Correlation analysis of continuous variables associated with baseline concentrations of serum 25(OH)D.

#<p>BMI: Body mass index.</p>§<p>PaO₂: Arterial oxygen tension.</p

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

§<p>BMI: body mass index.</p>*<p>FEV₁: Forced expiratory volume in 1 s.</p>##<p>Season was defined as winter (December-March), spring (April-May), summer (June-September), and autumn (October–November).</p>#<p>Exacerbations requiring either hospitalisation or treatment with oral antibiotics or oral steroids.</p>§§<p>PaO₂: arterial oxygen tension.</p>**<p>Associations were tested with t-test and Chi-square.</p

Coefficients from multiple linear regression and logistic regression models, showing the relationship between baseline predictors and serum levels of 25(OH)D in COPD patients.

*<p>For both the linear and logistic regression models a backward stepwise procedure was used with the following variables included at start: Age, sex, GOLD status, hypoxemia (resting PaO₂<8), dyspnea (grade III), inhaled steroids, ICS (yes or no), *body mass index (BMI), comorbidity (Charlsons score <2 or ≥2), total white blood count, treatment for osteoporosis (yes or no), depression (CES-D score≥16) and exacerbation frequency (≥2 last year; yes or no).</p>#<p>Season was defined as winter (December–March), spring (April–May), summer (June–September), and autumn (October–November).</p