Metanalysis: Respiratory Effects in the General Population Exposed to Urban Pollution

doi:10.4236/jep.2011.27112

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Journal of Environmental Protection, 2011, 2, 974-981

doi:10.4236/jep.2011.27112 Published Online September2011 (http://www.SciRP.org/journal/jep)

Metanalysis: Respiratory Effects in the General

Population Exposed to Urban Pollution

Angela Sancini, Francesco Tomei, Assunta Capozzella, Alessandro Pacchiarotti, Simone De Sio,

Gianfranco Tomei*, Paola Palermo, Manuela Ciarrocca

University of Rome “Sapienza”, Rome, Italy.

Email: *[email protected]

Received March 30th, 2011; revised July 14th, 2011; accepted August 24th, 2011.

ABSTRACT

Aim: The purpose of this study was to evaluate spirometric lung function parameters in the general population exposed

to urban pollution and confirm the existence of an association between exposure to environmental pollutants and effects

from these products and which respiratory parameters are associated to urban pollution in general population.

Methods: This study is a systematic research of all articles on the assessment of respiratory effects on general

population exposed to urban pollution, excluding studies on adolescents and children. The research included articles

from January 2008 to May 2009. In the articles included in our meta-analysis, the exposed group is represented by

general population aged between 15 and 75 years for both genders, resident in very polluted urban areas, while the

control group is represented by general population resident in rural and suburban areas, where pollution is lower.

Results: The results confirm the presence of statistica lly significant effects of urban pollu tion on the respiratory system

for cough, phlegm, shortness of breath/breathlessness, wheezing, FVC, FEV1, PEFR, chronic bronchitis, bronchial

asthma, rhinitis, emphysema.

Keywords: Urban Pollution, Respiratory Symptoms on General Population , Lung Disease, Environmental Exposure

1. Introduction

On the basis of the assessment conducted by WHO, urban

pollution is a very significant public health problem.

Studies of assessment have invariably shown that adverse

effects of air pollution on health are substantial.

Measures of containment have produced a reduction of

urban pollution levels, but results of recent studies

continue to emphasize acute and chronic effects on

health, even when these levels are low.

Epidemiological research has consistently documented

a wide range of adverse effects to human health for

exposure to pollutants: it has been documented a wide

range of adverse health outcomes due to short and long

term exposure to air pollutant concentration levels for

urban populations.

Numerous clinical and toxicological studies have

provided significant information about the specific

effects of pollutants and the possible mechanisms of

action these effects have.

General population is daily exposed to pollutants of

various kinds. These pollutants are made up of chemical

and physical (i.e. noise).

Furthermore, the presence of high levels of air pollu-

tion is connected to respiratory symptoms and disease in

various European and non European countries: in the

U.S., the presence of chronic bronchitis was significantly

associated with fine particle pollution [1].

In Italy it was shown that residents in a rural area have

prevalence rates of respiratory symptoms lower than

children who live in urban areas [21,22].

Another important European study has shown, in

adults, an increased risk of developing a framework of

bronchitis resulting from exposure to traffic pollution

from motor vehicles [2]. The respiratory symptoms of 40

- 59 year old women, who spent much of their time at

home, was related to the proximity of their residence to

high motor vehicle traffic areas[15]. Other studies to re-

member in this context are conducted on a population of

at least 10 years in metropolitan areas or rural areas,

where there has been a significant association between

symptoms of chronic obstructive respiratory disease and

high levels of particulates [3].

The purpose of this study was to evaluate spirometric

lung function parameters in the general population ex-

posed to urban pollution and confirm the existence of an

Metanalysis: Respiratory Effects in the General Population Exposed to Urban Pollution975

association between exposure to environmental pollu-

tants and effects from these products and which respira-

tory parameters are associated to urban pollution in gen-

eral population.

2. Materials and Methods

This study has been conducted with a systematic research

of all articles on the assessment of respiratory effects in

the general population exposed to urban pollution,

excluding studies on adolescents and children. The

research included articles from January 2008 (year of

enactment of Presidential Decree 203/88: “Implementa-

tion of directives CEE n. 80/779, 82/884, 84/360 and

85/203 that pertain to air quality directives, relatively to

specific pollutant and the pollution producted by industry,

pursuant to art. 15 of Law of April 16, 1987, number

183”) to May 2009.

We used the following electronic search engines,

available online:

 Biomedcentral

 MEDLINE/ PubMed

 MEDLINE/ National Library of Medicine (NLM)

 MEDLINE Plus

 Nioshtic-2

 Scopus

 TOXNET/Toxline

Furthermore we examined the acts of national con-

gresses organized by S.I.M.L.I.I. (Italian Society of Oc-

cupational Health and Industrial Hygiene) and by

A.I.D.I.I. (Italian Association of Industrial Hygienist)

and many books of Environmental health.

For all search engines we used the following key

words:

 Air pollution (or pollutant) and urban (or rural or

general) population

 Urban pollution (or pollutants) and urban (or rural or

general) population

 Urban air pollution and urban (or rural or general)

population

 Urban atmospheric pollution (or pollutant) and urban

(or rural or general) population

 Ambient air (pollution) and urban (or rural or general)

population

 Ambient exposure and urban (or rural or general)

population

 Environmental exposure and urban (or rural or gen-

eral) population

 Particulate matter (PM) and urban (or rural or general)

population

 Urban particulate matter (UPM) and urban (or rural or

general) population

 Ultrafine particulate matter and urban (or rural or

general) population

 Ultrafine particles (fine particles) and urban (or rural

or general) population

 Concentrated ambient fine particles (CAP) and urban

(or rural or general) population

 Volatile organic compounds (VOCs) and urban (or

rural or general) population

 Suspended particulate matter (SPM) and urban (or

rural or general) population

 Total suspended particulate matter (TSPM) and urban

(or rural or general) population

 Traffic emissions (air pollution) and urban (or rural or

general) population

 Urban traffic and urban (or rural or general) popula-

tion

 Road traffic (pollution) and urban (or rural or general)

population

 High (or heavy) traffic density and urban (or rural or

general) population

Of the 976 publications we found, 85 turned out to be

inherent with the aim of our study and only 22 responded

to the following inclusion criteria:

1) Case-Control studies, studies in which the

experimental group was composed of subjects vulnerable

to urban pollution and the control group was made up of

subjects exposed to a lower degree of urban pollution;

2) Studies that reported results in numerical terms of

media and standard deviation (for the continues variables)

or of frequency (for not continue variables); their main

characteristics are reported in Tables 1-3.

We tried to contact the authors of publications in

which the results were expressed in unvailable numeric

form, to obtain substantial data but did not have any

answer.

3. Description of Participants

In the articles included in our meta-analysis, the exposed

group is represented by general population aged between

15 and 75 years for both gender, resident in most

polluted urban areas, while the control group is re-

presented by general population resident in rural and

suburban areas, where pollution is lower.

The numbers of participants included in this meta-

analysis is 48.848; the number of cases is 22.414 while

the number of controls is 26.434.

In the studies, where is specified, total number of male

subjects in the case group is 10.357 while the number of

female is 10.965. In the studies, where is specified, total

number of male subjects in the control group is 13.457

while the number of female is 12.136.

4. Data Organization

After a careful analysis of selected studies we have

identified the most frequently studied variables on the

Metanalysis: Respiratory Effects in the General Population Exposed to Urban Pollution

976

Table 1. Distribution of studies included in the variables.

Class Variables Authors To

Cough

Van der Zee et al. 2000; Bjornsson et al. 1994; Viegi et al. 1991; Viegi et al. 1999; Viegi et al. 2004;

Sunyer et al. 2006; Devereux et al. 1996; Walraven et al. 2001; Kumar et al. 2000;

Sekine et al. 2004; Jedrychowski et al. 1989.

Phlegm Van der Zee et al. 2000; Viegi et al. 1991; Viegi et al. 1999; Viegi et al. 2004; Sunyer et al. 2006;

Kumar et al. 2000; Sekine et al. 2004; Jedrychowski et al. 1989. 8

Dyspnea Viegi et al. 1991; Viegi et al. 1999; Viegi et al. 2004; Jedrychowski et al. 1989. 4

Short

breath/breathless

ness

Devereux et al. 1996; Wieringa et al. 1997; Sekine et al. 2004; 3

Prevalence

of respiratory

symptoms

Wheezing

Van der Zee et al. 2000; Bjornsson et al. 1994; Viegi et al. 1991; Viegi et al. 1999;

Devereux et al. 1996; Wieringa et al. 1997; Wieringa et al. 1998; Wieringa et al. 2001;

Walraven et al. 2001; Burr et al. 2004; Sekine et al. 2004; Jedrychowski et al. 1989

Fev1 Boezen et al.. 1998; Kumar et al. 2000; Chattopadhyay et al. 2007; Sichletidis et al 2005;

Vanderjagt et al. 2004; Lubinski et al. 2005; Sekine et al. 2004; Heydarpour et al. 2007 8

Fvc Kumar et al. 2000; Chattopadhyay et al. 2007; Sichletidis et al. 2005; Vanderjagt et al. 2004;

Lubinski et al. 2005; Sekine et al. 2004; Heydarpour et al. 2007 7

Fev1/Fvc Chattopadhyay et al. 2007; Sichletidis et al. 2005; Vanderjagt et al. 2004;

Lubinski et al. 2005; Heydarpour et al. 2007 5

PEFR Kumar et al. 2000; Chattopadhyay et al. 2007; Vanderjagt et al. 2004; Lubinski et al. 2005 4

Fef25-75 Chattopadhyay et al. 2007; Sichletidis et al. 2005; Vanderjagt et al.. 2004; Heydarpour et al. 2007; 4

Lung

Function

Fef75-85 Chattopadhyay et al. 2007 1

Chronic Bron-

chitis Viegi et al. 1991; Viegi et al. 1999; Viegi et al. 2004; Kumar et al. 2000 4

Asthma

Van der Zee et al. 2000; Bjornsson et al. 1994; Viegi et al. 1991; Viegi et al. 1999; Viegi et al. 2004;

Wieringa et al. 1997; Wieringa et al.. 1998; Wieringa et al.. 2001; Walraven et al.. 2001;

Burr et al. 2004; Sekine et al. 2004

Rinithis Sichletidis et al. 2005; Viegi et al. 1991; Burr et al. 2004; Kumar et al.. 2000 4

Emphisema Viegi et al. 1991; Viegi et al. 1999; Viegi et al. 2004; Wieringa et al. . 2001 4

Prevalence of

respiratory

disease

Drug use for

asthma

Van der Zee et al. 2000; Devereux et al. 1996; Wieringa et al. 1998;

Wieringa et al. 2001; Burr et al. 2004 5

Table 2. Statistical Analysis for variables.

Indici della meta-analisi

Classe Variabile CampioneRisultato

P I2 % ES

Cough GE: 11389

GC: 16009 Increased in the exposed groupZ = 3.556

P = 0.000 72.890 OR 1.277

[1.116; 1.461]

Phlegm GE: 4971

GC: 7837 Increased in the exposed groupZ = 2.030

P = 0.042 66.369 OR 1.239

[1.007; 1.524]

Dyspnea GE: 3499

GC: 5590 NS Z = –0.144

P = 0.885 99.985 OR 0,948

[0.459; 1.959]

Short breath/breathlessness GE: 2834

GC: 3979 Increased in the exposed groupZ = 2.623

P = 0.009 78.948 OR 2.058

[1.200; 3.528]

Prevalence of respiratory

symptoms

Wheezing GE: 16322

GC: 21040 Increased in the exposed groupZ = 4.657

P = 0.000 82.950 OR 1,402

[1.216; 1.617]

FEV1

GE: 2282

GC: 1810 decreased in the exposed groupZ = –2.904

P = 0.004 79.272 SMD –0.282

[–0.472; 0.092]

FVC GE: 2191

GC: 1712 decreased in the exposed groupZ = –4.062

P = 0.000 21.996 WMD –0.139

[–0.206; 0.072]

FEV1/FVC GE: 2033

GC: 1536 NS Z = –1.512

P = 0.131 87.879 SMD –0.230

[–0.528; 0.068]

PEFR GE: 336

GC: 736 decreased in the exposed groupZ = –4.779

P = 0.000 0.000 SMD –0.320

[–0.452; –0.189]

Fef25-75

GE: 1883

GC: 1207 NS Z = –1.644

P = 0.100 26.788 WMD –0.064

[–0.139; 0.012]

Lung Function

Fef75-85

GE: 94

GC: 289 NS Z = –1.673

P = 0.094 46.843 WMD –0.199

–0.433; 0.034]

Chronic Bronchitis GE: 4252

GC: 7602 Increased in the exposed groupZ = 4.147

P = 0.000 52.391 OR 2.256

[1.536; 3.313]

Prevalence of respiratory

disease

Asthma GE: 15643

GC: 21176 Increased in the exposed groupZ = 3.864

P = 0.000 77.540 OR 1.573

[1.250; 1.958]

Metanalysis: Respiratory Effects in the General Population Exposed to Urban Pollution

977

Rinithis GE: 2862

GC: 4630 Increased in the exposed groupZ = 2.123

P = 0.034 97.217 OR 2.824

[1.083; 7.361]

Emphisema GE: 5639

GC: 9390 Increased in the exposed groupZ = 5.057

P = 0.000 78.247 OR 2.976

[1.950; 4.541]

Drug use for asthma GE: 6307

GC: 6903 NS Z = 1.474

P = 0.140 60.016 OR 1.201

[0.941; 1.533]

GE: group of exposed; GC: gruop of control; NS: Not Significant; P: Probability; I2: Inconsistence Index; ES: Effect Size; SMD: Standardized Mean Difference; WMD: Weighted Mean

Difference; OR: Odds Ratio.

Table 3. Statistical Analysis for class.

Indici della meta-analisi

Classe Campione Risultato

P I2 % ES

Prevalence of respiratory symptoms GE: 16,509

GC: 21,319 High in the exposed group Z = 5.26

P = 0.00 85.23 OR 1.30

[1.17; 1.43]

Lung Function GE: 2282

GC: 1810 Low in the exposed group Z = –4.08

P = 0.00 85.58 SMD –0.21

[–0.31; –0.11]

Prevalence of respiratory disease GE: 20,009

GC: 24,419 High in the exposed group Z = 4.89

P = 0.00 92.16 OR 1.66

[1.35; 2.04]

GE: group of exposed; GC: group of controls; P: Probability; I2: Inconsistence Index; ES: Effect Size; SMD: Standardized Mean Difference; OR: Odds Ratio.

assessment of the effects on the respiratory systems and

of the factors related to the onset of lung disease.

The following variables contained data expressed as

means and standard deviations:

 FEV1

 FVC

 PEFR

 FEV1/FVC (Tiffeneau index)

 FEF 25 - 75

 FEF 75 - 85

The following variables gave data expressed in fre-

quency:

 cough

 sputum

 wheezing

 dyspnea

 shortness of breath / breathlessness

 Chronic bronchitis

 Asthma

 emphysema

 use of medications for asthma

5. Statistical Analysis

The Effect Size (ES) is a value that expresses the

magnitude of the association strength between two

variables and was used to express the result of our meta-

analysis.

The confidence interval of the effect size was also

calculated, that expresses the accuracy with which the

effect size was estimated in our study.

In our study the confidence interval corresponds to

95% of the observations, P value was set equal to P <

0.05. The P value that is necessarily correlated to the con-

fidence interval allows to express the significance of the

ES.

When studies reported data expressed as mean and

standard deviation, the ES was expressed in Standardized

Mean Difference or in Weighted Mean Difference de-

pending on the value of the Index of Inconsistency (I2).

The Inconsistency Index was used as a measure of het-

erogeneity. In the systematic review, the heterogeneity

relates to the variability or the difference among the stud-

ies on the evaluation of the effects.

With the I2, we calculated the percentage of variance

due to real heterogeneity rather than to the blind chance.

If the I2 value is near to the zero, the observed variance

is referable to the blind chance while if the I2 value is

high the variance is referable to different factors that

must be better investigated.

The calculation of heterogeneity was used for the

choice of the statistical model to calculate the ES.

In the presence of a high Inconsistency Index (I2 >

50%), the ES was evaluated with the Random Effects

Model (REM) that is a statistical model in which the

confidence interval is influenced by the sampling error

internal to the study and by the variability among the

studies included in the meta-analysis. In this case, the

REM is more robust because it provides wider confi-

dence intervals than those obtained from another model

which the Fixed Effects Model (FEM). The quantifica-

tion of the ES was calculated with the Standardized

Mean Difference (SMD) that shows the relationship be-

tween the difference of two averages and an estimator of

standard deviation inside the group.

Without a high inconsistency between the studies (I2 <

50%), the ES was calculated with the FEM. In this model,

only the variations inside the study can influence the

confidence interval. So, the quantification of the ES is

made with the Weighted Mean Difference (WMD),

which allows to combine the measures of a continue

Metanalysis: Respiratory Effects in the General Population Exposed to Urban Pollution

978

scale when average, standard deviation and numerosity

of the sample are known parameters. The importance that

is given to each study is determined by the precision of

the estimator of the effect provided that all studies have

measured the variable with the same rating scale. A dif-

ference of 0.0 showed lack of difference among studied

groups, for the measures of ES based on the differences

(i.e. SMD and WMD).The ES was expressed in terms of

Odds Ratio (OR), when the studies reported data ex-

pressed in frequency.

As described above, in the presence of a high degree

of heterogeneity (I2 > 50%), the ES was assessed with the

Random Effects Model (REM) while in the absence of

high heterogeneity among studies (I2 < 50 %), the calcu-

lation of the ES was performed with the Fixed Effects

Model (FEM).

A ratio of 1.0 indicates no difference among the stud-

ied groups, for measures of ES based on the reports (i.e.

OR) [4].

The results are been detected on the basis of the activ-

ity of research after a convention between the University

of Rome “Sapienza” (Unit of Occupational Medicine)

and INAIL (National Institute for the Insurance against

the Accident at Work).

6. Results

From the elaboration of the data inherent to each class

we had the following results [1-26]:

 The prevalence of respiratory symptoms, evaluated in

15 studies, on a total sample of 16.509 cases and

21.319 controls, appears significantly higher in the

group of subjects exposed to urban pollution than in

the group of less exposed subjects (OR 1.30 [1.18;

1.43]) the value of heterogeneity among the studies

was I2 85.23.

 The lung function, evaluated in 8 studies, on a total

sample of 2.282 cases and 1.810 controls, appears

significantly lower in the group of less exposed sub-

jects to urban pollution than in the group of less ex-

posed subjects (SMD –0.21 [–0.31; –0.11]) the value

of heterogeneity among the studies was I2 85.58.

 The prevalence of respiratory disease, evaluated in 13

studies, on a total sample of 20.009 cases and 24.419

controls, appears significantly higher in the group of

subjects exposed to urban pollution than in the group

of less exposed subjects (OR 1.66 [1.35; 2.04]) the

value of heterogeneity among the studies was I2

92.16.

The statistical analysis of data expressed as mean and

standard deviation gave the following results (Table 2):

 The average FVC, evaluated in 7 studies, on a total

sample of 2.191 cases and 1.712 controls, appears

significantly lower in the group of subjects exposed to

urban pollution than in the group of less exposed

subjects (WMD –0.139 [–0.206; –0.072]) the value of

heterogeneity among the studies was I2 21.996 (P =

0.000).

 The average FEV1, evaluated in 8 studies, on a total

sample of 2.282 cases and 1.810 controls, appears

significantly lower in the group of subjects exposed to

urban pollution than in the group of less exposed

subjects (SMD –0.282 [–0.472; –0.092]) the value of

heterogeneity among the studies was I2 79.272 (P =

0.004).

 The PEFR average evaluated in 4 studies, on a total

sample of 336 cases and 736 controls, appears sig-

nificantly lower in the group of subjects exposed to

urban pollution than in the group of less exposed

subjects (SMD –0.320 [–0.452; –0.189]) the value of

heterogeneity among the studies was (I2 0.00; P =

0.000).

 For all other evaluated parameters (FEV1/FVC,

FEF25-75, FEF75-85) there were no statistically sig-

nificant differences in the comparison of values found

in the exposed group and in the group of less ex-

posed.

The statistical treatment of data expressed in frequency

gave the following results (Table 2):

 Prevalence of respiratory symptoms: cough (OR

1.277 [1.116 to 1.461]; I2 72.890, P 0.000), phlegm

(OR 1.239 [1.007 to 1.524]; I2 66.369, P 0.042),

wheezing (OR 1.402 [1.216 to 1.617]; I2 82.950, P

0.000), shortness of breath/breathlessness (OR 2.058

[1.200 to 3.528]; I2 78.948, P 0.009), increased sig-

nificantly in the group of subjects exposed to urban

air pollution compared to the group of less exposed;

 Prevalence of respiratory disease: chronic bronchitis

(OR 2.256 [1.536 to 3.313]; I2 52.391, P 0.000),

bronchial asthma (OR 1.573 [1.250 to 1.980]; I2

77.540, P 0.000), rhinitis (OR 2.824 [1.083 to 7.361];

I2 97.217, P 0.034) and emphysema (OR 2.976 [1.954

to 4.541]; I2 78.247, P 0.000) increased significantly

in the group of subjects exposed to urban air pollution

compared with subjects less exposed.

As to the other parameters no statistically significant

differences appeared in the comparison of the frequen-

cies found in the two groups.

7. Discussion

The results of our meta-analysis allow to confirm the

evidence of the effects of urban pollution on the respira-

tory system, although the mechanisms of action have

been clarified only in part (Committee the Environmental

and Occupational Health Assembly of the American

Thoracic Society 1996).

The effects of pollutants on the respiratory system de-

Metanalysis: Respiratory Effects in the General Population Exposed to Urban Pollution979

pend on the type of pollutant, its concentration in the

environment, on the duration of exposure and ventilatory

capacity [11].

Our results in line with other studies in the scientific

literature support the hypothesis that the reduction of

some parameters of lung function such as FVC, FEV1

and PEFR found in the general population living in urban

areas, or in areas with high pollution, could be due to

exposure to urban pollutants and depict a framework of

obstructive syndrome [12].

In one study [5], conducted in the USA, there was a

significant association between lung function and levels

of suspended particles in the non-smoking adults exam-

ined (NHANES I). The study showed that the increase of

particulate was associated with a decrease of FVC: this

association ceased approximately below 60 μg/m3 of

particulate [10].

A reduction of respiratory capacity (FVC and FEV1)

is also observed in the study of Pope III et al. 1993: in

particular a decrease of 2% of FEV 1 for rise of PM10 of

100 g/m3 in the subjects examined resulted statistically

significant, all the subjects were smokers with mild or

moderate chronic obstructive lung disease [13].

Another study [7] that must be remembered was made

in Cracovia on 1414 persons who hadn’t changed resi-

dence in the last 8 years: a faster decrease of respiratory

function was observed in persons living in an areas with

SO2 and PM10 pollution compared people living in other

areas.

An association between previous chronic exposition to

high levels of air pollution and respiratory function was

found in non-smokers living in 2 areas characterized by

different levels of pollution [16,17].

In an Italian study among subjects with BPCO and

asthma, the results of the analysis show that an increase

of environmental concentrations of PM10 and PM2,5

causes a decrease of respiratory function during the fol-

lowing 24 h - 48 h [18-20].

A Dutch study shows a reverse correlation between

FEV1 and nearness to a very busy freeway or between

FEV1 and the number of heavy vehicles in a day [8].

The availability of controlled studies in the literature is

rather small but the number of subjects studied is quite

high. Many studies [22-24] show a disparity between the

number of those who constitute the experimental group

and the size of the control group with the resulting dis-

tortion of the results.

However, the processing of the data available, grouped

by the three classes, allowed us to demonstrate an im-

pairment of the respiratory system characterized by:

1) reduction in lung function (I2 98.23);

2) increased prevalence of the class of symptoms (I2

55.65);

3) increase in respiratory disease (I2 51.31).

Among the class of respiratory symptoms, the results

on the short breath/breathlessness and wheezing were the

most sensitive.

With an ES of 2.06 and 1.40 respectively, the meta-

analysis indicates that within the population most ex-

posed, shortness of breath/breathlessness and wheezing

were observed more frequently than in individuals be-

longing to the group of less exposed.

Studies concerning the variable shortness of breath/

breathlessness and wheezing, show a low homogeneity

represented by their high value of I2 (respectively 78.95

and 82.95) [25].

Among respiratory disease, variables with a high sen-

sitivity that can be attributed to the effects of pollution

include chronic bronchitis, emphysema with an ES of

2.25 and 2.97 respectively.

The heterogeneity among the studies which analysed

for the presence of chronic bronchitis is 52.39 instead of

78.24 for the variable emphysema [9]. Among the statis-

tically significant results related to lung function the pa-

rameters FVC, FEV1 and PEFR are all reduced, indicat-

ing obstructive deficit as chronic effect in the exposed

population. The ES of the FVC and FEV1 PEFR is re-

spectively –0.14 and –0.28 –0.32 while the value of I2 is

respectively 21.99, 79.27 and zero.

The meta-analysis identified the variables that can be

used as indicators of the effects of pollution on the respi-

ratory system. Variables with low heterogeneity and high

sensitivity as the PEFR and bronchitis may be considered

useful indicators of exposure to urban pollutants [26].

The variables with high sensitivity and high heteroge-

neity such as emphysema and shortness of breath/

breathlessness should be further explored in future stud-

ies to verify their usefulness as indicators of exposure to

urban pollution.

8. Conclusions

In the light of the results is clear that the health of the

population exposed to urban pollution must necessarily

include a careful evaluation of the respiratory system

through targeted surveys to the variables mentioned

above with high sensitivity.

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