Characteristics of COPD in never-smokers and ever-smokers in the general population: results from the CanCOLD study

Abstract

Background There is limited data on the risk factors and phenotypical characteristics associated with spirometrically confirmed COPD in never-smokers in the general population.
Aims To compare the characteristics associated with COPD by gender and by severity of airway obstruction in never-smokers and in ever-smokers.
Method We analysed the data from 5176 adults aged 40 years and older who participated in the initial cross-sectional phase of the population-based, prospective, multisite Canadian Cohort of Obstructive Lung Disease study. Never-smokers were defined as those with a lifetime exposure of <1/20 pack year. Logistic regressions were constructed to evaluate associations for ‘mild’ and ‘moderate-severe’ COPD defined by FEV1/FVC <5th centile (lower limits of normal). Analyses were performed using SAS V.9.1 (SAS Institute, Cary, North Carolina, USA).
Results The prevalence of COPD (FEV1/FVC<lower limits of normal) in never-smokers was 6.4%, constituting 27% of all COPD subjects. The common independent predictors of COPD in never-smokers and ever-smokers were older age, self reported asthma and lower education. In never-smokers a history of hospitalisation in childhood for respiratory illness was discriminative, while exposure to passive smoke and biomass fuel for heating were discriminative for women. COPD in never-smokers and ever-smokers was characterised by increased respiratory symptoms, ‘respiratory exacerbation’ events and increased residual volume/total lung capacity, but only smokers had reduced DLCO/Va and emphysema on chest CT scans.
Conclusions The study confirmed the substantial burden of COPD among never-smokers, defined the common and gender-specific risk factors for COPD in never-smokers and provided early insight into potential phenotypical differences in COPD between lifelong never-smokers and ever-smokers.
Trial registration number NCT00920348 (ClinicalTrials.gov); study ID number: IRO-93326.

Full text

ORIGINAL ARTICLE
Characteristics of COPD in never-smokers
and ever-smokers in the general population:
results from the CanCOLD study
W C Tan,
1
D D Sin,
1
J Bourbeau,
2
P Hernandez,
3
K R Chapman,
4
R Cowie,
5
J M FitzGerald,
6
D D Marciniuk,
7
F Maltais,
8
A S Buist,
9
J Road,
6
J C Hogg,
1
M Kirby,
1
H Coxson,
1
C Hague,
10
J Leipsic,
10
DEO’Donnell,
11
S D Aaron,
12
CanCOLD Collaborative Research Group
▸Additional material is
published online only. To view
please visit the journal online
(http://dx.doi.org/10.1136/
thoraxjnl-2015-206938).
For numbered affiliations see
end of article.
Correspondence to
Dr Wan C Tan, UBC James
Hogg Research Centre,
Providence Heart+Lung
Institute, University of British
Columbia, St Paul’s Hospital,
Rm 166, 1081 Burrard Street,
Vancouver, British Columbia,
Canada V6Z 1Y6;
wan.tan@hli.ubc.ca
Received 13 February 2015
Revised 8 May 2015
Accepted 21 May 2015
To cite: Tan WC, Sin DD,
Bourbeau J, et al.Thorax
Published Online First:
[please include Day Month
Year] doi:10.1136/thoraxjnl-
2015-206938
ABSTRACT
Background There is limited data on the risk factors
and phenotypical characteristics associated with
spirometrically confirmed COPD in never-smokers in the
general population.
Aims To compare the characteristics associated with
COPD by gender and by severity of airway obstruction in
never-smokers and in ever-smokers.
Method We analysed the data from 5176 adults aged
40 years and older who participated in the initial cross-
sectional phase of the population-based, prospective,
multisite Canadian Cohort of Obstructive Lung Disease
study. Never-smokers were defined as those with a
lifetime exposure of <1/20 pack year. Logistic
regressions were constructed to evaluate associations for
‘mild’and ‘moderate-severe’COPD defined by FEV
1
/FVC
<5th centile (lower limits of normal). Analyses were
performed using SAS V.9.1 (SAS Institute, Cary, North
Carolina, USA).
Results The prevalence of COPD (FEV
1
/FVC<lower
limits of normal) in never-smokers was 6.4%,
constituting 27% of all COPD subjects. The common
independent predictors of COPD in never-smokers and
ever-smokers were older age, self reported asthma and
lower education. In never-smokers a history of
hospitalisation in childhood for respiratory illness was
discriminative, while exposure to passive smoke and
biomass fuel for heating were discriminative for women.
COPD in never-smokers and ever-smokers was
characterised by increased respiratory symptoms,
‘respiratory exacerbation’events and increased residual
volume/total lung capacity, but only smokers had
reduced DLCO/Va and emphysema on chest CT scans.
Conclusions The study confirmed the substantial
burden of COPD among never-smokers, defined the
common and gender-specific risk factors for COPD in
never-smokers and provided early insight into potential
phenotypical differences in COPD between lifelong
never-smokers and ever-smokers.
Trial registration number NCT00920348
(ClinicalTrials.gov); study ID number: IRO-93326.
INTRODUCTION
The occurrence of COPD in never-smokers is not
widely appreciated,despite the fact that the relative
burden of COPD in never-smokers is high in
developing
1
and developed countries,
2
accounting
for about 30%
3–7
of all COPD in the community.
There is limited information on the risk factors asso-
ciated with spirometrically confirmed COPD in never-
smokers in the general population.
589
and more data
from population-based studies are needed.
10
Risk factor exposures may differ between
sexes.
11
In developing countries, biomass fuel
exposure has been consistently linked with chronic
bronchitis and spirometrically defined COPD in
women.
10 12
Limited data from population-based
studies suggest that there could be different clinical
and gender-related risk exposure profiles between
smoking and non-smoking COPD.
613
There is uncertainty on the clinical relevance of
COPD in never-smokers because of the lack of clin-
ical data on never-smokers with irreversible airflow
limitation in comparison to that in smokers. Such
uncertainty raises doubt about whether irreversible
airflow limitation in ever-smokers and never-
smokers should be managed differently.
10 14
Key messages
What is the key question?
▸What are the clinical characteristics and
associated factors for COPD in never-smokers in
the general population and are they different
from those of COPD in ever-smokers?
What is the bottom line?
▸The results clearly showed that the COPD in
never-smokers forms a substantial burden in
the population; that there are gender-specific
differences in never smokers with COPD and
that there are physiological and radiographic
differences between COPD in never-smokers
compared with that in ever-smokers.
Why read on?
▸The study highlights the substantial burden of
COPD among never-smokers and provides
additional data on the sex differences profiling
never-smokers COPD and early insight into
phenotypical differences for COPD in lifelong
never-smokers and ever-smokers.
Tan WC, et al.Thorax 2015;0:1–8. doi:10.1136/thoraxjnl-2015-206938 1
Chronic obstructive pulmonary disease
Thorax Online First, published on June 5, 2015 as 10.1136/thoraxjnl-2015-206938
Copyright Article author (or their employer) 2015. Produced by BMJ Publishing Group Ltd (& BTS) under licence.
group.bmj.com on June 6, 2015 - Published by http://thorax.bmj.com/Downloaded from

Whether never-smokers with COPD share the phenotypes as
their smoking counterparts is unclear. Few studies performed
simultaneous evaluation of COPD in never-smokers and ever-
smokers in the same study.
67
Such evaluation would facilitate
comparison of COPD in never-smokers with COPD in ever-
smokers
10
and provide insight into potential phenotypical
differences in tobacco and non-tobacco related COPD at the
population level. Hence, population-based studies using spirom-
etry, including gender and systematic comparison of never-
smokers and ever-smokers are needed to address this gap in our
understanding of COPD in never-smokers.
10
In this study, we analysed the data from the initial cross-sectional
phase of the population-based, prospective Canadian Cohort of
Obstructive Lung disease (CanCOLD) study. The primary object-
ive was to determine the characteristics associated with COPD
defined by postbronchodilator spirometry in never-smokers and
ever-smokers in the general population. As a secondary objective,
in a subgroup of the population cohort who had additional radio-
logical and physiological data, we compared respiratory symptoms
and exacerbations, plethysmographic lung volumes and DLCO
abnormalities, and prevalence of emphysema on CT in never-
smokers and ever-smokers, with and without COPD.
MATERIALS AND METHODS
Study population
The data from 5176 people from the general population, aged
40 years and older were evaluated. Data were collected between
August 2005 and May 2009, in a large cross-sectional multisite,
population-based study on lung health, which constituted the
cross-sectional phase of the prospective longitudinal CanCOLD
study. The study was initiated in Vancouver as part of the Burden
of Obstructive Lung Disease (BOLD) study
15
and then completed
in eight other Canadian cities. The sampling strategy and study
protocol of the baseline cross-sectional part of the study were the
same as that used in the international BOLD initiative, the full
details of which have been published elsewhere.
15 16
Briefly, random samples were drawn from census data from
Statistics Canada (Survey and Analysis Section; Victoria, Canada)
and comprised of non-institutionalised adults, aged 40 years and
older in nine urban cities across Canada (Vancouver, Montreal,
Toronto, Halifax, Calgary, Quebec City, Kingston, Saskatoon and
Ottawa). Recruitment was conducted by Nordic Research Group
(NRG) Research group (Vancouver, Canada) by random tele-
phone digit dialling to identify eligible individuals
15 16
who were
invited to attend a clinic visit to complete interviewer-
administered respiratory questionnaires and to perform pre-
bronchodilator and postbronchodilator spirometry.
15 16
The
mean clinic visit participation rate was 74% (range 63–87%).
16
Definitions
Ever-smokers and never-smokers
The whole cohort was stratified into ever-smokers and never-
smokers. Never-smokers were defined as individuals who had
not smoked in their lifetime, more than 1 cigarette per day for
1 year (<1/20 pack years).
15
COPD and Non-COPD subgroups
Two spirometric definitions for COPD were used: (A) ‘COPD
definition derived from the Global Initiative for Chronic
Obstructive Lung Disease (GOLD)
17
based on postbronchodila-
tor FEV
1
/FVC <0.70; and (B) the alternative definition for
COPD as FEV
1
/FVC <5th centile (lower limits of normal, LLN).
Ever-smokers and never-smokers were stratified into
‘Non-COPD’and ‘COPD’subgroups defined by FEV
1
/FVC
<0.7 (GOLD criteria) or by FEV
1
/FVC<LLN, for comparison of
the associated factors for COPD. Severity of COPD subgroups
was further defined as mild (FEV
1
%pred ≥80%) or moderate-
severe (FEV
1
%pred <80%). The reference equations derived
from Hankinson et al
18
were used in the spirometric definitions.
Exposures
Passive smoking at home was evaluated by asking the question:
“has anyone living in your home (besides yourself) smoked a cig-
arette, pipe, or cigar in your home during the past two weeks.”
Biomass fuel exposure was defined as a lifetime exposure of
10 years or greater from the use of indoor fire using (1) coal or
coke; (2) wood, crop residues or dung as the primary means of
cooking or heating (details in online supplementary file).
Physiological and CT measurements
A subset of individuals who had CT scans of thorax and full lung
function tests were assessed to determine the frequencies of
emphysema, chronic respiratory symptoms and exacerbations
and physiological measures of lung volumes and transfer factor
(DLCO/Va).
19
We had information on respiratory symptoms and
exacerbations in 4890 subjects (2292 never-smokers and 2598
ever-smokers); pulmonary function testings in 977 subjects (456
never-smokers and 521 ever-smokers) and CT scans in 835 sub-
jects (394 never-smokers and 441 ever-smokers). The grading of
CT scans was done by two senior radiologists independently and
blinded to the COPD or smoking status of subjects.Visually
defined emphysema score was computed by the summation of
the scores of the upper, middle and lower zones of right and left
lungs on the CT scan using the method described in the
COPDGene study.
20
All participants gave written informed consent.
Statistical analysis
All statistical analyses were performed using SAS V.9.1 (SAS
Institute, Cary, North Carolina, USA). A two-sided p<0.05,
with adjustment for multiple comparisons using the Holm-
Bonferroni correction was considered statistically significant.
Descriptive statistics are shown as counts and percentages for
categorical data and means and SDs for continuous variables,
unless otherwise stated.
Comparisons of variables between ever-smokers and never-
smokers and between ‘non-COPD’and ‘COPD’were performed
using Kruskal-Wallis test and χ
2
test for continuous variables and
categorical variables, respectively. Unweighted and weighted
prevalences of COPD were calculated by smoking status for
men and women.
To address the determinants for COPD, multivariable logistic
regression models (parsimonious and full ) were constructed to
evaluate associations in all never-smokers and all ever-smokers;
separately by sex and by COPD severity qualified by post- bron-
chodilator FEV
1
% predicted ≥80% and <80%. Covariates in
the model included: age, body mass index (BMI) and years of
education; exposure to organic dust, inorganic dust, biomass
fuel (cooking or heating), environmental/passive tobacco smoke;
history of childhood hospitalisation; cardiovascular comorbidity
(heart disease, hypertension or diabetes); asthma and TB (details
in online supplementary file).
RESULTS
Of 5176 participants, 4893 (94%) individuals had spirometric
measurements, which satisfied the American Thoracic Society
(ATS) acceptability and repeatability criteria
21
and were used in
the analysis in the study.
2 Tan WC, et al.Thorax 2015;0:1–8. doi:10.1136/thoraxjnl-2015-206938
Chronic obstructive pulmonary disease
group.bmj.com on June 6, 2015 - Published by http://thorax.bmj.com/Downloaded from

Characteristics of never-smokers and ever-smokers in the
study population
The study population comprised 47% never-smokers and 53%
ever-smokers.
Table 1 shows the demographic characteristics and exposure
types and use of respiratory medications in the whole cohort
stratified by smoking status. Compared with ever-smokers,
never-smokers were younger, included more women, had lower
BMI, had more years of education, had lower frequencies of
exposure to inorganic dust and noxious gases or vapours at
work, and comorbidities, but had similar frequencies of self-
reported physician diagnosis of asthma and TB, and use of
respiratory medications
Prevalence of COPD in never-smokers and
ever-smokers by sex
Never-smokers accounted for 29% of all COPD identified by
spirometry in the study.
The prevalence of airflow obstruction was 6.43% in never-
smokers and 15.28% in ever-smokers when FEV
1
/FVC <5th
centile, LLN criteria was used. Of ever-smokers with COPD,
62% had moderate-severe airflow obstruction (FEV
1
%pred
<80%) compared with 43% of never-smokers with COPD
(p<0.05).
Figure 1 shows that COPD in never-smokers was more likely
to affect women (7.4%) compared with men (5.0%)
(p<0.0322). In contrast, COPD rates among smokers were
similar for women and men.
Factors independently associated with COPD in
never-smoking men and women
Table 2 shows the adjusted OR and 95% CI from the multivari-
able logistic regression analyses for determining the ‘risk factors’
associated with COPD (defined by FEV
1
/FVC<LLN). In never-
smokers with COPD of all severity, the common independent
associations were older age and a history of asthma. For mild
COPD, fewer years of education was a discriminative factor in
men and passive smoking at home and cardiovascular comorbid-
ities (heart disease or systemic hypertension or diabetes) were
discriminative factors in women. For moderate and severe
Table 1 Demographic, exposure and clinical characteristics of the study population by smoking status (never-smokers vs ever-smokers)
Never-smokers
n=2295 Per cent
Ever-smokers
n=2598 Per cent Adjusted p value*
Sex (men) 891 38.82 1205 46.38 0.0023
Ethnicity (Caucasian) 2019 88.0 2456 94.5 0.0022
Age, year, mean±SD 55.69±11.17 –58.18±11.03 –0.0021
Age, years 0.0020
40–49 702 30.59 672 25.87 –
50–59 750 32.68 811 31.22 –
60–69 501 21.83 674 25.94 –
70+ 342 14.90 441 16.97 –
BMI, kg/m
2
, mean±SD 27.51±5.66 –28.27±5.96 –0.0019
Education, year, mean±SD 16.06±3.51 –14.81±3.49 –0.0018
Pack years >20 ––1231 47.38 –
Exposures
Organic dust 202 8.80 243 9.35 1.0000
Inorganic dust 46 2.00 112 4.31 0.0017
Gases/vapours 89 3.88 155 5.97 0.0112
Biomass fuel†
≥10 years cooking 196 12.03 225 13.16 1.0000
≥10 years heating 246 15.10 312 18.25 0.1639
Passive smoking at home 106 4.62 361 13.90 0.0016
Childhood hospitalisation for respiratory illness 111 4.84 173 6.66 0.0871
Comorbidities, ever
HD/HT/DM‡728 31.72 999 38.45 0.0015
Asthma 369 16.08 424 16.32 1.0000
TB 31 1.35 35 1.35 0.9914
Use of respiratory medications 746 32.6 855 32.9 1.0000
Prescribed medication 416 18.2 534 20.6 0.149
Bronchodilator 272 11.9 373 14.4 0.1224
Inhaled steroid 332 14.5 428 16.5 0.4432
Oral steroid 10 0.4 10 0.4 1.0000
Anti-inflammatory (other) 16 0.7 21 0.8 1.0000
OTC§ medication 306 13.4 290 11.2 0.1341
Data are mean±SD or count and %. p Values of tests between never-smokers and ever-smokers; Kruskal-Wallis test (without assumption of normal distribution of data) and χ
2
test are
used for continuous variables and categorical variables, respectively.
*p Values adjusted after Holm-Bonferroni correction.
†Calculated based on six sites with available biomass data.
‡Heart disease, systemic hypertension or diabetes.
§Includes antihistamines, decongestants and antitussives.
BMI, body mass index; HD/HT/DM, heart disease/ systemic hypertension/diabetes mellitus.
Tan WC, et al.Thorax 2015;0:1–8. doi:10.1136/thoraxjnl-2015-206938 3
Chronic obstructive pulmonary disease
group.bmj.com on June 6, 2015 - Published by http://thorax.bmj.com/Downloaded from

COPD, the additional common ‘risk factor’was childhood hos-
pitalisation for respiratory disease, while exposure to biomass
fuel used for heating purposes for at least 10 years was a dis-
criminative factor in women. Using the alternative definition for
COPD (FEV
1
/FVC <0.7) and grading of mild (FEV
1
%pred
≥80%) and moderate-severe (FEV
1
%pred <80%), the results
(not shown) remained unchanged.
Factors associated with COPD in ever-smokers
There was no sex-related difference in risk factors for COPD in
ever-smokers. Table 3 shows that the independently associated
factors for COPD of all grades of severity (mild, moderate and
severe) in ever-smokers were older age, pack years >20 and a
self-reported history of physician diagnosed asthma. Low BMI
was an associated factor for mild COPD while fewer years of
education was an associated factor for moderate and severe
COPD.
Comparison of clinical, physiological and structural
characteristics of COPD in never-smokers with COPD in
ever-smokers
Figures 2–4show the comparisons of COPD versus non-COPD
for (A) respiratory symptoms including exacerbations and self-
reported ever asthma (figure 2); (B) respiratory physiology
(figure 3); and (C) visually defined emphysema, bronchiolitis
and bronchiectasis on CT scans for never-smokers and ever-
smokers (figure 4). Regardless of smoking status, individuals
with COPD compared with those without COPD had more fre-
quent respiratory symptoms of chronic cough, chronic phlegm,
dyspnoea on exertion, wheeze in the last year; more likely to
have previous experiences of respiratory exacerbations, and
increased residual volume/total lung capacity ratio. Ever-
smokers with COPD had increased total lung capacity, reduced
transfer factor (DLCO/Va) and increased frequency of visually
defined emphysema on CT scan compared with never-smokers
with COPD. The prevalence of radiological bronchiectasis on
CT was not significantly increased in COPD in smokers and
non-smokers (details in online supplementary table S4).
DISCUSSION
We have found similarities and differences in the characteristics
of COPD between never-smokers and ever-smokers. First, we
showed in this population study that never-smokers accounted
for nearly 30% of the total burden of COPD in the community
and that never-smokers with COPD were predominantly
women. Second, the factors independently associated with
COPD in never-smokers for men and women included increas-
ing age, a diagnosis of asthma and severe childhood respiratory
disease while passive smoking and exposure to biomass fuel
heating were independent factors for COPD in women. No
gender-specific difference in associated factors for COPD was
found in ever-smokers, in whom COPD was similarly linked
with increasing age, a diagnosis of asthma, severe childhood
respiratory disease, but additionally, with increasing lifetime
exposure (pack years) to cigarette smoking. Finally, in a prelim-
inary evaluation of a subset of the cohort to assess phenotypical
differences in COPD, we showed that COPD in never-smokers
and ever-smokers had a similar respiratory symptoms profile but
were different in radiological and physiological presentations.
The finding in this study that nearly 30% of all people diag-
nosed with COPD have never smoked was consistent with
reported proportions of 25–30% in USA,
5
Europe
47
and
China.
16
As 47% of our study population were never-smokers,
and 10% of these had COPD, this would translate into an
overall population prevalence of 4.7% or 1.08 million indivi-
duals with airway obstruction in a population of about 23
million Canadians aged 40 years or older. Notably, about 70%
Figure 1 Weighted prevalence (%) of COPD (FEV
1
/FVC<LLN) by sex,
in never-smokers and ever-smokers. Pale column=men, dark
column=women. LLN, lower limits of normal.
Table 2 Adjusted OR (aOR) for independent predictors associated with risk of different severity of COPD defined by lower limits of normal in
male and female never-smokers
Variables
COPD mild COPD moderate-severe
All Men Women All Men Women
Age, +70 years (vs 40–49 years) 2.19* (1.15 to 4.16) 2.50 (0.77 to 8.16) 2.28* (1.02 to 5.06) 4.46* (1.84 to 10.8) 6.09* (1.14 to 35.4) 3.54* (1.23 to 10.1)
Education (# years) 0.98 (0.92 to 1.04) 0.88* (0.78 to 0.99) 1.02 (0.95 to 1.11) 0.95 (0.88 to 1.02) 0.96 (0.83 to 1.10) 0.94 (0.86 to 1.03)
Biomass, ≥10 years heating
(yes/no)†
0.88 (0.39 to 1.96) 2.09 (0.59 to 7.44) 0.62 (0.21 to 1.82) 2.26 (0.93 to 5.52) 0.44 (0.08 to 2.42) 3.58* (1.42 to 9.01)
Passive smoking (yes/no) 2.18 (0.99 to 4.75) 1.33 (0.26 to 6.72) 2.60* (1.05 to 6.43) 1.25 (0.42 to 3.73) 0.69 (0.08 to 6.21) 1.65 (0.46 to 5.88)
Childhood hospitalisation for
respiratory illness (yes/no)
1.57 (0.68 to 3.62) 2.95 (0.84 to 10.4) 1.18 (0.35 to 4.00) 4.80* (2.43 to 9.46) 10.1* (3.71 to 27.5) 2.24 (0.73 to 6.84)
HD/HT/DM‡(yes/no) 0.72 (0.43 to 1.21) 1.55 (0.61 to 3.95) 0.51* (0.26 to 0.98) 1.11 (0.63 to 1.94) 1.48 (0.57 to 3.90) 1.07 (0.53 to 2.16)
Asthma (yes/no) 2.23* (1.36 to 3.66) 3.39* (1.25 to 9.21) 2.14* (1.20 to 3.82) 4.94* (2.94 to 8.30) 7.34* (3.01 to 17.9) 3.89* (2.02 to 7.50)
Data are aORs and 95% CI. Adjustment made for all other covariates in model: BMI, exposure to organic dust, inorganic dust, gases/vapours, biomass cooking ≥10 years and TB. Plus
sex (for ‘all’cohorts).
*Significant at 5% level (all variables shown in online supplementary table X2).
†Calculated based on six sites with available biomass data.
‡Heart disease, systemic hypertension or diabetes.
BMI, body mass index; HD/HT/DM, heart disease/ systemic hypertension/diabetes mellitus.
4 Tan WC, et al.Thorax 2015;0:1–8. doi:10.1136/thoraxjnl-2015-206938
Chronic obstructive pulmonary disease
group.bmj.com on June 6, 2015 - Published by http://thorax.bmj.com/Downloaded from

were women, suggesting that women could be more susceptible
to non-smoking risk factors associated with COPD.
11 22
We did
not observe this gender distribution in COPD for ever-smokers,
conceivably due to the overriding effect of tobacco smoke
exposure in the causation of COPD.
The finding of sexual dimorphism in risk factors for COPD is
intriguing. A positive history of environmental tobacco smoke
exposure (passive smoking) and prolonged (>10 years) expos-
ure to biomass fuels combustion for heating were factors inde-
pendently associated with COPD in women. Biomass fuel
combustion had been clearly linked with the occurrence of
COPD in women in developing countries such as India
2
and
China
1
but to our knowledge had not been reported in the
developed countries of North America or Western Europe. Our
finding that exposure to biomass fuel combustion was related to
moderate and severe COPD in Canada cautioned against the
general assumption that the risk of biomass fuel exposure was
not a relevant risk factor for COPD among women in devel-
oped countries.
23 24
However, it is unclear what biomass
exposure represents in Canada, where the exposure frequencies
of 11–14% seem to be higher than that (5%) quoted for devel-
oped countries.
25
Conceivably it could be a surrogate for
poverty or social economic status,
12
or could be due to behav-
ioural, environmental and lifestyle differences between men and
women though differences in biological or genetic predispos-
ition could not be excluded.
11 22 26
Further clarification requires
studies on detailed and seasonal household air quality data and
longitudinal follow-up data.
A pivotal finding in this study is that a history of asthma is the
most consistent independently associated factor for COPD
regardless of smoking status. Long-standing asthma and the risk
for COPD as defined by the presence of non-fully reversible
chronic airway obstruction has been well documented in
smokers and never-smokers.
10
Individuals with chronic asthma
have a greater than normal rate of decline in lung function with
age, further magnified by presence of smoking.
24 27
The find-
ings in this study that self-reported concurrent doctor-diagnosis
of asthma occurred in 36% of all COPD in never-smokers and
Table 3 Adjusted OR (aOR) for independent predictors associated with risk of different severity of COPD defined by lower limits of normal in
male and female ever-smokers
Variables
COPD mild COPD moderate-severe
All Men Women All Men Women
Age, +70 years (vs 40–49
years)
3.01* (1.66 to 5.46) 4.19* (1.75 to 10.0) 2.23 (0.96 to 5.21) 11.58* (6.58 to 20.4) 11.27* (5.01 to 25.4) 12.64* (5.48 to 29.2)
BMI (kg/m
2
) 0.95* (0.92 to 0.98) 0.94 (0.89 to 0.99) 0.95* (0.91 to 0.99) 0.99 (0.96 to 1.01) 0.97 (0.93 to 1.02) 0.99 (0.96 to 1.02)
Current smoking (vs former) 1.73* (1.15 to 2.62) 2.52* (1.34 to 4.71) 1.33 (0.76 to 2.32) 2.89* (2.04 to 4.10) 3.61* (2.04 to 6.38) 2.53* (1.61 to 3.98)
Pack years 20+ (vs 0–10) 2.52* (1.53 to 4.14) 2.58* (1.18 to 5.61) 2.52* (1.31 to 4.83) 3.57* (2.26 to 5.62) 2.82* (1.43 to 5.58) 4.16* (2.24 to 7.73)
Education (# years) 1.00 (0.96 to 1.05) 1.02 (0.95 to 1.10) 0.98 (0.91 to 1.05) 0.94* (0.90 to 0.98) 0.94* (0.86 to 0.99) 0.93* (0.88 to 0.99)
Asthma (yes/no) 2.51* (1.67 to 3.76) 2.74* (1.41 to 5.33) 2.25* (1.33 to 3.82) 3.82* (2.72 to 5.35) 4.58* (2.64 to 7.95) 3.22* (2.08 to 4.96)
Data are aORs and 95% CI. Adjustment made for all other covariates in the table plus sex ( for ‘all’cohorts), exposures to organic dust, inorganic dust, gases/vapours, biomass cooking
≥10 years, biomass heating ≥10 years and childhood hospitalisation for respiratory illness, HD/HT/DM and tuberculosis.
*Significant on 5% level (all variables shown in online supplementary table X3).
†Calculated based on six sites with available biomass data.
BMI, body mass index; HD/HT/DM, heart disease/ systemic hypertension/diabetes mellitus.
Figure 2 Comparison of the
proportion (%) of non-COPD and
COPD subgroups who had respiratory
symptoms (dyspnoea, chronic cough,
chronic phlegm, ever-wheeze,
exacerbation), history of exacerbations
and ever-asthma in 2292
never-smokers (2131 non-COPD (grey
column) and 161 COPD (black
column)) (upper part of figure); and in
2598 ever-smokers (2202 non-COPD
(grey column) and 396 COPD (black
column)) (lower part of figure). An
exacerbation was defined as ‘a period
of worsening of breathing problems
that got so bad that it interfered with
usual daily activities or caused the
individual to miss work’. *Proportion
(%) in ever-smoking COPD significantly
greater than that in never-smoking
COPD (additional details in online
supplementary table S4).
Tan WC, et al.Thorax 2015;0:1–8. doi:10.1136/thoraxjnl-2015-206938 5
Chronic obstructive pulmonary disease
group.bmj.com on June 6, 2015 - Published by http://thorax.bmj.com/Downloaded from

30% of COPD in ever-smokers, are consistent with published
proportions of between 15% and 55% of patients with COPD,
a combination which could alternatively be labelled as the
‘asthma-COPD overlap syndrome’.
17
In our study population, a history of childhood hospitalisa-
tion for respiratory illness was also a significant predictor of
COPD irrespective of smoking status, presumably through the
negative effect on lung function described in several studies
which found an adverse association between early childhood
lung infections and FEV
1
.
17
Such childhood ‘disadvantages’
which collectively could also include maternal smoking during
childhood, poverty and low socioeconomic status, might be as
important as heavy smoking in predicting lung function and
increasing the individual’s risk of developing COPD.
28
Finally, the paucity of phenotypical data in never-smokers
with chronic airflow obstruction had long cast doubt on aligning
COPD in never-smokers with COPD in ever- smokers.
10 14
In
the Copenhagen General Population Study on outcomes of
COPD, Thomsen et al
29
reported increased risk of respiratory
hospitalisations but not of total mortality for never-smoking
individuals with COPD compared with smokers with COPD. To
our knowledge, physiological and CT characteristics of COPD
in never-smokers versus ever-smokers from the general popula-
tion had not been systematically studied. In a preliminary com-
parative analysis of clinical variables, respiratory physiology and
visual scores from multiple detector computed tomography scan
of the lungs in individuals with and without COPD in never-
smokers and ever-smokers, we found that there were phenotyp-
ical differences between COPD in never-smokers and ever-
smokers in the general population. It is intriguing that respira-
tory symptoms such as chronic cough, chronic phlegm and
wheeze and exertional dyspnoea are features of COPD regard-
less of smoking status though more frequent in ever-smokers.
The burden of respiratory exacerbations, an outcome
29
and a
phenotypical feature for COPD,
30–32
was also equally prevalent
in ever-smokers and never-smokers with COPD.
The key differences appeared to be physiological and radio-
logical. Although never-smokers and ever-smokers with COPD
had lung hyperinflation and air trapping, never-smokers with
COPD were less likely to have emphysema on CT scan and
hence by default labelled as ‘airway predominant phenotype’
20
compared with smokers with COPD who were more likely to
have a reduced diffusing capacity and emphysema, hence
‘emphysema predominant phenotype’. These initial findings
provide some insight into potential phenotypical differences
31 33
but should be interpreted with caution and await validation
from longitudinal data of the study.
Limitations
There are potential limitations in this study. First, the ideal def-
inition for COPD remains controversial.
34 35
In this analysis, we
Figure 3 Comparison of respiratory physiology measurements
residual volume/total lung capacity (%), functional residual capacity
(FRC) (litres) and DLCO/Va (mL/min/mm Hg/l) in 456 never-smokers
(346 non-COPD (grey column) and 110 COPD (black column)) (upper
part of figure)); and in 521 ever-smokers (312 non-COPD (grey column)
and 209 COPD (black column)) (lower part of figure). *Measurements
in ever-smoking COPD significantly different from that in never-smoking
COPD (additional details in online supplementary table S4).
Figure 4 Comparison of thoracic CT
scan findings: the proportion (%) of
non-COPD and COPD subgroups with
presence of visually defined
emphysema, bronchiolitis and
bronchiectasis in 394 never-smokers
(308 non-COPD (grey column), 86
COPD (black column)) (upper part of
figure); and in 441 ever-smokers (273
non-COPD (grey column) and 168
COPD (black column)) (lower part of
figure). *Proportion (%) in
ever-smoking COPD significantly
greater than that in never-smoking
COPD (additional details in online
supplementary table S4).
6 Tan WC, et al.Thorax 2015;0:1–8. doi:10.1136/thoraxjnl-2015-206938
Chronic obstructive pulmonary disease
group.bmj.com on June 6, 2015 - Published by http://thorax.bmj.com/Downloaded from

had used two spirometric definitions of airflow obstruction as
study definitions of COPD, namely the GOLD definition: and
the alternative definition, (LLN), but chose to present results
from the LLN definition. COPD disease severity was assumed in
each case by the level of FEV
1
% predicted.
835
Another limita-
tion is that, in our analysis, a doctor diagnosis of asthma was
self-reported rather than from health records and hence could
be affected by recall bias. We did not exclude individuals with
asthma from the analysis as asthma was equally prevalent in
ever-smokers and never-smokers. Hence, some of the patients
we were labelling as COPD may have had fixed airflow obstruc-
tion and remodelling related to long-standing asthma, and some
may have had poorly controlled asthma which was not com-
pletely reversed with bronchodilators. Another caveat is the
weak definition of passive smoking. Lastly, only cross-sectional
data were used in the analysis.Hence these findings should be
interpreted with caution as confirmation would require data
from the longitudinal phase of the study.
CONCLUSION
In summary, the study confirmed the substantial burden of
COPD among never-smokers, defined the common and gender-
specific risk factors for COPD in never-smokers and provided
early insight into potential phenotypical differences in COPD
between lifelong never-smokers and ever-smokers. The establish-
ment of phenotypical differences for COPD in never-smokers
and ever-smokers could provide clearer outcomes needed for
better COPD management and for clinical trials to evaluate
novel treatments for COPD.
Author affiliations
1
University of British Columbia, Heart Lung Innovation, Vancouver, British Columbia,
Canada
2
Respiratory Epidemiology and Clinical Research Unit, Montreal Chest Institute,
McGill University Health Centre, McGill University, Montréal, Quebec, Canada
3
Department of Medicine, QEII Health Sciences Centre, Dalhousie University, Halifax,
Nova Scotia, Canada
4
Department of Respiratory Medicine, University of Toronto, Toronto, Ontario,
Canada
5
Departments of Medicine and Community Health Sciences, University of Calgary,
Calgary, Alberta, Canada
6
Department of Respiratory Medicine, University of British Columbia, Vancouver,
British Columbia, Canada
7
Department of Respiratory Medicine, University of Saskatchewan, Saskatoon,
Saskatchewan, Canada
8
Centre de Pneumologie de l’Hopital Laval, Respirology, Quebec City, Quebec,
Canada.
9
Oregon Health Sciences University, Portland, Oregon, USA
10
Department of Radiology, St Paul’s Hospital, Vancouver, British Columbia, Canada
11
Department of Medicine/Physiology, Queens University, Kingston, Ontario, Canada
12
Ottawa Hospital Research Institute, University of Ottawa, Ottawa, Ontario, Canada
Acknowledgements The authors thank the men and women who participated in
the study and individuals in the CanCOLD Collaborative research Group: Executive
Committee: Jean Bourbeau, (Mcgill University, Montreal, QC, Canada); Wan C Tan,
J Mark FitzGerald; D D Sin. (UBC, Vancouver, BC, Canada); D D Marciniuk (University
of Saskatoon, Saskatoon, SASK, Canada) D E O’Donnell (Queen’s University,
Kingston, ON, Canada); Paul Hernandez (University of Halifax, Halifax, NS, Canada);
Kenneth R Chapman (University of Toronto, Toronto, ON, Canada); Robert Cowie
(University of Calgary, Calgary, AB, Canada); Shawn Aaron (University of Ottawa,
Ottawa, ON, Canada); F Maltais (University of Laval, Quebec City, QC, Canada);
International Advisory Board: Jonathon Samet (the Keck School of Medicine of USC,
California, USA); Milo Puhan ( John Hopkins School of Public Health, Baltimore, USA
); Qutayba Hamid (McGill University, Montreal, Qc, Canada); James C Hogg (UBC
James Hogg Research Center, Vancouver, BC, Canada). Operations Center: Jean
Bourbeau (PI), Carole Baglole, Carole Jabet, Palmina Mancino, Yvan Fortier,
(University of McGill, Montreal, QC, Canada); Wan C Tan (co-PI), Don Sin, Sheena
Tam, Jeremy Road, Joe Comeau, Adrian Png, Harvey Coxson, Miranda Kirby, Jonathon
Leipsic, Cameron Hague (University of British Columbia James Hogg Research Center,
Vancouver, BC, Canada). Economic Core: Mohsen Sadatsafavi (University of British
Columbia, Vancouver, BC). Public Health core: Teresa To, Andrea Gershon (University
of Toronto) Data management and Quality Control: Wan C Tan, Harvey Coxson, (UBC,
Vancouver, BC, Canada); Jean Bourbeau, Pei-Zhi Li, Jean-Francois Duquette, Yvan
Fortier, Andrea Benedetti, Denis Jensen (Mcgill University, Montreal, QC,Canada),
Denis O’Donnell (Queen’s University, Kingston, ON, Canada. Field Centers: Wan C
Tan (PI), Christine Lo, Sarah Cheng, Cindy Fung, Nancy Ferguson, Nancy Haynes,
Junior Chuang, Licong Li, Selva Bayat, Amanda Wong, Zoe Alavi, Catherine Peng, Bin
Zhao, Nathalie Scott-Hsiung, Tasha Nadirshaw (UBC James Hogg Research Center,
Vancouver, BC); Jean Bourbeau (PI), Palmina Mancino, David Latreille, Jacinthe Baril,
Laura Labonte (McGill University, Montreal, QC, Canada ); Kenneth Chapman (PI),
Patricia McClean, Nadeen Audisho, (University of Toronto, Toronto, ON, Canada);
Robert Cowie (PI), Ann Cowie, Curtis Dumonceaux, Lisette Machado(University of
Calgary,Calgary, AB, Canada); Paul Hernandez (PI), Scott Fulton, Kristen Osterling
(University of Halifax, Halifax, NS, Canada ); Shawn Aaron (PI), Kathy Vandemheen,
Gay Pratt, Amanda Bergeron (University of Ottawa, Ottawa, ON, Canada); Denis
O’Donnell (PI), Matthew McNeil, Kate Whelan (Queen’s University, Kingston, ON,
Canada); Francois Maltais (PI), Cynthia Brouillard (University of Laval, Quebec City,
QC, Canada); Darcy Marciniuk (PI), Ron Clemens, Janet Baran (University of
Saskatoon, Saskatoon, SK, Canada).
Collaborators CanCOLD Collaborative Research Group (listed in
acknowledgements).
Contributors WCT contributed to the conception and design of the study, the
acquisition of the data, the analysis of the data and the writing. She assembled the
data set and takes responsibility for the integrity of the data and the accuracy of the
data analysis. JB, JMF, RC, KRC, PH, SDA, DDM, DEO, FM, CH, JL and JR contributed
to the acquisition of the data and the writing and revision of the article. ASB and JCH
contributed to the conception, design of the study and the revision of the article. DDS,
MK, HC contributed to the analysis and interpretation of the data and the writing of
the article. All authors approved the final version of the manuscript.
Funding The Canadian Cohort of Obstructive Lung Disease (COLD/CanCOLD) is
funded by the Canadian Institute of Heath Research (CIHR/Rx&D Collaborative
Research Program Operating Grants- 93326); the Respiratory Health Network of the
FRSQ; the Canadian Respiratory Research Network (CRRN); the Canadian Institutes
of Health Research (CIHR)—Institute of Circulatory and Respiratory Health; Canadian
Lung Association (CLA)/Canadian Thoracic Society (CTS); British Columbia Lung
Association; industry partners Astra Zeneca Canada, Boehringer-Ingelheim Canada,
GlaxoSmithKline Canada, Merck, Novartis Pharma Canada, Nycomed Canada, Pfizer
Canada; The funders had no role in the study design, data collection and analysis,
decision to publish or preparation of the manuscript.
Competing interests WCT and JB report unrestricted educational grants from
GSK, Pfizer, BI, AZ for the epidemiological COLD study; grants from funding for the
operations of CanCOLD Longitudinal Epidemiological Study from the Canadian
Institute of Heath Research (CIHR/Rx&D Collaborative Research Program Operating
Grants93326) with industry partners AZ Canada, BI Canada, GSK Canada, Merck,
Novartis Pharma Canada, Nycomed Canada, Pfizer Canada, outside the submitted
work. WCT also received personal fees from GSK board membership. DDM, an
employee of the University of Saskatchewan, received funding from the Canadian
Institutes of Health Research (via McGill University) to undertake this research. KRC
reports grants from Novartis, grants from Almirall, grants from Boehringer Ingelheim,
grants from Forest, grants from GSK, grants from AstraZeneca, grants from Amgen,
grants from Roche, grants from CSL Behring, grants from Grifols, grants from
Genentech, grants from Kamada, during the conduct of the study; others from
CIHRGSK Research Chair in Respiratory Health Care Delivery, outside the submitted
work. P H reports grants from Canadian Institute Health Research, during the
conduct of the study; grants and personal fees from AstraZeneca, Boehringer
Ingelheim, GlaxoSmithKline, Merck, Novartis, Takeda, Grifols, CSL Behring, Pfizer,
Almirall outside the submitted work. FM received fees for speaking at conferences
sponsored by Boehringer Ingelheim, GlaxoSmithKline and Novartis and Grifols. He
received research grants for participating in multicentre trials sponsored by
GlaxoSmithKline, Boehringer Ingelheim, Astra Zeneca, Nycomed and Novartis. He
received unrestricted research grant from Boehringer Ingelheim and GlaxoSmithKline.
He holds a CIHR/GSK research chair on COPD. DDS reports personal fees from
Almirall, personal fees from AstraZeneca, grants from AstraZeneca, personal fees
from Novartis, personal fees from Amgen, outside the submitted work; SDA, ASB,
JCH, JMF, CH, JL, JR, MK, HC, DEO and RC have no conflicts of interest to declare.
Ethics approval The study was approved by the respective university and
institutional ethical review boards :UBC/ PHC Research Ethics Board, P05-006
(Vancouver); Biomedical-C Research Ethics Board, BMC-06-002 (Montreal); UHN
REB, 06-0421-B (Toronto); Capital Health Research Ethics Board, CDHA-RS/
2007-255 (Halifax); Conjoint Health Research Ethics Board, ID21258 (Calgary);
DMED-1240-09 (Kingston); 2009519-01H (Ottawa); Bio-REB09-162 (Saskatoon);
CER20459 (Quebec City).
Provenance and peer review Not commissioned; externally peer reviewed.
Data sharing statement Data sharing is available via the CANCOLD process
through WCT (e mail: wan.tan@hli.ubc.ca) and JB (e mail: jean.bourbeau@mcgill.ca).
Tan WC, et al.Thorax 2015;0:1–8. doi:10.1136/thoraxjnl-2015-206938 7
Chronic obstructive pulmonary disease
group.bmj.com on June 6, 2015 - Published by http://thorax.bmj.com/Downloaded from

REFERENCES
1 Smith M, Li L, Augustyn M, et al. Prevalence and correlates of airflow obstruction in
approximately 317,000 never-smokers in China. Eur Respir J 2014;44:66–77.
2 Salvi SS, Barnes PJ. Chronic obstructive pulmonary disease in non-smokers. Lancet
2009;374:733–43.
3 Shahab L, Jarvis MJ, Britton J, et al. Prevalence, diagnosis and relation to tobacco
dependence of chronic obstructive pulmonary disease in a nationally representative
population sample. Thorax 2006;61:1043–7.
4 Lundback B, Lindberg A, Lindstrom M, et al. Not 15 but 50% of smokers develop
COPD?—Report from the Obstructive Lung Disease in Northern Sweden Studies.
Respir Med 2003;97:115–22.
5 Celli BR, Halbert RJ, Nordyke RJ, et al. Airway obstruction in never smokers: results
from the Third National Health and Nutrition Examination Survey. Am J Med
2005;118:1364–72.
6 Zhou Y, Wang C, Yao W, et al. COPD in Chinese nonsmokers. Eur Respir J
2009;33:509–18.
7 Bridevaux PO, Probst-Hensch NM, Schindler C, et al. Prevalence of airflow
obstruction in smokers and never-smokers in Switzerland. Eur Respir J
2010;36:1259–69.
8 Lamprecht B, McBurnie MA, Vollmer WM, et al. COPD in never smokers: results
from the population-based burden of obstructive lung disease study. Chest
2011;139:752–63.
9 Perez-Padilla R, Fernandez R, Lopez Varela MV, et al. Airflow obstruction in never
smokers in five Latin American cities: the PLATINO study. Arch Med Res
2012;43:159–65.
10 Eisner MD, Anthonisen N, Coultas D, et al.Anofficial American Thoracic Society
public policy statement: Novel risk factors and the global burden of chronic
obstructive pulmonary disease. Am J Respir Crit Care Med 2011;182:693–718.
11 Aryal S, Diaz-Guzman E, Mannino DM. COPD and gender differences: an update.
Transl Res 2013;162:208–18.
12 Perez-Padilla R, Schilmann A, Riojas-Rodriguez H. Respiratory health effects of
indoor air pollution. Int J Tuberc Lung Dis 2010;14:1079–86.
13 Behrendt CE. Mild and moderate-to-severe COPD in nonsmokers: distinct
demographic profiles. Chest 2005;128:1239–44.
14 Chilvers ER, Lomas DA. Diagnosing COPD in non-smokers: splitting not lumping.
Thorax 2010;65:465–6.
15 Buist AS, McBurnie MA, Vollmer WM, et al. International variation in the
prevalence of COPD (the BOLD Study): a population-based prevalence study. Lancet
2007;370:741–50.
16 Tan WC, Bourbeau J, FitzGerald JM, et al. Can age and sex explain the variation in
COPD rates across large urban cities? A population study in Canada. Int J Tuberc
Lung Dis 2011;15:1691–8.
17 GOLD. Global strategy for Diagnosis, Management, and Prevention of COPD, Global
Initiative for Chronic Obstructive Lung Disease (GOLD). 2015. http://www.goldcopd.
org/ (accessed 2 Feb 2015).
18 Hankinson JL, Odencrantz JR, Fedan KB. Spirometric reference values from a sample
of the general U.S. population. Am J Respir Crit Care Med 1999;159:179–87.
19 Bourbeau J, Tan WC, Benedetti A, et al. Canadian Cohort Obstructive Lung Disease
(CanCOLD): Fulfilling the need for longitudinal observational studies in COPD.
COPD 2012;11:125–32.
20 Barr RG, Berkowitz EA, Bigazzi F, et al. A combined pulmonary-radiology workshop
for visual evaluation of COPD: study design, chest CT findings and concordance
with quantitative evaluation. COPD 2012;9:151–9.
21 Miller MR, Hankinson J, Brusasco V, et al. Standardisation of spirometry. Eur Respir
J2005;26:319–38.
22 Birring SS, Brightling CE, Bradding P, et al. Clinical, radiologic, and induced sputum
features of chronic obstructive pulmonary disease in nonsmokers: a descriptive
study. Am J Respir Crit Care Med 2002;166:1078–83.
23 Ramirez-Venegas A, Sansores RH, Quintana-Carrillo RH, et al. FEV1 decline in
patients with chronic obstructive pulmonary disease associated with biomass
exposure. Am J Respir Crit Care Med 2014;190:996–1002.
24 Lange P, Parner J, Vestbo J, et al. A 15-year follow-up study of ventilatory function
in adults with asthma. N Engl J Med 1998;339:1194–200.
25 Rehfuess E, Mehta S, Pruss-Ustun A. Assessing household solid fuel use: multiple
implications for the Millennium Development Goals. Environ Health Perspect
2006;114:373–8.
26 Sorheim IC, Johannessen A, Gulsvik A, et al. Gender differences in COPD: are
women more susceptible to smoking effects than men? Thorax 2010;65:480–5.
27 Dijkstra A, Vonk JM, Jongepier H, et al. Lung function decline in asthma:
association with inhaled corticosteroids, smoking and sex. Thorax 2006;61:105–10.
28 Svanes C, Sunyer J, Plana E, et al. Early life origins of chronic obstructive pulmonary
disease. Thorax 2010;65:14–20.
29 Thomsen M, Nordestgaard BG, Vestbo J, et al. Characteristics and outcomes of
chronic obstructive pulmonary disease in never smokers in Denmark: a prospective
population study. Lancet Respir Med 2013;1:543–50.
30 Wedzicha JA, Brill SE, Allinson JP, et al. Mechanisms and impact of the frequent
exacerbator phenotype in chronic obstructive pulmonary disease. BMC Med
2013;11:181.
31 Han MK, Agusti A, Calverley PM, et al. Chronic obstructive pulmonary disease
phenotypes: the future of COPD. Am J Respir Crit Care Med 2010;182:598–604.
32 Tan WC, Bourbeau J, Hernandez P, et al. Exacerbation-like respiratory symptoms in
individuals without chronic obstructive pulmonary disease: results from a
population-based study. Thorax 2014;69:709–17.
33 Vestbo J. COPD: definition and phenotypes. Clin Chest Med 2014;35:1–6.
34 Mannino DM, Sonia Buist A, Vollmer WM. Chronic obstructive pulmonary
disease in the older adult: what defines abnormal lung function? Thorax
2007;62:237–41.
35 Guder G, Brenner S, Angermann CE, et al. GOLD or lower limit of normal
definition? A comparison with expert-based diagnosis of chronic obstructive
pulmonary disease in a prospective cohort-study. Respir Res 2012;13:13.
8 Tan WC, et al.Thorax 2015;0:1–8. doi:10.1136/thoraxjnl-2015-206938
Chronic obstructive pulmonary disease
group.bmj.com on June 6, 2015 - Published by http://thorax.bmj.com/Downloaded from

results from the CanCOLD study
and ever-smokers in the general population:
Characteristics of COPD in never-smokers
CanCOLD Collaborative Research Group
Kirby, H Coxson, C Hague, J Leipsic, D E O'Donnell, S D Aaron and
M FitzGerald, D D Marciniuk, F Maltais, A S Buist, J Road, J C Hogg, M
W C Tan, D D Sin, J Bourbeau, P Hernandez, K R Chapman, R Cowie, J
published online June 5, 2015Thorax
8
http://thorax.bmj.com/content/early/2015/06/05/thoraxjnl-2015-20693
Updated information and services can be found at:
These include:
Material
Supplementary
8.DC1.html
http://thorax.bmj.com/content/suppl/2015/06/05/thoraxjnl-2015-20693
Supplementary material can be found at:
References
#BIBL8
http://thorax.bmj.com/content/early/2015/06/05/thoraxjnl-2015-20693
This article cites 34 articles, 11 of which you can access for free at:
service
Email alerting box at the top right corner of the online article.
Receive free email alerts when new articles cite this article. Sign up in the
Collections
Topic Articles on similar topics can be found in the following collections
(177)Tobacco use (youth)
(771)Child health (925)Tobacco use (1140)TB and other respiratory infections
(924)Smoking (681)Radiology (diagnostics)
(738)Lung function (1085)Health education
(1643)Asthma (1023)Airway biology
Notes
http://group.bmj.com/group/rights-licensing/permissions
To request permissions go to:
http://journals.bmj.com/cgi/reprintform
To order reprints go to:
http://group.bmj.com/subscribe/
To subscribe to BMJ go to:
group.bmj.com on June 6, 2015 - Published by http://thorax.bmj.com/Downloaded from