Quitting smoking is the most important step smokers can take to improve their health. Nonetheless, there is little information on long-term improvements in lung function and/or respiratory symptoms after smoking cessation. Here we illustrate long-term changes in spirometric indices as well as in respiratory symptoms in smokers invited to quit or reduce their cigarette consumption by switching to electronic cigarettes (ECs). Prospective evaluation of cigarette consumption, spirometry and symptoms was performed in a 1-year randomized controlled trial of smokers receiving EC containing 2.4%, 1.8% or 0% nicotine. Spirometric data are presented on the basis of participants’ pooled continuous smoking phenotype classification (Quitters, Reducers, Failures), whereas respiratory symptoms on the basis of their point prevalence-smoking phenotype. Smoking phenotype classification (Quitters, Reducers, Failures) had no significant effect on spirometric indices (FEV1, FVC and FEV1/FVC) with the exception of FEF25–75%, which significantly (P  =0.034) increased over the time among Quitters; their FEF25–75% (% predicted) improving from (means±S.D.) 85.7±15.6% at baseline (BL) to 100.8±14.6%. High prevalence of cough/phlegm (43.1%) and shortness of breath (SoB; 34.8%) was reported at BL with substantial reduction in their frequency at subsequent follow-up visits. These symptoms virtually disappeared very quickly in both quitters and reducers. Smokers invited to switch to ECs who completely abstained from smoking showed steady progressive improvements in their FEF25–75%. Normalization of peripheral airways function was associated with improvement in respiratory symptoms, adding to the notion that abstaining from smoking can reverse tobacco harm in the lung.

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