Vitamin D deficiency is associated with impaired disease control in asthma–COPD overlap syndrome patients

INTRODUCTION: The association between vitamin D and clinical parameters in obstructive lung diseases (OLDs), including COPD and bronchial asthma, was previously investigated. As asthma–COPD overlap syndrome (ACOS) is a new clinical entity, the prevalence of vitamin D levels in ACOS is unknown. AIM: Our aim was to assess the levels of circulating vitamin D (25-hydroxyvitamin D [25(OH)D]) in different OLDs, including ACOS patients, and its correlation with clinical parameters. METHODS: A total of 106 men and women (control, n=21; asthma, n=44; COPD, n=21; and ACOS, n=20) were involved in the study. All patients underwent detailed clinical examinations; disease control and severity was assessed by disease-specific questionnaires (COPD assessment test, asthma control test, and modified Medical Research Council); furthermore, 25(OH)D levels were measured in all patients. RESULTS: The 25(OH)D level was significantly lower in ACOS and COPD groups compared to asthma group (16.86±1.79 ng/mL and 14.27±1.88 ng/mL vs 25.66±1.91 ng/mL). A positive correlation was found between 25(OH)D level and forced expiratory volume in 1 second (r=0.4433; P<0.0001), forced vital capacity (FVC) (r=0.3741; P=0.0004), forced expiratory flow between 25% and 75% of FVC (r=0.4179; P<0.0001), and peak expiratory flow (r=0.4846; P<0.0001) in OLD patient groups. Asthma control test total scores and the 25(OH)D level showed a positive correlation in the ACOS (r=0.4761; P=0.0339) but not in the asthma group. Higher COPD assessment test total scores correlated with decreased 25(OH)D in ACOS (r=−0.4446; P=0.0495); however, this was not observed in the COPD group. CONCLUSION: Vitamin D deficiency is present in ACOS patients and circulating 25(OH)D level may affect disease control and severity.