Low smoking exposure and development and prognosis of COPD over four decades: A population-based cohort study.

A diagnosis of chronic obstructive pulmonary disease (COPD) is mainly considered in individuals with more than 10 pack-years of smoking. We tested the hypothesis that low smoking exposure, below the critical threshold of 10 pack-years, increases risk of COPD and leads to poor prognosis.We followed non-obstructive adult smokers from the Copenhagen City Heart Study for COPD, defined as forced expiratory volume in one second [FEV 1 ]/forced vital capacity [FVC]<0.70 and FEV 1 <80% predicted, and for related clinical outcomes. First, we followed individuals for 5years according to baseline smoking for risk of developing COPD, and hereafter for up to four decades for severe exacerbations and death.In 6098 non-obstructive smokers, 1781(29%) developed COPD after 5 years follow-up; 23% in individuals with <10pack-years of smoking at baseline, 26% in those with 10-19.9pack-years, 30% in those with 20-39.9pack-years, and 39% in those with ≥40pack-years. During four decades follow-up, we recorded 620 exacerbations and 5573 deaths. Compared to individuals without COPD with <10pack-years of smoking, multivariable adjusted hazard ratios (HRs) for exacerbations were 1.94(95% confidence interval:1.36-2.77) in those without COPD with ≥10pack-years, 2.83(1.72-4.66) in those with COPD with <10pack-years, 4.34(2.93-6.43) in COPD with 10-19.9pack-years, 4.39(2.98-6.47) in COPD with 20-39.9pack-years, and 4.98(3.11-7.97) in COPD with ≥40pack-years. Corresponding HRs for all-cause mortality were 1.20(1.10-1.32), 1.33(1.14-1.56), 1.59(1.40-1.80),1.81(1.62-2.03), and 1.81(1.55-2.10), respectively.Low smoking exposure below the critical threshold of 10 pack-years increases risk of COPD in middle-aged adults within 5 years, and these individuals have increased risk of severe exacerbation and early death over four decades.