Risk factors for chronic obstructive pulmonary disease in never‐smokers: A systematic review

INTRODUCTION: Relatively little is known about the risk factors for chronic obstructive pulmonary disease (COPD) in never‐smokers, and these factors have not yet been fully characterised. This study therefore sought to analyse COPD risk factors in never‐smokers by conducting a systematic review of the literature on the topic. MATERIALS AND METHODS: We performed a search in PubMed (Medline) and Embase from 2000 onwards, to locate studies on COPD in never‐smokers. For literature search and evidence synthesis purposes, we used the PRISMA guidelines and drew up a specific quality scale to quantify the evidence of each study included. RESULTS: The bibliographic search retrieved a total of 557 papers, 20 of which fulfilled the designated inclusion criteria (two case–control studies, four cohort studies and 14 cross‐sectional studies). These studies were undertaken in Europe, the United States, Latin America, Asia and Africa. The risk factors for never‐smokers were varied and ranged from exposure to biomass, occupational exposure and passive smoking to having a history of asthma, tuberculosis or respiratory infections during childhood. The effect of residential radon was unclear. The highest risk was obtained for previous respiratory diseases of any type, with a magnitude much higher than that observed for other risk factors. CONCLUSIONS: There are few studies on COPD risk factors in never‐smokers. More purpose‐designed studies in this subpopulation are thus called for, including well‐designed studies to specifically assess if indoor radon has any role on COPD onset.