FIGURE 1.

Flow diagram of study participants. This flow diagram depicts the screening and randomization of participants for the study. The numbers of participants excluded because of supplement use or high vitamin D concentrations are not generalizable, because a large part was already prescreened by their physicians at the outpatient clinic or during hospital admission. COPD, chronic obstructive pulmonary disease; FEV₁, forced expiratory volume in 1 s; ITT, intention-to-treat; IU, International Unit; 25(OH)D, 25-hydroxyvitamin D.