Smoking reduction and cessation reduce chronic cough in a general population: the Inter99 study

Background: Chronic cough can be the first sign of chronic obstructive disease. A few, and mostly selected, studies exploring the effect of reduced daily tobacco consumption have shown a small effect on pulmonary symptoms. Aim: The aim of this study was to examine if smoking reduction (SR) (>= 50% of daily tobacco consumption) or smoking cessation (SC) had an effect on chronic cough and phlegm. Methods: A total of 2408 daily smokers were included in a Danish population-based intervention study, Inter99. In the analyses, we included smokers with self-reported chronic cough or phlegm at baseline who also attended the 1-year follow-up. We investigated if SR or SC had improved the self-reported pulmonary symptoms, using logistic regression analyses. Results: Almost 34% of the smokers had chronic cough at baseline and 24.5% had chronic phlegm. Thirty-seven persons with cough at baseline and 24 with phlegm at baseline achieved substantial SR at 1-year follow-up. The corresponding numbers for SC were 63 and 39, respectively. In adjusted analyses, quitting or reducing smoking was associated with less reporting of cough [odds ratio (OR): 14.2; 95% confidence interval (CI): 5.9-34,4] and (OR: 3.7; 95% CI: 1.7-8.0), respectively, compared with unchanged smoking habits. It was also significantly more likely not to report phlegm at 1-year follow-up for those who had quit (OR: 7.1; 95% CI: 2.8-18.0), whereas SR was not significantly associated with termination of phlegm (OR: 2.5; 95% CI: 0.9-6.4) when compared with continuous smoking. Conclusion: SC significantly improved self-reported chronic cough and phlegm as expected. Substantial SR was achieved by few smokers but had a significantly positive effect on chronic cough.