COPD and its association with smoking in the Mainland China: a cross-sectional analysis of 0.5 million men and women from ten diverse areas

Figures & data

Figure 1 Locations of the ten China Kadoorie Biobank survey sites across Mainland China.

Table 1 Baseline characteristics of the study participants by smoking category

Variable*	Men (n=210,057)			Women (n=302,438)
	Never	Occasional	All regular	Never	Occasional	All regular
All (N)	30,282	23,610	156,165	287,117	5,522	9,799
Study area
Urban	55.5	44.4	40.9	44.8	38.6	39.4
Rural	44.5	55.6	59.1	55.2	61.4	60.6
Age at baseline (years)	54.4±11.9	51.1±11.1	52.8±10.6	51.1±10.4	53.1±10.9	60.1±9.9
30–39	15.2	19.9	13.0	16.4	13.3	3.6
40–49	23.2	29.7	28.9	31.5	28.3	13.4
50–59	25.8	26.9	31.7	31.2	29.3	27.3
60–69	23.8	16.8	19.3	15.8	21.3	38.5
70–79	12.1	6.7	7.1	5.1	7.8	17.2
Annual household income (yuan; in thousands)
<5	8.4	8.6	9.5	9.4	20.2	25.6
5–9	14.9	16.6	17.2	19.4	23.4	25.0
10–19	28.4	28.9	28.2	29.6	29.6	28.8
20–34	26.7	24.6	25.3	24.7	16.8	13.4
≥35	21.6	21.2	19.8	16.9	10.1	7.3
Highest education completed
No formal school	7.3	5.8	9.6	25.0	21.2	34.9
Primary school	26.6	28.0	35.5	31.0	35.3	41.1
Middle/high school	50.0	54.4	49.2	39.4	38.6	22.6
College/university	16.1	11.8	5.7	4.5	4.9	1.4
Standing height (m)	1.65±0.07	1.65±0.06	1.65±0.06	1.54±0.06	1.53±0.07	1.52±0.06
FEV1 (L)	2.61±0.68	2.77±0.66	2.65±0.70	2.00±0.48	1.92±0.57	1.64±0.54
FVC (L)	3.06±0.75	3.27±0.74	3.16±0.77	2.36±0.54	2.31±0.60	2.03±0.57
FEV1/FVC (%)	85.5±8.9	84.6±8.1	83.6±9.3	85.0±7.8	82.7±9.1	80.2±10.2

Note:

* Data are % or mean ± SD.

Abbreviations: n, number; N, total number; FEV₁, forced expiratory volume in 1 second; FVC, forced vital capacity; SD, standard deviation.

Table 2 Associations of smoking with prevalent AFO and self-reported chronic bronchitis/emphysema among men

	Smoking habit (%)	AFO		Bronchitis/emphysema
		%‡	OR (95% CI)†	%‡	OR (95% CI)†
Smoking category
Never	14.4	5.4	1.00 (0.95–1.06)	3.3	1.00 (0.94–1.07)
Occasional	11.2	5.2	0.93 (0.88–1.00)	3.1	0.98 (0.90–1.06)
Exregular	13.3	7.4	1.50 (1.44–1.57)	5.6	1.85 (1.77–1.95)
Current regular	61.1	7.1	1.37 (1.34–1.41)	2.5	0.77 (0.74–0.80)
P heterogeneity			<0.0001		<0.0001
All regular	74.4	7.2	1.42 (1.34–1.50)	3.1	1.04 (0.96–1.11)
Amount smoked (g tobacco/day) in regular smokers
Mean (SD), 18.3 (10.8)
<5	6.1	6.6	1.34 (1.24–1.44)	3.3	0.99 (0.87–1.11)
5–14	28.9	6.9	1.36 (1.31–1.41)	2.9	0.95 (0.90–1.01)
15–24	46.2	7.4	1.46 (1.42–1.51)	3.2	1.03 (0.99–1.08)
25–34	10.4	7.6	1.47 (1.39–1.56)	3.4	1.11 (1.02–1.21)
≥35	8.4	7.4	1.42 (1.32–1.52)	4.3	1.32 (1.21–1.45)
P trend			0.014		<0.0001
Age started to smoke regularly (years) in regular smokers
Mean (SD), 22.5 (7.0)
≥28	6.3	5.9	1.15 (1.10–1.21)	4.2	0.76 (0.70–0.81)
24–27	27.7	6.5	1.27 (1.21–1.34)	3.7	0.92 (0.85–0.99)
20–23	32.9	7.4	1.48 (1.43–1.54)	3.4	1.12 (1.07–1.18)
16–19	16.1	8.1	1.60 (1.54–1.67)	2.8	1.24 (1.17–1.31)
<16	16.9	9.6	1.79 (1.68–1.92)	2.4	1.35 (1.22–1.49)
P trend			<0.0001		<0.0001
Depth of inhalation in regular smokers
Mouth/throat	51.8	7.0	1.35 (1.31–1.39)	2.9	0.94 (0.90–0.98)
Lung now	12.3	6.4	1.27 (1.19–1.35)	3.2	1.06 (0.97–1.15)
Lung always	35.9	7.7	1.58 (1.52–1.64)	3.6	1.19 (1.13–1.25)
P trend			<0.0001		<0.0001
Recent changes in amount smoked in current regular smokers§
No change	66.5	6.8	1.28 (1.24–1.32)	2.1	0.62 (0.59–0.65)
Increased a lot	15.3	6.9	1.33 (1.25–1.42)	2.4	0.72 (0.64–0.80)
Decreased a lot	12.7	9.0	1.77 (1.68–1.87)	4.3	1.20 (1.10–1.30)
P heterogeneity			<0.0001		<0.0001
Reason for stopping smoking in exregular smokers
Ill health	49.6	8.8	1.86 (1.77–1.96)	8.4	2.79 (2.64–2.95)
Other reason	50.4	5.6	1.08 (1.01–1.16)	2.7	0.90 (0.81–0.99)
P heterogeneity			<0.0001		<0.0001

Notes:

† Adjusted for region, 5-year age group, age group × region interaction, education, and income, with the never-smoker category as the reference group. With the exception of the comparison of all regular versus never-smokers, the CIs are floated, so that comparisons can be made between any pair of categories.

‡ Prevalences of disease are directly standardized to the age and area structure of the study’s male population.

§ The variable was missing in 5.4% of male current smokers (N=6,963 men).

Abbreviations: AFO, airflow obstruction; OR, odds ratio; CI, confidence interval; SD, standard deviation; N, total number.

Table 3 Associations of smoking with prevalent AFO and self-reported chronic bronchitis/emphysema among women

	Smoking habit (%)	AFO		Bronchitis/emphysema
		%‡	OR (95% CI)†	%‡	OR (95% CI)†
Smoking category
Never	94.9	4.3	1.00 (0.96–1.04)	2.2	1.00 (0.95–1.05)
Occasional	1.8	4.4	1.11 (1.00–1.22)	1.9	0.99 (0.84–1.15)
Exregular	0.9	5.0	1.67 (1.50–1.86)	4.0	2.31 (2.02–2.63)
Current regular	2.4	6.5	1.46 (1.36–1.57)	2.0	0.87 (0.77–0.99)
P heterogeneity			<0.0001		<0.0001
All regular	3.3	6.4	1.53 (1.43–1.65)	2.4	1.28 (1.15–1.42)
Amount smoked (g tobacco/day) in regular smokers
Mean (SD), 9.6 (7.5)
<5	27.4	6.3	1.38 (1.23–1.55)	2.2	1.14 (0.96–1.36)
5–14	48.9	5.6	1.64 (1.51–1.79)	2.6	1.32 (1.16–1.50)
15–24	20.5	7.1	1.48 (1.30–1.69)	2.3	1.37 (1.13–1.67)
25–34	2.0	9.2	1.58 (1.07–2.34)	2.3	1.49 (0.84–2.63)
≥35	1.2	9.8	1.79 (1.03–3.10)	5.9	1.10 (0.44–2.70)
P trend			0.269		0.1966
Age started to smoke regularly (years) in regular smokers
Mean (SD), 27.1 (11.9)
≥28	11.3	5.5	1.36 (1.23–1.52)	1.4	1.00 (0.85–1.18)
24–27	18.5	6.7	1.57 (1.33–1.86)	2.5	1.27 (0.98–1.66)
20–23	16.8	7.6	1.69 (1.47–1.93)	3.8	1.56 (1.28–1.90)
16–19	12.2	7.9	1.50 (1.32–1.70)	3.1	1.52 (1.26–1.84)
<16	41.1	9.4	1.82 (1.56–2.11)	1.9	1.45 (1.15–1.84)
P trend			0.0063		0.0005
Depth of inhalation in regular smokers
Mouth/throat	62.0	6.4	1.49 (1.39–1.61)	2.2	1.14 (1.02–1.29)
Lung now	12.6	7.0	1.68 (1.41–1.99)	2.2	1.28 (0.99–1.66)
Lung always	25.3	6.9	1.58 (1.39–1.78)	3.4	1.65 (1.40–1.95)
P trend			0.3214		0.0004
Recent changes in amount smoked in current regular smokers§
No change	62.5	6.3	1.37 (1.25–1.51)	1.8	0.69 (0.58–0.83)
Increased a lot	16.7	8.2	1.55 (1.30–1.86)	3.4	1.04 (0.77–1.41)
Decreased a lot	14.1	11.0	1.90 (1.61–2.24)	2.9	1.26 (0.96–1.65)
P heterogeneity			0.0056		0.0003
Reason for stopping smoking in ex regular smokers
Ill health	54.6	6.5	2.03 (1.78–2.31)	9.3	3.24 (2.78–3.78)
Other reason	45.4	5.2	1.20 (0.99–1.45)	2.0	1.22 (0.95–1.58)
P heterogeneity			<0.0001		<0.0001

Notes:

† Adjusted for region, 5-year age group, age group × region interaction, education, and income, with the never-smoker category as the reference group. With the exception of the comparison of all regular versus never-smokers, CIs are floated, so that comparisons can be made between any pair of categories.

‡ Prevalences of disease are directly standardized to the age and area structure of the study female population.

§ The variable was missing in 6.8% of female current smokers (N=485 women).

Abbreviations: AFO, airflow obstruction; OR, odds ratio; CI, confidence interval; SD, standard deviation; N, total number.

Figure 2 Prevalence of smoking and airflow obstruction in regular smokers in the ten areas.

Notes: (A and B) Prevalence of regular smoking in men and women, respectively. (C and D) Prevalence of airflow obstruction in men and women, respectively. The percentage of each shaded bar represents the percent of airflow obstruction cases in that region for smokers. Bars for all plots are order by the regional prevalence of regular smoking in men or women.
Abbreviations: R, rural; U, urban.

Table 4 ORs for prevalent AFO and self-reported chronic bronchitis/emphysema in regular versus never-smokers by sociodemographic factors

	Characteristics of regular smokers (crude mean or prevalence)					AFO			Bronchitis/emphysema
	Prevalence (%)	Age started (years)	Age at baseline (years)	Amount smoked (g tobacco/day)	Always inhaled to lungs (%)	Prevalence (%)‡		OR (95% CI)†	Prevalence (%)‡		OR (95% CI)†
						Never-smokers	Regular smokers		Never-smokers	Regular smokers
Men
Study area
Urban	70.1	22.6	52.9	18.0	42.7	3.1	5.2	1.72 (1.56–1.90)	3.2	3.1	1.13 (1.01–1.26)
Rural	77.6	22.4	52.8	18.6	31.1	7.0	8.7	1.28 (1.19–1.37)	3.3	3.2	0.96 (0.87–1.06)
P trend								<0.0001			0.0311
Age at baseline, years
<50	73.7	20.9	42.6	18.7	38.1	2.2	2.5	1.11 (0.96–1.27)	1.8	1.2	0.73 (0.62–0.87)
50–59	77.8	22.7	54.7	19.0	36.4	4.9	6.3	1.30 (1.15–1.46)	3.3	2.6	0.82 (0.71–0.95)
60–69	73.0	24.6	64.7	17.3	31.8	9.1	13.2	1.51 (1.37–1.66)	5.1	5.8	1.17 (1.03–1.32)
70–79	68.0	25.1	72.5	15.6	31.3	14.9	21.2	1.63 (1.45–1.83)	6.5	8.1	1.39 (1.18–1.62)
P trend								<0.0001			<0.0001
Annual household income (yuan, thousands)
<5	76.5	23.3	58.7	17.0	27.7	9.3	9.5	1.33 (1.17–1.52)	5.1	3.7	1.08 (0.88–1.32)
5–9	76.0	22.7	52.9	17.7	34.8	6.6	8.3	1.26 (1.11–1.44)	3.7	3.4	0.91 (0.76–1.08)
10–19	74.1	22.2	52.7	18.3	38.1	6.1	7.3	1.34 (1.20–1.49)	3.2	3.0	1.07 (0.93–1.24)
20–34	74.0	22.2	51.8	18.6	37.2	4.1	6.1	1.62 (1.41–1.85)	3.2	3.2	1.02 (0.87–1.18)
≥35	72.9	22.7	51.3	19.1	35.8	3.3	5.5	1.81 (1.53–2.14)	4.5	2.8	1.10 (0.93–1.30)
P trend								0.0005			0.5173
Women
Study area
Urban	2.9	29.5	61.0	9.7	29.1	3.4	5.5	2.04 (1.75–2.37)	2.4	2.6	1.51 (1.28–1.78)
Rural	3.5	25.6	59.6	9.5	22.9	5.0	7.1	1.44 (1.33–1.56)	2.0	2.3	1.17 (1.02–1.34)
P trend								<0.0001			0.0195
Age at baseline, years
<50	1.2	27.5	43.9	10.1	31.0	2.3	2.9	1.44 (1.14–1.81)	1.3	0.9	0.88 (0.57–1.36)
50–59	2.9	26.3	55.0	10.0	25.8	4.0	6.7	1.35 (1.18–1.54)	2.4	2.8	1.10 (0.88–1.37)
60–69	7.5	27.3	65.4	9.4	23.4	7.5	12.0	1.74 (1.56–1.94)	3.6	4.9	1.45 (1.25–1.69)
70–79	10.1	27.7	72.5	9.0	23.3	13.4	18.8	1.61 (1.38–1.87)	4.6	7.6	1.47 (1.17–1.84)
P trend								0.0497			0.0099
Annual household income (yuan, thousands)
<5	8.2	25.4	62.4	9.6	20.3	5.8	7.2	1.38 (1.22–1.55)	2.8	1.8	1.10 (0.90–1.33)
5–9	4.1	26.5	58.9	9.7	28.0	4.8	6.4	1.38 (1.21–1.59)	2.3	2.5	1.26 (1.02–1.57)
10–19	3.2	27.2	59.5	9.7	26.6	4.1	6.0	1.72 (1.49–1.98)	2.2	2.5	1.28 (1.04–1.57)
20–34	1.8	30.0	60.1	9.5	28.0	3.6	6.2	1.95 (1.57–2.43)	2.3	3.6	1.73 (1.32–2.27)
≥35	1.4	29.7	59.3	9.5	24.2	3.5	7.6	1.90 (1.40–2.59)	2.4	1.5	1.22 (0.82–1.84)
P trend								0.0005			0.0553

Notes:

† ORs are for all regular smokers versus never-smokers, adjusted for 5-year age group, region, age group × region interaction, education, and income.

‡ Prevalences of the disease are directly standardized to the age and area structure of the population in the China Kadoorie Biobank.

Abbreviations: OR, odds ratio; AFO, airflow obstruction; CI, confidence interval.