Adults with persistent asthma, defined as per the Global INitiative for Asthma Management (GINA) criteria, and specifically with positive bronchodilator test, or a daily peak expiratory flow (PEF) variability greater than 20%, or a positive methacholine challenge test documented in case history. Subjects were consecutively enrolled from the outpatient visits of a specialized Asthma Unit located in a tertiary University Hospital.