There is evidence that iron plays a key role in the adequate functioning of skeletal muscle. While it has been demonstrated that nonanemic iron deficiency (NAID) affects exercise tolerance and response to exercise training in patients with COPD, the impact on daily physical activities (DPAs) remains unknown. Eighteen COPD patients with NAID (ferritin <100 ng/mL or ferritin 100-299 ng/mL with a transferrin saturation <20%) and 18 COPD patients without this abnormality, matched for age, gender, and the degree of airflow limitation (control group), were enrolled to the study. The primary outcome was the level of DPA assessed by accelerometers. Patients were (mean [SD]) 66 (7) years and were mostly male (70%) and former smokers (52%). Their forced expiratory volume at 1 second was 41 (16)% predicted, carbon monoxide diffusing capacity was 47 (14)% predicted and oxygen arterial pressure reached 70 (11) mmHg. DPA and the number of steps per day were lower in NAID COPD patients compared with controls (physical activity level 1.39 vs 1.59, P<0.05; and 4,402 vs 6,975 steps/day, P<0.05, respectively). The percentage of patients with increased time spent sitting per day (>6 hours) was higher in patients with NAID compared with controls (73% vs 37%, P<0.05). In addition, the percentage of patients doing moderate to vigorous physical activity per day (>3 metabolic equivalents of task, at least 30 minutes) was lower in this group (66% vs 100%, P<0.05). The presence of iron deficiency was associated with reduced DPA in COPD patients. Further studies are needed to evaluate iron reposition and their impact on the level of physical activity in these patients.

The authors would like to thank Ana Balañá, Concepción Ballano, and Laura Gutiérrez for their assistance in collecting the data for this study. They want to acknowledge the support of the Instituto de Salud Carlos-III (FIS 14/00713 [FEDER], FIS 18/00075 [FEDER], FIS 17/00649 [FEDER], and BA 17/00025), CIBERES (ESF02/2017), Spanish Respiratory Society (SEPAR) 2016 and 2017 (409/2017), Catalan Foundation of Pulmonology (FUCAP) 2016 and 2017, Catalan Respiratory Society (SOCAP) 2017, Ministerio de Economía y Competitividad (SAF2014-54371 [FEDER]), Menarini (2015–2018), and Vifor Pharma (2017–2018).