Table 1. Baseline characteristics of the study sample, presented as mean±sd for continuous and percentage for categorical variables.

	COPD	Controls	p**
Subjects, n	433	325
Sex, % females	40	46	0.11
Age, years	63.5±6.9	58.6±9.8	<0.001
Smoking habits:			<0.001
Never	0	14
Ex	56	32
Current	44	54
BMI § (kg/m2)			<0.001
<18.5	8	0.5
18.5–24.9	43	39
25–30	35	45.5
>30	14	16
Comorbidity, Charlsons score			<0.001
0	0	70
1	58	22
2	23	6
3	12	2
4	7	0
Depression, CES-D score≥16			<0.001
Yes	21	6
Season #			<0.001
Winter	16	31
Spring	21	41
Summer	56	2
Autumn	7	26
FEV1 in percent predicted *	49±14	102±10	<0.001
GOLD status:
II (FEV1 50–80)	46
III (FEV1 30–50)	42
IV (FEV1 0–30)	12
Resting PaO2 §§	9.3±1.2
Hypoxemia, % yes	12
Symptoms, % yes
Cough with phlegm	59
Dyspnea (grade III)	44
Inhaled steroids, ICS, % yes	69
Exacerbations ## :
<2 last 12 months	83
≥2 last 12 months	17
Total white blood count	8.1±2.2
Vitamin D, 25(OH)D			0.86
<20 ng/mL	33	34
≥20 ng/mL	67	66

^§BMI: body mass index.

^*FEV₁: Forced expiratory volume in 1 s.

^##Season was defined as winter (December-March), spring (April-May), summer (June-September), and autumn (October–November).

^#Exacerbations requiring either hospitalisation or treatment with oral antibiotics or oral steroids.

^§§PaO₂: arterial oxygen tension.

^**Associations were tested with t-test and Chi-square.