Risk factors for chronic obstructive pulmonary disease among never-smokers in Korea

Figures & data

Figure 1 Flow diagram of the process of enrollment of 3,473 never-smoker subjects in the fourth Korean National Health and Nutrition Examination Survey (KNHANES).

Abbreviation: PFT, pulmonary function test.

Table 1 Baseline characteristics of the never-smoker subjects

Parameters	Total		COPD		Non-COPD		P-value
	N, crude	Weighted, % (SE)	N, crude	Weighted, % (SE)	N, crude	Weighted, % (SE)
Sex
Male	420	13.9 (0.7)	71	28.4 (3.7)	349	12.7 (0.7)	<0.0001
Female	3,053	86.1 (0.7)	187	71.6 (3.7)	2,866	87.3 (0.7)
Age in years (mean ± SE)				66±0.9		54±0.3
40–49	1,191	40.0 (1.2)	23	11.1 (2.6)	1,168	42.4 (1.2)	<0.0001
50–59	1,021	28.9 (1.1)	50	20.4 (3.4)	971	29.6 (1.1)
60–69	790	16.9 (0.7)	80	24.1 (3.1)	710	16.3 (0.7)
70–79	429	12.5 (0.8)	93	37.5 (4.1)	336	10.4 (0.8)
≥80	42	1.7 (0.3)	12	6.9 (2.3)	30	1.3 (0.3)
BMI in kg/m^2
<18.5	47	1.3 (0.2)	10	1.3 (0.2)	37	1.1 (0.2)	0.005
18.5–24.9	2,187	63.4 (1.1)	168	63.4 (1.1)	2,019	63.1 (1.2)
≥25.0	1,237	35.3 (1.2)	78	35.3 (1.2)	1,159	35.8 (1.2)
Secondhand smoke
No	2,437	68.7 (1.1)	196	76.8 (3.5)	2,241	68.0 (1.1)	0.026
Yes	1,036	31.3 (1.1)	62	23.2 (3.5)	974	32.0 (1.1)
Education level
Elementary school or less	1,449	37.4 (1.2)	162	60.1 (4.1)	1,287	35.5 (1.2)	<0.0001
Middle school	549	16.0 (0.8)	40	17.8 (3.0)	509	15.8 (0.8)
High school	953	29.8 (1.1)	30	10.7 (2.5)	923	31.3 (1.1)
College or more	518	16.9 (1.1)	25	5.1 (1.4)	493	17.3 (1.1)
Occupation
Managers/professional	232	7.5 (0.6)	10	3.1 (1.3)	222	7.8 (0.6)	<0.0001
Office worker	121	3.6 (0.4)	6	2.5 (1.2)	115	3.7 (0.4)
Service/sales worker	522	16.9 (0.9)	14	5.2 (1.9)	508	17.9 (1.0)
Agriculture/fishery worker	423	7.7 (0.9)	50	14.4 (2.9)	373	7.2 (0.8)
Skilled labor/machine operator	164	5.5 (0.5)	12	5.8 (2.3)	152	5.4 (0.7)
Manual laborer (construction, mining)	412	11.8 (0.7)	39	15.5 (3.1)	376	11.4 (0.7)
No labor	1,576	47.0 (1.2)	124	53.5 (4.1)	1,452	46.5 (1.3)
Living with partner
Yes	2,729	80.0 (0.9)	184	68.1 (3.9)	2,545	81.0 (0.9)	<0.0001
No	735	20.0 (0.9)	73	31.9 (3.9)	662	19.0 (0.9)
Family income
High	1,755	54.1 (1.4)	85	37.3 (4.3)	1,670	55.4 (1.4)	<0.0001
Low	1,647	45.9 (1.4)	159	62.7 (4.3)	1,488	44.6 (1.4)
Medical condition
Diabetes mellitus	277	7.7 (0.6)	29	11.9 (2.6)	248	7.3 (0.6)	0.041
Hypertension	888	24.6 (1.0)	103	38.0 (4.0)	785	23.5 (1.0)	<0.0001
Cancer	139	4.1 (0.4)	12	4.1 (1.4)	127	4.1 (0.4)	0.948
Lung cancer	2	0	2	0.4 (0.3)	0	0	<0.0001
History of pulmonary TB	180	5.4 (0.5)	32	16.8 (3.4)	139	4.3 (0.4)	<0.0001
Bronchiectasis	19	0.6 (0.2)	8	2.7 (1.2)	11	0.4 (0.1)	<0.0001
Chronic liver disease	82	2.3 (0.3)	1	0.2 (0.2)	81	2.4 (0.3)	0.003
Anemia (Hb <12.0 g/dL)	443	13.4 (0.8)	26	8.0 (1.9)	417	13.3 (0.8)	0.725

Abbreviations: SE, standard error; COPD, chronic obstructive pulmonary disease; BMI, body mass index; TB, tuberculosis; Hb, hemoglobin.

Table 2 Risk factors for COPD in the never-smoker subjects

Factor	Univariate analysis			Multivariate analysis
	Odds ratio	95% confidence interval	P-value	Odds ratio	95% confidence interval	P-value
Sex
Male	2.7	1.9–4.0	<0.0001	4.2	2.6–6.7	<0.0001
Female	Reference			Reference
Age in years
40–49	Reference			Reference
50–59	2.6	1.4–5.0	0.003	1.7	0.9–3.3	0.135
60–69	5.68	3.3–9.8	<0.0001	3.8	2.0–7.0	<0.0001
70–79	13.8	7.6–25.2	<0.0001	9.2	4.6–18.7	<0.0001
≥80	20.5	8.1–51.6	<0.0001	17.7	6.3–49.4	<0.0001
BMI (kg/m^2)
<18.5	3.1	1.3–7.1	<0.0001	3.1	1.0–9.4	0.045
18.5–24.9	Reference			Reference
≥25.0	0.8	0.5–1.1	0.11	0.7	0.5–0.9	0.046
Secondhand smoke
No	Reference			Reference
Yes	0.6	0.4–0.9	0.027	1.1	0.7–1.7	0.711
Education level
High school or more	Reference			Reference
Middle school or less	3.4	2.2–5.1	<0.0001	2.0	1.2–3.2	0.007
Occupation
Manager/professional/office worker/service/sales worker	Reference			Reference
Agriculture/fishery worker	5.4	2.9–10.2	<0.0001	1.9	0.9–4.1	0.563
Skilled labor/machine operator	2.9	1.1–7.5	0.027	1.3	0.5–3.5	0.100
Manual laborer (construction, mining)	3.7	1.9–7.2	<0.0001	2.6	1.3–5.3	0.007
No labor	3.1	1.8–5.3	<0.0001	1.5	0.8–3.1	0.226
Living with partner
Yes	Reference			Reference
No	2.0	1.4–2.9	<0.0001	1.2	0.8–1.8	0.301
Family income
High	Reference			Reference
Low	2.1	1.4–3.0	<0.0001	0.9	0.6–1.4	0.710
Diabetes mellitus
No	Reference			Reference
Yes	1.7	1.0–3.0	0.043	1.1	0.6–1.9	0.888
Hypertension
No	Reference			Reference
Yes	2.0	1.4–2.8	<0.0001	0.9	0.6–1.3	0.467
Anemia
No	Reference			–	–	–
Yes	1.1	0.6–1.9	0.725
History of pulmonary tuberculosis
No	Reference			Reference
Yes	4.5	2.7–7.5	<0.0001	4.5	2.3–8.7	<0.0001
Bronchiectasis
No	Reference			Reference
Yes	7.0	2.2–22.2	0.007	6.0	1.4–25.4	0.016
Cancer
No	Reference			–	–	–
Yes	1.0	0.5–2.09	0.948

Abbreviations: BMI, body mass index; COPD, chronic obstructive pulmonary disease.

Table S1 Demography and severity of never-smoker COPD and smoker COPD

Factors	Never-smoker COPD N (%)	Smoker COPD N (%)	P-value
Subjectsa	258	562	–
Sex, female	187 (71.6)	40 (7.5)	<0.0001
Age, mean ± SE	65.7±0.9	62.8±0.6	0.008
COPD severity			0.205
Mild	108 (44.8)	247 (43.3)
Moderate	142 (53.5)	282 (52.0)
Severe	6 (1.6)	29 (4.4)
Very severe	0	3 (0.3)

Notes:

a Patients with COPD were recruited from 5,784 subjects designated in Figure 1.

Abbreviations: COPD, chronic obstructive pulmonary disease; SE, standard error.

Table S2 Multivariate analysis of risk factors for COPD in total subjects and ever-smokers

Factors	Total			Ever-smoker
	OR	95% CI	P-value	OR	95% CI	P-value
Sex
Male	5.9	4.5–7.8	<0.0001	2.6	1.5–4.5	0.001
Female	Reference			Reference
Age (years)
40–49	Reference			Reference
50–59	2.4	1.7–3.5	<0.0001	2.8	1.8–4.4	<0.0001
60–69	5.9	4.0–8.7	<0.0001	7.2	4.6–11.5	<0.0001
70–79	13.4	8.8–20.5	<0.0001	15.6	9.0–27.0	<0.0001
≥80	16.2	7.3–36.3	<0.0001	8.4	2.9–24.7	<0.0001
BMI (kg/m^2)
<18.5	2.1	1.1–4.1	0.022	1.6	0.72–3.3	0.245
18.5–24.9	Reference			Reference
≥25.0	0.7	0.5–0.9	0.006	0.7	0.5–1.0	0.049
Secondhand smoking
No	Reference			Reference
Yes	1.2	0.9–1.5	0.266	1.1	0.8–1.6	0.458
Education level
High school or more	Reference			Reference
Middle school or less	1.7	1.3–2.2	<0.0001	1.6	1.2–2.2	0.005
Occupation
Manager/professional/office worker/service/sales worker	Reference			Reference
Agriculture/fishery worker	1.4	0.9–2.1	0.156	1.2	0.7–1.9	0.535
Skilled labor/machine operator	1.0	0.7–1.6	0.909	0.9	0.6–1.5	0.769
Manual laborer (construction, mining)	2.2	1.5–3.1	<0.0001	1.2	1.2–3.4	0.006
No labor	1.5	1.0–2.1	0.044	1.4	0.9–2.2	0.146
Living with partner
Yes	Reference			Reference
No	1.3	1.0–1.7	0.077	1.2	0.8–1.4	0.441
Family income
High	Reference			Reference
Low	1.0	0.8–1.3	0.929	1.0	0.81–1.54	0.764
Diabetes mellitus
No	Reference			Reference
Yes	1.2	0.8–1.6	0.382	1.2	0.8–1.7	0.297
Hypertension
No	Reference			Reference
Yes	0.7	0.6–0.9	0.003	0.6	0.5–0.8	0.002
Pulmonary tuberculosis
No	Reference			Reference
Yes	2.9	1.9–4.3	<0.0001	2.3	1.5–3.6	<0.0001
Bronchiectasis
No	Reference			Reference
Yes	2.7	1.0–7.6	0.06	1.0	0.4–2.7	0.966

Abbreviations: COPD, chronic obstructive pulmonary disease; OR, odds ratio; CI, confidence interval; BMI, body mass index.