Schikowski et al Respiratory Research 2010, 11:113 http://respiratory-research.com/content/11/1/113 RESEARCH Open Access Decline in air pollution and change in prevalence in respiratory symptoms and chronic obstructive pulmonary disease in elderly women Tamara Schikowski1,2,3*, Ulrich Ranft1, Dorothee Sugiri1, Andrea Vierkötter1, Thomas Brüning4, Volker Harth4, Ursula Krämer1 Abstract Background: While adverse effects of exposure to air pollutants on respiratory health are well studied, little is known about the effect of a reduction in air pollutants on chronic respiratory symptoms and diseases We investigated whether different declines in air pollution levels in industrialised and rural areas in Germany were associated with changes in respiratory health over a period of about 20 years Methods: We used data from the SALIA cohort study in Germany (Study on the influence of Air pollution on Lung function, Inflammation and Aging) to assess the association between the prevalence of chronic obstructive pulmonary disease (COPD) and chronic respiratory symptoms and the decline in air pollution exposure In 19851994, 4874 women aged 55-years took part in the baseline investigation Of these, 2116 participated in a questionnaire follow-up in 2006 and in a subgroup of 402 women lung function was tested in 2008-2009 Generalized estimating equation (GEE) models were used to estimate the effect of a reduction in air pollution on respiratory symptoms and diseases Results: Ambient air concentrations of particulate matter with aerodynamic size < 10 μm (PM10) declined in average by 20 μg/m3 Prevalence of chronic cough with phlegm production and mild COPD at baseline investigation compared to follow-up was 9.5% vs 13.3% and 8.6% vs 18.2%, respectively A steeper decline of PM10 was observed in the industrialized areas in comparison to the rural area, this was associated with a weaker increase in prevalence of respiratory symptoms and COPD Among women who never smoked, the prevalence of chronic cough with phlegm and mild COPD was estimated at 21.4% and 39.5%, respectively, if no air pollution reduction was assumed, and at 13.3% and 17.5%, respectively, if air pollution reduction was assumed Conclusion: We concluded that parallel to the decline of ambient air pollution over the last 20 years in the Ruhr area the age-related increase in chronic respiratory diseases and symptoms appears to attenuate in the population of elderly women Introduction Several epidemiological studies have shown that chronic exposure to high levels of air pollutants (PM 10 and NO2) has adverse effects on respiratory health These adverse effects on respiratory health are not limited to high concentrations of air pollutants, but have also been observed at relatively low concentrations It has been * Correspondence: tamara.schikowski@unibas.ch Department of Epidemiology Institut für Umweltmedizinische Forschung (IUF) at the Heinrich-Heine-University Düsseldorf, Düsseldorf, Germany Full list of author information is available at the end of the article previously reported that long-term exposure to air pollutants from traffic related sources reduce lung function [1-5] and influence chronic respiratory diseases [6-8] Furthermore, long-term exposure to air pollutants is known to be associated with cardiovascular mortality [9-12] and increased hospital admissions [13-16] However, less is known about the effect of a reduction in air pollutants on chronic respiratory symptoms and diseases, including chronic cough Chronic cough is common in people aged 70 and over and the prevalence increases further with age [17-21] Additionally, chronic © 2010 Schikowski et al; licensee BioMed Central Ltd This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited Schikowski et al Respiratory Research 2010, 11:113 http://respiratory-research.com/content/11/1/113 cough may also be the first symptom in the development of chronic obstructive pulmonary disease [21,22] There is evidence that a reduction in air pollutants attenuates the decline in respiratory health in children The delay in lung function development, due to air pollutants, attenuates when the children move to cleaner areas [23,24] Moreover, a recent prospective cohort study of adults living in Switzerland, the Swiss study on Air Pollution and Lung Disease in Adults (SAPALDIA), showed that a decline in lung function [25], as well as an increase of respiratory symptoms [26], is attenuated by a reduction in exposure to PM10 However, the effect of a reduction in air pollutants on respiratory health in elderly people has not been analysed so far In the present study, we investigated whether the agerelated increase of respiratory symptoms and diseases is attenuated by a reduction in exposure to ambient air pollutants using data collected from the SALIA study (the Study on the influence of Air pollution on Lung function, Inflammation and Aging), a prospective cohort of elderly women living in the highly industrialised Ruhr district and in adjacent rural areas in Germany Chronic respiratory symptoms and lung function were first measured in 1985-1994, when ambient air pollution exposure was high, and follow-up was conducted from 2006 to 2009, when concentrations of ambient air pollutants in the Ruhr district had been considerably reduced Thus, we were provided with sufficient power to examine whether the changes in prevalence of respiratory symptoms and disease were attenuated by reduction in ambient air pollutants Materials and methods Design and study population The SALIA study was initiated in the early 1980 s by the North Rhine-Westphalia State Government to investigate the effect of air pollution exposure in women The study population was a sample of women from the Ruhr area, Germany, and two rural areas in the North of the Ruhr area Health examinations were conducted between 1985 and 1994 in 4874 women, who were all approximately 55-years of age at the time of examination Health examinations included lung function measurements for a subset of the participants (n = 2,593) Previous results of the baseline investigation showed that exposure to high concentrations of air pollutants reduces lung function and was associated with COPD [6,10] In 2006, a follow-up study of the same women was conducted to assess the changes in respiratory symptoms and diseases in these women after a strong decline in concentrations of ambient air pollutants in the Ruhr area A questionnaire about respiratory health and its risk factors was sent out to all surviving participants, each of whom received three reminder letters Page of 11 Completed questionnaires were received from 2116 (53%) of the surviving participants In 2007 to 2009 a follow-up examination in a subgroup of the study population was conducted This subgroup consisted of 706 women who had a lung function measurement at baseline and who agreed to further examinations in the questionnaire follow-up in 2006 The women were invited in a randomized manner from four cities in the Ruhr area (Duisburg, Dortmund, Essen and Gelsenkirchen), as well as the rural county of Borken, which was used as a reference area In total, 402 women, who were aged 70 to 80 years old, participated and lung function testing was completed in 395 of these participants Figure gives a flow chart of the SALIA cohort study between baseline investigation and follow-up The present analysis was restricted to the women who had complete information on respiratory health outcomes at baseline investigation and at the follow-up Approval of the study was obtained from the Ethical Committee of the University of Bochum We received written informed consent from all participants Assessment of respiratory health and risk factors by questionnaire Together with an invitation to participate in the baseline investigation, the women received a self-administered questionnaire about respiratory health and its risk factors The same questions regarding respiratory symptoms and diseases of the baseline investigation were used in the follow-up We asked whether a physician had ever diagnosed chronic bronchitis and additionally we asked for respiratory symptoms Respiratory symptoms were divided in two categories: “frequent cough in the morning or during the day a) without phlegm production or b) with phlegm production” We additionally collected information about the following known risk factors for respiratory diseases in the questionnaire: current and past smoking habits, passive smoking exposure at home or at work, indoor exposure by heating with fossil fuels, and occupational exposures to dust or fumes For smoking habits, the women were grouped as never smoker, passive smoker (at home or/and at work place), past smoker or current smoker We classified socioeconomic status at baseline into four categories using the highest school level achieved by either the women or her husbands as low (< 10 years), medium (= 10 years) or medium high (11-12 years) and high >12 years) Lung function measurement and COPD definition Spirometry was performed according to the ATS/ETS recommendations [25] Forced expiratory volume in second (FEV ) and forced vital capacity (FVC) were measured Between three to four manoeuvres were performed under direction of trained personnel, and the Schikowski et al Respiratory Research 2010, 11:113 http://respiratory-research.com/content/11/1/113 Page of 11 Figure Flowchart showing the SALIA collective from baseline till follow-up in 2007/2008 values where the maximal FEV1 was reached were used All measuring instruments were calibrated prior to each testing The technical personnel were trained and all results were reviewed by a pulmonary physician COPD was defined using the ratio FEV1/FVC, which is considered a sensitive measure of COPD on its own [26] We defined two forms of COPD: mild COPD (stage 1) was defined as FEV1/FVC ratio < 0.7 and the moderate form (stage 2) as FEV /FVC ratio 12 years - 11.0 - 11.0 - 12.2 2074 2077 2.0 23.3 2021 1997 5.4 53.4 401 400 9.7 66.3 Urban residency a Smoking status: Indoor exposure Education: Asthma Hypertension b SD: Standard deviation BMI: Body mass index (weight/height2) a Urban Duisburg, Dortmund, Essen, Gelsenkirchen; rural: Borken b Heating with fossil fuels (gas, coal or wood) respiratory symptoms at baseline and at follow-up was analyzed using generalised estimating equations (GEE) The individual change in exposure ΔE was calculated as the difference between the baseline measurement and the measurement at follow-up For multivariate regression modelling, we assumed linear dependency of the prevalence of chronic respiratory diseases and symptoms on exposure at baseline (E baseline), and on the time of follow-up t, since all women were 55 years of age at baseline Additionally, we investigated whether the age related increase in diseases or symptoms associated with the time of follow-up t was linearly modified by the change in exposure ΔE The GEE model controlled for a set of potential confounder (smoking behaviour, passive smoking, social status and exposure to indoor air pollutants) on an individual basis However inclusion of social status, indicated by school education, passive smoking and indoor air pollution exposure did not change the parameter estimates by more than 10% and were not included in the final model The final models were written as follows: p =  +  * E baseline +  * S baseline and p t =  +  * E baseline + ( +  *  E) * t +  * S baseline +  * S follow −up with: p0 prevalence at baseline, pt prevalence at followup, E baseline exposure at baseline, ΔE exposure decline (exposure at baseline minus exposure at follow-up), t follow-up time, Sbaseline smoking at baseline (yes = 1, no = 0) and Sfollow-up smoking at follow-up (yes = 1, no = 0) All statistical analyses were performed with SAS for windows release 9.1 (SAS Institute, Cary, NC) Results Characteristics of study participants The characteristics of the study cohort are presented in Table The majority of the study participants lived in cities of the Ruhr area The mean age of these women at the follow-up investigation in 2006 was 71.3 years Little change in body mass index (BMI) was observed Most women tended to give up smoking; similarly, passive smoke exposure was considerably reduced between baseline and follow-up investigation A reduction of heating with fossil fuels was reported throughout the areas The majority of women had a school education of 10 or more years A slight increase in reported asthma and a doubling of reported hypertension was observed between the baseline investigation and the follow-up Twelve per cent of the women were occupationally exposed to dust and fumes before baseline investigation, but not afterwards Occupational exposure to dust and fumes was not considered as a potential risk factor in the proceeding analysis More than 98% of the participants had not moved since baseline We also evaluated whether participants from the 2006 survey differed from non-participants Length of education was a primary differentiating factor; less than 10 years of schooling was reported by 21.6% of those responding at baseline, by 38.5% of those 595 women who died between baseline Schikowski et al Respiratory Research 2010, 11:113 http://respiratory-research.com/content/11/1/113 Page of 11 and follow up, and by 36.6% of those 1911 not responding but who were still alive We additionally examined whether the associations between air pollution and respiratory health as reported in a previous publication of the same cohort [28] differed between the responder groups, but did not detect any systematic differences; no significant interactions were observed between responder status and air pollution on respiratory health Table Distribution of long-term air pollution exposures among women living in the Ruhr area and an adjacent rural area in Germany at baseline and at follow-up Total Group (n = 2116) Baseline in 1985-1994 Follow-up in 2006 Change in rural area Change in urban area PM10 No2 PM10 NO2 PM10 NO2 PM10 NO2 Min 38.9 22.0 25.0 20.2 13.9 1.8 14.8 8.6 Prevalence of respiratory health outcomes 25 Percentile 42.6 24.4 25.0 20.2 14.3 2.6 16.2 13.4 The prevalence of chronic bronchitis, respiratory symptoms and COPD are shown in Table The prevalence of respiratory symptoms and chronic bronchitis by physician’s diagnosis increased between the baseline investigation and 2006 with increasing age of the participants Participants who had missing answers in the questionnaire were excluded from the analysis, so the numbers vary slightly from one respiratory health outcome to another Chronic cough was the most commonly reported respiratory symptom with a prevalence of 20.6% and 26.5% at baseline and at follow-up, respectively The prevalence of mild COPD assessed with FEV1/FVC < 0.7 at baseline was 8.6% and 18.2% at follow-up and, therefore, comparable to the prevalence of chronic cough with phlegm production Only a few participants were classified as having moderate COPD (n = 14 and n = 23, respectively) At the baseline investigation the prevalence of all respiratory symptoms and diseases was lower in the rural than in the urban areas whereas this was not true for the follow-up investigation Median 46.9 39.8 26.0 31.2 14.3 4.2 23.1 16.4 Mean 46.6 38.1 26.9 27.9 17.6 3.8 21.4 15.4 75 Percentile Max 52.1 53.6 49.8 28.4 61.0 30 32.8 44.6 21.9 24.0 4.8 6.3 24.6 25.2 17.2 21.2 Change in concentrations of PM10 and NO2 A strong decrease in air pollution levels was observed throughout the entire study area (Table 3) In particular, urban areas with high PM10 levels at baseline experienced a strong reduction in concentrations through to follow-up (Figure 2) Across the study areas, the 5-year mean PM10 concentrations declined on average from 46.6 μg to 26.9 μg (interquartile range: 10 μg/m3) A slightly weaker decline was observed for NO2 concentrations (Figure 3) In the rural area of Borken, NO concentrations remained stable during the 20 years of the follow-up, but the 5-year mean concentrations of NO decreased in average from 38.1 μg to 27.9 μg (interquartile range: 12.2 μg/m3) Decline in air pollution exposure and change of prevalence of respiratory health outcomes The association of decline in PM10 and NO2 pollution between baseline and follow-up with the prevalence of respiratory symptoms and diseases at baseline and at follow-up is presented in Table The table shows the mutually adjusted parameter estimates (prevalence change per unit) for smoking at baseline, change in Table Prevalence of respiratory symptoms, chronic bronchitis at baseline (1985 - 1994) and at follow-up (2006) and COPD at baseline (1985-1994) and at follow-up (2007/2008) in a subgroup of elderly women Prevalence Baseline Respiratory health outcome Follow-up all Ruhr area rural areas all Ruhr area rural areas N = 2073 (8.2%) N = 1167 (9.3%) N = 905 (6.6%) N = 2032 (11.6%) N = 1125 (13.6%) N = 90782 (9.0%) N = 2110 (20.6%) N = 1175 (22.7%) N = 935 (18.0%) N = 1947 (26.5) N = 1079 (27.9%) N = 868 (24.7%) N = 2099 (9.5%) N = 1168 10.1% N = 931 8,8% N = 1979 (13.3%) N = 1098 (13.5%) N = 890 (13.2%) Mild COPDb FEV1/FVC < 0.7 N = 384 (8.6%) N = 201 10.5% N = 183 6.6% N = 347 (18.2%) N = 179 (12.9%) N = 163 (22.7%) Moderate COPDbFEV1/FVC< 0.7 and FEV1< 80% predicted N = 384 (3.7%) N = 201 5.0% N = 183 2.2% N = 347 (6.6%) N = 179 (5.6%) N = 163 (8.0%) Chronic Bronchitis by physician’s diagnosis Chronic cough a Chronic cough with phlegm production a a a Reported by participant Only in a subgroup that was invited for the follow-up examination in 2007/2008 Women with asthma were excluded b Schikowski et al Respiratory Research 2010, 11:113 http://respiratory-research.com/content/11/1/113 Figure Annual mean concentrations of particulate matter with a diameter of less than 10 μm (PM10) Figure Annual mean concentrations of nitrogen dioxide (NO2) from 1982 to 2008 by study area Page of 11 Schikowski et al Respiratory Research 2010, 11:113 http://respiratory-research.com/content/11/1/113 Page of 11 Table Results of GEE regression analysis: Association of prevalence of chronic bronchitis, respiratory symptoms, and COPD with smoking at baseline and at follow up, exposure at baseline, follow-up time and exposure decline; coefficients are mutually adjusted Chronic bronchitis Chronic cough a PM10 Sample size NO2 PM10 1950 NO2 1902 Chronic cough with phlegm production PM10 NO2 Mild COPD PM10 1922 b NO2 Moderate COPD PM10 342 c NO2 342 Parameter estimates and 95% confidence interval (times 100) Intercept -1.514.33 0.2415.05 5.109.07 -2.813.9312.04;9.02 *0.94;7.73 14.85;15.33 *10.15;19.95 6.06;16.26 *5.48;12.67 28.64;23.01 3.47;11.33 Smoking at baseline 2.421.31;6.16 Smokingat follow-up Follow up time e Follow up time exposure decline 0.154.04;4.34 7.020.89;14.92 7.621.01;16.24 f 3.925.34;13.19 4.674.95;14.28 -1.20 -1.5714.59 -7.45;5.06 7.83;4.68; *5.86;23.32 d 13.99 5.92 6.08 *8.36;19.62 *1.64;10.20 *1.77;10.39 14.46 * 5.73;23.20 7.82 * 7.96 1.56;14.08 *1.83;14.09 -9.2527.72;9.22 -9.45–2.182.0427.38;8.48 16.06;11.69 16.02;11.93 2.012.32 0.25;4.26 *0.18;4.47 4.04 *0.80;7.28 2.690.40;5.77 0.821.56;3.20 2.353.24;7.94 2.971.99;7.94 2.221.82 12.58 2.24;6.69 *0.28;3.37 *5.80;19.36 Exposure at baseline 1.9513.94 1.66;5.57 *8.35;19.54 -15.52 *-24.83;6.21 5.37 *2.77;7.98 -0.174.37;4.03 -1.153.25;0.96 0.211.08;1.50 -8.17 *-14.54;1.79 -0.072.25;2.11 8.22 3.60 *3.07;13.37 *1.60;5.59 -5.39 *-10.22;0.57 -0.872.41;0.66 3.96 *1.60;6.32 2.050.96;5.06 20.61 9.12 8.02 *7.81;33.41 *4.78;13.46 *0.01;16.03 2.73 *0.03;5.43 -14.62 *-25.88;3.36 -4.64 *-8.03;1.26 -6.2013.33;0.94 -1.663.8;0.048 *p < 0.05 a Reported physician’s diagnosis b FEV1/FVC