Current asthma contributes as much as smoking to chronic bronchitis in middle age: a prospective population-based study

Figures & data

Table 1 Main characteristics of all TAHS participants (and nonresponders) to the 2004 postal survey, stratified by adult chronic bronchitis

Clinical characteristics	Self-reported adult CB			Nonresponders (n=2,720)a
	(N=5,565 [%])		P-value
	No (n=5,224 [94])	Yes (n=341 [6])
Demographics
Age in years, mean (SD)	42.8 (0.9)	42.9 (0.9)	0.771	–
Sex (male)	2,673 (51)	193 (57)	0.052	1,379 (51)
Cigarette smoking
Nonsmokers	2,140 (42)	79 (24)	<0.001	–
Ex-smoker <20 pack-years	1,173 (23)	46 (14)	<0.001	–
Ex-smoker >20 pack-years	353 (7)	13 (4)	0.034	–
Current <20 pack-years	701 (14)	51 (15)	0.421	–
Current >20 pack-years	708 (14)	143 (43)	<0.001	–
Asthma and/or wheezy breathing
Asthma 1968	889 (17)	92 (27)	<0.001	405 (15)
Asthma 2004
None	3,051 (58)	72 (21)	<0.001	–
Remitted	1,154 (22)	42 (12)	<0.001	–
Current	1,017 (19)	227 (66)	<0.001	–
Allergic history
Any allergy 1968	1,732 (34)	139 (42)	0.002	856 (33)
Any allergy 2004	2,475 (47)	224 (66)	<0.001	–
Childhood bronchitis
At least two episodes	2,043 (40)	147 (45)	0.071	958 (36)
At least ten episodes	434 (8)	47 (14)	0.015	218 (8)

Notes: Those with missing data were excluded from individual totals.

a Consists of those not traced or those traced but not responding to the 2004 postal survey. Mean comparison test (age only) and cohort study summary statistics using Stata 12 SE was used to obtain the P-values.

Abbreviations: TAHS, Tasmanian Longitudinal Health Study; CB, chronic bronchitis; SD, standard deviation.

Table 2 Independent associations between clinical characteristics and CB in middle age

Clinical characteristics	Self-reported adult CB (N=4,949 [%])
	No (n=4,658 [94])	Yes (n=291 [6])	Univariable P for trend	Adjusted OR (95% CI)a
Male sex	2,377 (51)	168 (58)	–	1.46 (1.12, 1.90)*
Combined smoking history			<0.001
None	1,986 (43)	78 (27)		1
Ex-smoker <20 pack-years	1,094 (23)	43 (15)		0.99 (0.67, 1.46)
Ex-smoker >20 pack-years	331 (7)	12 (4)		0.86 (0.44, 1.59)
Current <20 pack-years	625 (13)	42 (14)		1.54 (1.03, 2.32)*
Current >20 pack-years	622 (13)	116 (40)		3.03 (2.14, 4.30)**
Smoking status			<0.001
Never	1,986 (43)	77 (26)		1
Past	1,425 (31)	56 (19)		0.62 (0.30, 1.30)
Current	1,246 (27)	158 (54)		1.36 (0.64, 2.88)
Pack-year history			<0.001
None	2,283 (49)	85 (29)		1
Up to 10 pack-years	828 (18)	42 (14)		1.47 (0.69, 3.11)
Between 10 and 20 pack-years	638 (14)	38 (13)		1.38 (0.64, 2.98)
Between 20 and 40 pack-years	747 (16)	85 (29)		1.90 (0.90, 4.00)
>40 pack-years	162 (3)	40 (14)		3.19 (1.42, 7.17)***
Asthma/wheezy breathing			<0.001
Never	2,723 (58)	65 (22)		1
Remitted	1,035 (22)	38 (13)		1.29 (0.85, 1.96)
Current (last 12 months)	900 (19)	188 (65)		6.19 (4.55, 8.42)**
Allergy history			–
Any history	2,218 (48)	195 (67)		2.07 (1.57, 2.73)**
Passive smoking			<0.001
None	3,490 (75)	166 (57)		1
Between 1 and 3 hours/day	735 (16)	58 (20)		1.05 (0.75, 1.47)
At least 4 hours/day	433 (9)	67 (23)		1.31 (0.92, 1.87)
Parental bronchitis at least every 3 years in 1968			–
Neither parent	4,071 (87)	232 (80)		1
Either or both	587 (13)	59 (20)		1.13 (0.82, 1.57)

Notes: Those with missing data were excluded from individual analyses.

a All exposure variables are adjusted for one another in addition to participant education and occupation (estimates included in Table S1). The combined smoking variable was initially used, then substituted for separate smoking status and pack-year variables;

* P<0.05;

** P<0.001;

*** P<0.01.

Abbreviations: CB, chronic bronchitis; CI, confidence interval; OR, odds ratio.

Table 3 Multivariable associations between allergy history and CB in middle age

Allergy history in 2004	Self-reported adult CB (N=4,949 [%])
	No (n=4,658 [94])	Yes (n=291 [6])	Adjusted OR (95% CI)a
Any history	2,218 (48)	195 (67)	2.07 (1.57, 2.73)*
Food allergy	542 (10)	62 (18)	1.80 (1.22, 2.63)**
Medicine allergy	825 (16)	67 (20)	1.19 (0.83, 1.70)
Dust allergy	787 (15)	104 (31)	Males: 2.04 (1.23, 3.38)*** Females: 2.62 (1.67, 4.12)* P [interaction] =0.017
Animal allergy	536 (10)	66 (19)	1.85 (1.26, 2.69)***
Pollen allergy	1,525 (29)	158 (46)	1.81 (1.35, 2.43)*
Ever eczema	1,859 (36)	173 (51)	1.67 (1.26, 2.22)*
Hay fever	2,547 (49)	233 (69)	1.76 (1.30, 2.40)*

Notes: Those with missing data were excluded from individual analyses.

a Adjusted for male sex, current wheezing 2004, smoking (status and pack-years), parental bronchitis 1968, highest attained educational level, and participant occupation 2004;

* P<0.001;

** P<0.05;

*** P<0.01.

Abbreviations: CB, chronic bronchitis; CI, confidence interval; OR, odds ratio.

Table 4 Independent associations between early-life factors and CB in middle age

Clinical characteristics when participants were aged 7 years	Self-reported adult CB (N=5,170 [%])
	No (n=4,862 [94])	Yes (n=308 [6])	Univariable P for trend	Adjusted OR (95% CI)a
Male sex	2,485 (51)	179 (58)	–	1.39 (1.09, 1.77)*
Childhood bronchitis
None	2,492 (52)	133 (45)	0.001	1
1 episode only	384 (8)	30 (10)		1.38 (0.91, 2.08)
2–5 episodes	990 (21)	54 (18)		0.85 (0.60, 1.19)
5–10 episodes	519 (11)	36 (12)		0.94 (0.62, 1.42)
11–20 episodes	235 (5)	23 (8)		1.20 (0.72, 2.00)
>20 episodes	165 (3)	20 (7)		1.33 (0.75, 2.35)
Chronic symptoms	31 (1)	3 (1)		1.36 (0.45, 4.07)
Asthma status
No asthma	4,046 (83)	227 (74)	<0.001	1
Remitted asthma	225 (5)	18 (6)		1.17 (0.71, 1.92)
Current asthma	495 (10)	59 (20)		1.84 (1.26, 2.68)*
Asthma severity
No asthma	4,046 (83)	227 (74)	<0.001	1
“Infrequent intermittent”	406 (8)	36 (12)		1.39 (0.92, 2.10)
\“Frequent intermittent”	25 (1)	2 (1)		0.49 (0.64, 3.78)
“Episodic”	139 (3)	22 (7)		2.32 (1.38, 3.92)*
“Moderate-to-severe persistent”	21 (0.4)	3 (1)		1.81 (0.51, 6.45)
Allergy history			–
Any allergy	1,627 (33)	133 (43)		1.35 (1.05, 1.73)**
Hives, at least once	963 (20)	84 (27)		1.34 (1.02, 1.76)**
Bronchial symptoms reported by parent			<0.001
Neither parent	3,841 (79)	206 (67)		1
One or either parent	871 (18)	79 (26)		1.61 (1.22, 2.13)*
Both parents	150 (3)	23 (7)		2.51 (1.56, 4.06)***

Notes: Those with missing data were excluded from individual analyses.

a All exposure variables are adjusted for one another in addition to paternal occupation (estimates included in Table S1). The “any allergy” variable was initially used, then hives only was substituted. Similarly, asthma status and asthma severity as well as bronchitis frequency and chronicity were substituted with other variables retained;

* P<0.01;

** P<0.05;

*** P<0.001.

Abbreviations: CB, chronic bronchitis; CI, confidence interval; OR, odds ratio.

Table 5 Relative associations between adult smoking, asthma, and allergy on airflow obstruction, CB, and its overlap

Clinical characteristics in middle age	The CB–COPD overlap (N=1,307, adjusted OR [95% CI]a)
	Spirometrically defined COPD only (n=95)	Nonobstructive CB (n=127)	Obstructive CB (n=22)
Personal smoking*
None	1	1	1
Past <20 pack-years	0.96 (0.49, 1.86)	1.27 (0.76, 2.12)	2.08 (0.13, 33.6)
Past >20 pack-years	2.11 (0.86, 5.14)	0.83 (0.28, 2.40)	9.67 (0.59, 160)
Current <20 pack-years	1.97 (0.98, 3.95)	1.30 (0.67, 2.51)	19.5 (2.13, 179)**
Current >20 pack-years	4.89 (2.73, 8.76)***	4.31 (2.58, 7.18)***	76.3 (9.56, 609)***
Asthma/wheezy breathing*
Never	1	1	1
Remitted	1.05 (0.56, 1.98)	0.71 (0.44, 1.14)	3.64 (0.42, 31.3)
Current	4.93 (2.68, 9.07)***	1.55 (0.93, 2.58)	20.6 (2.53, 167)**
Allergy history	1.12 (0.68, 1.84)	1.94 (1.24, 3.03)**	2.00 (0.66, 6.08)

Notes: Those with missing data were excluded from individual analyses.

a All exposure variables are adjusted for one another;

* Univariable P for trend across ordered groups <0.001;

** P<0.01;

*** P<0.001.

Abbreviations: CB, chronic bronchitis; CI, confidence interval; COPD, chronic obstructive pulmonary disease; OR, odds ratio.