We analyzed Lung Health Study (LHS) data to assess the effect of self-reported lower respiratory illnesses resulting in physician visits (LRI) on lung function. Participants were 5,887 smokers aged 35–60 yr, FEV₁/ FVC < 0.70 and FEV₁ of 55–90% predicted. Two-thirds were randomized into an intensive smoking cessation program (SI); one-third were advised only to stop smoking (UC). For 5 yr participants had annual spirometry and questioning regarding LRI. SI had greater rates of smoking cessation than usual care (UC) with fewer LRI (p = 0.0008). Sustained quitters had fewer LRI than continuing smokers (p = 0.0003). In the year LRI occurred, FEV₁ did not change in sustained quitters, but decreased significantly in smokers (p = 0.0001) with some recovery the following year if no LRI occurred. Over 5 yr, LRI had a significant effect on rate of decline of FEV₁ only in smokers. In smokers averaging one LRI/yr over 5 yr there were additional declines in FEV₁ of 7 ml /yr (p = 0.001). Smokers with more than one LRI / yr had greater declines. Chronic bronchitis was associated with increased frequencies of LRI, but did not affect their influence on lung function. Smoking and LRI had an interactive effect on FEV₁ in people with mild COPD, and in smokers frequent LRI may influence the long-term course of the disease.

Keywords: smoking; chronic obstructive pulmonary disease; lower respiratory infections; chronic bronchitis