Electronic cigarette use in relation to changes in smoking status and respiratory symptoms.

"CONFLICTS OF INTEREST The authors have each completed and submitted an ICMJE form for Disclosure of Potential Conflicts of Interest. The authors declare that they have no competing interests, financial or otherwise, related to the current work. H. Backman reports personal fees for lectures from AstraZeneca, Sanofi, and GlaxoSmithKline. H. Kankaanranta reports personal fees for consultancies or lectures from AstraZeneca, Boehringer-Ingelheim, Chiesi Pharma, GSK, MSD, Mundipharma, Novartis, Orion Pharma and SanofiGenzyme. A. Lindberg reports personal fees for lectures and advisory board from Boehringer Ingelheim, Novartis, AstraZeneca, and GlaxoSmithKline. C. Stridsman reports personal fees for lectures and advisory board from Boehringer Ingelheim, Novartis, and AstraZeneca."

"FUNDING This work was supported by The Swedish Heart Lung Foundation, The Swedish Asthma and Allergy Foundation, VBG Group Herman Krefting Foundation for Asthma and Allergy Research, Swedish Research Council, ALF: a regional agreement between Umeå University and Region Västerbotten, and University of Gothenburg and Region Västra Götaland, respectively; Norrbotten County council and VISARE NORR Fund: Northern county councils’ Regional federation. None of the funding sources had any role in the design of the study and collection, analysis, and interpretation of data, in the writing of the report, or in the decision to submit the article for publication."