Socioeconomic Status and Prognosis of COPD in Denmark

Figures & data

Table 1.   Demographic and lifestyle variables of 6 590 individuals with COPD at baseline according to length of school education

	Length of school education
	< 8 yearsN = 1 590	8–10 yearsN = 3 131	> 10 yearsN = 1 244	UniversityN = 625	p value^1
Males,%	50	46	41	64	<0.001
Age, years (SD)	72 (8)	66 (11)	62 (13)	63 (13)	<0.001
Living alone,%	41	33	32	25	<0.001
High household income,%^2	2	14	30	56	<0.001
Smoking					<0.001
Never,%	14	18	24	28
Former,%	41	39	41	46
Current,%	45	43	35	27
Exposed to dusts and fumes at work,%	27	16	7	2	<0.001
Sedentary,%^3	12	10	7	7	<0.001
Fruit consumption ≥ 1 a day,%	45	50	58	59	<0.001
Vegetable consumption ≥ 1 a day,%	28	37	51	62	<0.001

¹p values were calculated using ANOVA for continuous variables and chi-square test for categorical variables.

²Defined as those belonging to the highest income tertile of all participants in The Copenhagen City Heart Study and The Copenhagen General Population Study, which corresponds to more than 80,000 Euros per year before taxation.

³Sedentary individuals were defined as individuals who only engaged in light physical activity as walking for less than 2 hours a week.

Table 2.  Disease characteristics of the 6 590 individuals with COPD at baseline according to length of school education

	Length of school education
	< 8 years N = 1,590	8–10 years N = 3 131	> 10 years N = 1 244	University N = 625	p value^1
FEV1,% pred (SD)	76 (21)	79 (19)	82 (18)	85 (18)	<0.001
mMRC > 2,%	28	18	12	9	<0.001
Chronic bronchitis,%	25	20	16	12	<0.001
Wheezing,%	32	30	24	18	<0.001
BMI, kg/m2 (SD)	26 (4)	26 (4)	25 (4)	25 (3)	<0.001
GOLD grouping					<0.001
A, N (%)	1,071 (67)	2,424 (77)	1,053 (85)	548 (88)
B, N (%)	318 (20)	444 (14)	126 (10)	41 (7)
C, N (%)	78 (5)	134 (4)	37 (3)	22 (4)
D, N (%)	123 (8)	129 (4)	28 (2)	14 (2)
On any inhaled medication,%	13	10	8	6	<0.001
On LABA, LAMA or ICS,%	9	7	6	5	0.001
On cardiac medication,%	15	9	8	8	<0.001

¹p values were calculated using ANOVA for continuous variables and chi-square test for categorical variables.

Abbreviations: mMRC: modified Medical Research Council Dyspnea scale, BMI: body mass index, GOLD: global initiative for obstructive lung disease, LABA: long-acting beta-2-agonist, LAMA: long-acting antimuscarinic agent, ICS: inhaled corticosteroid.

Table 3.  Five-year prognosis of the participants according to length of school education

	Length of school education
	< 8 yearsN = 1,590	8–10 yearsN = 3 131	> 10 yearsN = 1 244	UniversityN = 625	p value
COPD exacerbations, N (%)	231 (17.7)	328 (13.0)	88 (9.3)	37 (7.2)	<0.001
COPD admissions, N (%)	146 (11.8)	165 (7.2)	32 (3.3)	14 (2.6)	<0.001
All-cause mortality, N (%)	218 (17.6)	279 (12.3)	64 (7.7)	28 (5.7)	<0.001

All percentages are Kaplan-Meier estimates.

p values are based on log-rank trend test for time to event data.

Table 4.  The risk of exacerbations, hospital admissions and death during 5 years follow-up among participants with COPD according to level of school education

	Model 1Univariate^1	Model 2^2 Adjusted for variables defining GOLD A-D	Model 3^3 Adjusted for variables defining GOLD A-D and smoking	Model 4^4Adjusted for disease severity and other relevant confounders
	HR (95% CI)	HR (95% CI)	HR (95% CI)	HR (95% CI)
COPD exacerbations
<8 years	1.82 (1.28–2.59)	1.73 (1.22–2.47)	1.65 (1.15–2.37)	1.62 (1.10–2.37)
8–10 years	1.54 (1.09–2.16)	1.61 (1.14–2.27)	1.56 (1.10–2.22)	1.54 (1.06–2.23)
>10 years	1.24 (0.84–1.82)	1.45 (0.98–2.14)	1.41 (0.95–2.09)	1.40 (0.93–2.12)
University	1 (ref)	1 (ref)	1 (ref)	1 (ref)
COPD admissions
<8 years	2.65 (1.52–4.60)	1.89 (1.09–3.30)	1.74 (0.98–3.11)	1.55 (0.86–2.81)
8–10 years	1.99 (1.15–3.45)	1.66 (0.96–2.88)	1.60 (0.91–2.84)	1.41 (0.79–2.52)
>10 years	1.31 (0.70–2.46)	1.30 (0.69–2.45)	1.28 (0.67–2.45)	1.15 (0.60–2.22)
University	1 (ref)	1 (ref)	1 (ref)	1 (ref)
All-cause mortality
<8 years	2.19 (1.48–3.26)	1.89 (1.27–2.82)	1.96 (1.28–2.99)	1.86 (1.20–2.90)
8–10 years	1.92 (1.30–2.85)	1.79 (1.21–2.65)	1.89 (1.25–2.87)	1.90 (1.24–2.92)
>10 years	1.51 (0.96–2.36)	1.42 (0.91–2.24)	1.51 (0.94–2.42)	1.50 (0.93–2.42)
University	1 (ref)	1 (ref)	1 (ref)	1 (ref)

¹Adjusted for age (underlying time scale) and sex.

²Adjusted for age, sex and FEV₁%pred., mMRC, frequent exacerbations, the latter three included as binary variables defined according to GOLD A-D.

³Adjusted for variables in model 2 and smoking (never smoker, former smoker and current smoker).

⁴Adjusted for age, sex, FEV₁%pred. (continuous), mMRC (groups 0-4), exacerbations (at least 2 vs. less than 2 last year), smoking (never smoker, former smoker and current smoker), former or current substantial exposure to dust and fumes at work (yes vs. no), dietary intake of vegetables (at least 1 vs. less than 1 a day), cohabitation (cohabitating with a partner vs. living alone), use of inhaled medication (yes vs. no), use of cardiac medication (yes vs. no), BMI (4 groups according to World Health Organisation), and daily cough and sputum (yes vs. no).