2013 that improve our understanding of the adverse health effects of air pollution.
Among the various pollutants, particulates with an aerodynamic diameter of less than 2·5 μm (PM2·5) have received a lot of attention recently. These small particles are able to penetrate deep into the small airways, alveoli, and blood stream, where they can lead to subsequent inflammation and vasocontriction. WHO has estimated that PM2·5 contribute to roughly 800 000 premature deaths per year globally.4 A systematic review, which pooled analyses of 35 observational studies, showed a strong and consistent association between admission to hospital with heart failure and exposure to PM2·5.5 With the exception of ozone, increases in other common pollutants such as carbon monoxide, sulphur dioxide, and nitrogen dioxide were also significantly associated with heart failure.5 The underlying mechanisms of such causal relations are probably complex, involving systemic inflammation and coronary vascular vasoconstriction associated with translocation of particulate matter into the systemic circulation. It is important to note that the present safe limits for different pollutants are associated with substantial morbidity and mortality. Although smoking is the most common cause of lung cancer, a recent study from the European Study of Cohorts for Air Pollution Effects,6 which included 17 cohorts from nine European countries including Norway, Sweden, Denmark, the UK, the Netherlands, Austria, Spain, Italy, and Greece, showed that exposure to PM2·5 and PM10 was associated with increased risk of adenocarcinoma of the lung. This study is one of the largest of its kind, and the methods used overcome major limitations of previous studies assessing the relation of air pollution and lung cancer. The metaanalyses showed that the hazard ratio for lung cancer and for PM2·5 was 1·18 per 5 μg/m³ and PM10 was 1·22 per 10 μg/m³. In addition to overcoming many limitations of previous similar studies, the strength of this meta-analysis was the inclusion of many participants from different European regions with varying levels of pollution, allowing the estimation of health risk. Similar to the relation of heart failure and air pollution, the health risk of lung cancer associated with exposure to particulate matter can occur at levels below the current European Union air quality limits.7 www.thelancet.com/respiratory Vol 2 January 2014
2013 Research Highlights
The results from this study, and that of Shah and colleagues,5 clearly call for measures to reduce such air pollution further and possible revision of the European Union limits for PM2·5 and PM10. In low-income countries, the major source of air pollution is the burning of biomass for cooking and heating. Women and young children are likely to be exposed to this type of pollution for longer periods than others because, in this setting, they spend more time in the home and in the kitchen. Although the relation of lower respiratory infections in children and exposure to household burning of biomass was consistent,8 the relation of such exposure and asthma is conflicting. Assessment of exposure is a major challenge because many factors can affect the total dose of pollutants inhaled by an individual; only a very large study would have the statistical power to overcome these limitations. The ISAAC phase 3 study group9 assessed the relation of open-fire cooking and asthma symptoms, and showed that open-fire cooking was associated with asthma symptoms and asthma diagnosis in two age groups: 6–7 years and 13–14 years. More than 500 000 children from 47 countries were included in this study. In the group of participants aged 6–7 years, exclusive use of an open fire for household cooking was associated with an odds ratio of 2·17 (95% CI 1·64–2·87) for wheezing in the past year, and this positive association was only identified in non-affluent countries. For a global study of this size, it would be extremely difficult to establish whether each individual participants with wheeze had atopic or non-atopic asthma. Nevertheless, reduction of such exposure to burning of biomass on a global level should be a major health priority, and prospective studies are needed to assess possible interventions. Obesity is associated with poor asthma control, and weight reduction in asthmatic individuals who are obese leads to improvement of asthma control.10 To understand the possible interaction between air pollution and obesity on the control of asthma, 148 children with asthma aged 5–17 years were assessed to establish the effect of weight on the relation between indoor pollutant exposure and asthma control.11 Most participants (91%) were
www.thelancet.com/respiratory Vol 2 January 2014
African-Americans and 28% of them were obese (as defined by a body-mass index at the 95th percentile or greater). Monitoring of airborne particulate matter in the child’s bedroom was done over a 5–7-day period. Asthma symptoms were significantly associated with exposure to PM2·5 in the obese group of children. Every ten-times increase in PM2·5 level was associated with a three to five times increase in the odds of cough in the absence of a viral infection in the obese group of children whereas there was only a doubling of odds of cough among children of normal weight. In view of this new knowledge regarding the detrimental effects of outdoor and indoor air pollution in both rich countries with the increasing problem of obesity and poor countries with major problems of indoor air pollution, a coordinated approach is urgently needed to reduce current levels of pollution, both indoors and outdoors. Gary W K Wong Department of Paediatrics, Prince of Wales Hospital, Shatin, Hong Kong [email protected] I declare that I have no conflicts of interest. 1
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Lim SS, Vos T, Flaxman AD, et al. A comparative risk assessment of burden of disease and injury attributable to 67 risk factors and risk factor clusters in 21 regions, 1990–2010: a systematic analysis for the Global Burden of Disease Study 2010. Lancet 2012; 380: 2224–60. Brunekreef B, Holgate ST. Air pollution and health. Lancet 2002; 360: 1233–42. Rom WN, Boushey H, Caplan A. Experimental human exposure to air pollutants is essential to understand adverse health effects. Am J Respir Cell Mol Biol 2013; 49: 691–96. WHO. World Health Report 2002. Geneva: World Health Organization, 2002. http://www.who.int/whr/2002/en/ (accessed Dec 12, 2013). Shah AS, Langrish JP, Nair H, et al. Global association of air pollution and heart failure: a systematic review and meta-analysis. Lancet 2013; 382: 1039–48. Raaschou-Nielsen O, Andersen ZJ, Beelen R, et al. Air pollution and lung cancer incidence in 17 European cohorts: prospective analyses from the European Study of Cohorts for Air Pollution Effects (ESCAPE). Lancet Oncol 2013; 14: 813–22. European Commission. Air quality standards. http://ec.europa.eu/ environment/air/quality/standards.htm (accessed Dec 16, 2013). Kodgule R, Salvi S. Exposure to biomass smoke as a cause for airway disease in women and children. Curr Opin Allergy Clin Immunol 2012; 12: 82–90. Wong GW, Brunekreef B, Ellwood P, et al. Cooking fuels and prevalence of asthma: a global analysis of phase three of the International Study of Asthma and Allergies in Childhood (ISAAC). Lancet Respir Med 2013; 1: 386–94. Boulet LP. Asthma and obesity. Clin Exp Allergy 2013; 43: 8–21. Lu KD, Breysse PN, Diette GB, et al. Being overweight increases susceptibility to indoor pollutants among urban children with asthma. J Allergy Clin Immunol 2013; 131: 1017–23.
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Air pollution and health
Peter J Raymond/ Science Photo Library
Published Online December 23, 2013 http://dx.doi.org/10.1016/ S2213-2600(13)70284-4
8
The detrimental health effects of air pollution have always attracted intense interest among researchers from around the world. In 2010, WHO estimated that more than 6 million people die prematurely every year because of air pollution.1 Both ambient air pollution and indoor air pollution have been linked to various adverse health outcomes, especially in people with pre-existing medical conditions. Although it might seem obvious that air pollution can affect people with pre-existing airway diseases, there are few controlled human exposure studies that can provide irrefutable evidence of adverse effects after acute exposure to an individual pollutant.2 Such controlled human exposure studies might also enable a better understanding of the underlying mechanisms leading to possible adverse outcomes.3 Ambient air contains many pollutants including gases such as ozone, oxides of nitrogen, and sulphur dioxide along with particulates of different sizes. Because of the complexity of the composition of air pollutants and the difficulty of precisely measuring exposure, identifying the role of different pollutants in respiratory morbidity is no simple task. Quantification of pollutant exposure in a study population is imprecise, because the levels of different components might vary with time and with the surroundings of the studied participants. Despite these difficulties, there have been several important reports published in 2013 that improve our understanding of the adverse health effects of air pollution.
Among the various pollutants, particulates with an aerodynamic diameter of less than 2·5 μm (PM2·5) have received a lot of attention recently. These small particles are able to penetrate deep into the small airways, alveoli, and blood stream, where they can lead to subsequent inflammation and vasocontriction. WHO has estimated that PM2·5 contribute to roughly 800 000 premature deaths per year globally.4 A systematic review, which pooled analyses of 35 observational studies, showed a strong and consistent association between admission to hospital with heart failure and exposure to PM2·5.5 With the exception of ozone, increases in other common pollutants such as carbon monoxide, sulphur dioxide, and nitrogen dioxide were also significantly associated with heart failure.5 The underlying mechanisms of such causal relations are probably complex, involving systemic inflammation and coronary vascular vasoconstriction associated with translocation of particulate matter into the systemic circulation. It is important to note that the present safe limits for different pollutants are associated with substantial morbidity and mortality. Although smoking is the most common cause of lung cancer, a recent study from the European Study of Cohorts for Air Pollution Effects,6 which included 17 cohorts from nine European countries including Norway, Sweden, Denmark, the UK, the Netherlands, Austria, Spain, Italy, and Greece, showed that exposure to PM2·5 and PM10 was associated with increased risk of adenocarcinoma of the lung. This study is one of the largest of its kind, and the methods used overcome major limitations of previous studies assessing the relation of air pollution and lung cancer. The metaanalyses showed that the hazard ratio for lung cancer and for PM2·5 was 1·18 per 5 μg/m³ and PM10 was 1·22 per 10 μg/m³. In addition to overcoming many limitations of previous similar studies, the strength of this meta-analysis was the inclusion of many participants from different European regions with varying levels of pollution, allowing the estimation of health risk. Similar to the relation of heart failure and air pollution, the health risk of lung cancer associated with exposure to particulate matter can occur at levels below the current European Union air quality limits.7 www.thelancet.com/respiratory Vol 2 January 2014
2013 Research Highlights
The results from this study, and that of Shah and colleagues,5 clearly call for measures to reduce such air pollution further and possible revision of the European Union limits for PM2·5 and PM10. In low-income countries, the major source of air pollution is the burning of biomass for cooking and heating. Women and young children are likely to be exposed to this type of pollution for longer periods than others because, in this setting, they spend more time in the home and in the kitchen. Although the relation of lower respiratory infections in children and exposure to household burning of biomass was consistent,8 the relation of such exposure and asthma is conflicting. Assessment of exposure is a major challenge because many factors can affect the total dose of pollutants inhaled by an individual; only a very large study would have the statistical power to overcome these limitations. The ISAAC phase 3 study group9 assessed the relation of open-fire cooking and asthma symptoms, and showed that open-fire cooking was associated with asthma symptoms and asthma diagnosis in two age groups: 6–7 years and 13–14 years. More than 500 000 children from 47 countries were included in this study. In the group of participants aged 6–7 years, exclusive use of an open fire for household cooking was associated with an odds ratio of 2·17 (95% CI 1·64–2·87) for wheezing in the past year, and this positive association was only identified in non-affluent countries. For a global study of this size, it would be extremely difficult to establish whether each individual participants with wheeze had atopic or non-atopic asthma. Nevertheless, reduction of such exposure to burning of biomass on a global level should be a major health priority, and prospective studies are needed to assess possible interventions. Obesity is associated with poor asthma control, and weight reduction in asthmatic individuals who are obese leads to improvement of asthma control.10 To understand the possible interaction between air pollution and obesity on the control of asthma, 148 children with asthma aged 5–17 years were assessed to establish the effect of weight on the relation between indoor pollutant exposure and asthma control.11 Most participants (91%) were
www.thelancet.com/respiratory Vol 2 January 2014
African-Americans and 28% of them were obese (as defined by a body-mass index at the 95th percentile or greater). Monitoring of airborne particulate matter in the child’s bedroom was done over a 5–7-day period. Asthma symptoms were significantly associated with exposure to PM2·5 in the obese group of children. Every ten-times increase in PM2·5 level was associated with a three to five times increase in the odds of cough in the absence of a viral infection in the obese group of children whereas there was only a doubling of odds of cough among children of normal weight. In view of this new knowledge regarding the detrimental effects of outdoor and indoor air pollution in both rich countries with the increasing problem of obesity and poor countries with major problems of indoor air pollution, a coordinated approach is urgently needed to reduce current levels of pollution, both indoors and outdoors. Gary W K Wong Department of Paediatrics, Prince of Wales Hospital, Shatin, Hong Kong [email protected] I declare that I have no conflicts of interest. 1
2 3
4 5
6
7 8
9
10 11
Lim SS, Vos T, Flaxman AD, et al. A comparative risk assessment of burden of disease and injury attributable to 67 risk factors and risk factor clusters in 21 regions, 1990–2010: a systematic analysis for the Global Burden of Disease Study 2010. Lancet 2012; 380: 2224–60. Brunekreef B, Holgate ST. Air pollution and health. Lancet 2002; 360: 1233–42. Rom WN, Boushey H, Caplan A. Experimental human exposure to air pollutants is essential to understand adverse health effects. Am J Respir Cell Mol Biol 2013; 49: 691–96. WHO. World Health Report 2002. Geneva: World Health Organization, 2002. http://www.who.int/whr/2002/en/ (accessed Dec 12, 2013). Shah AS, Langrish JP, Nair H, et al. Global association of air pollution and heart failure: a systematic review and meta-analysis. Lancet 2013; 382: 1039–48. Raaschou-Nielsen O, Andersen ZJ, Beelen R, et al. Air pollution and lung cancer incidence in 17 European cohorts: prospective analyses from the European Study of Cohorts for Air Pollution Effects (ESCAPE). Lancet Oncol 2013; 14: 813–22. European Commission. Air quality standards. http://ec.europa.eu/ environment/air/quality/standards.htm (accessed Dec 16, 2013). Kodgule R, Salvi S. Exposure to biomass smoke as a cause for airway disease in women and children. Curr Opin Allergy Clin Immunol 2012; 12: 82–90. Wong GW, Brunekreef B, Ellwood P, et al. Cooking fuels and prevalence of asthma: a global analysis of phase three of the International Study of Asthma and Allergies in Childhood (ISAAC). Lancet Respir Med 2013; 1: 386–94. Boulet LP. Asthma and obesity. Clin Exp Allergy 2013; 43: 8–21. Lu KD, Breysse PN, Diette GB, et al. Being overweight increases susceptibility to indoor pollutants among urban children with asthma. J Allergy Clin Immunol 2013; 131: 1017–23.
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