Lung function appears to continue to decline even decades after smoking cessation, according to new data from the National Heart, Lung, and Blood Institute Pooled Cohort. Compared with never-smokers, former smokers had a decline in forced expiratory volume in 1 second (FEV1) about 20% as severe as current smokers, but nevertheless higher than never-smokers. Low-intensity smokers also fared worse than never-smokers, suggesting that no amount of smoke exposure should be considered safe.
The increased decline occurred even decades after smoking cessation, according to the study published in, which was led by , of Columbia University, New York. Smoking prevalence has decreased from 42% to 16% in the past 50 years, and many smokers report that they smoke fewer cigarettes per day, from an average of 21 to 14, according to the authors. Despite those trends, the prevalence of chronic obstructive pulmonary disease has continued to increase, and is now the third-leading cause of death worldwide.
A meta-analysis of 47 studies and 88,887 adults found no association between smoking and FEV1 decline, but many of the studies were small or focused on nonrepresentative populations, and they used variably standardized spirometry.
The study pooled data from nine individual U.S. cohorts, with 25,352 participants recruited during 1983-2016. Subjects included those who underwent at least two prebronchodilator spirometry tests following American Thoracic Society. After adjustment, former smokers had increased FEV1 decline of 1.82 mL/year (P less than .0001), compared with never-smokers. Current smokers had an increased decline of 9.21 mL/year (P less than .0001).
Even after decades of abstinence, the effects of smoking appeared to linger: 20-30 years later, FEV1 loss was accelerated by 2.50 mL/year (P less than .0001), and by 0.93 mL/year (P = .0104) after 30 years, compared with never-smokers.
Even low-intensity smokers (cumulative less than 10 pack-years) had an significantly accelerated FEV1 decline (0.87 mL; P = .0153).
The researchers also found a relationship between FEV1 decline and intensity of current smoking: Those smoking fewer than 5 cigarettes per day had a lower decline than those smoking 30 or more (7.65 mL; 95% confidence interval, 6.21-9.09 vs. 11.24 mL; 95% CI, 9.86-12.62).
The study is limited by the fact that smoking status and daily tobacco reporting were self-reported, which could result in information bias.
The study was funded by the National Institutes of Health, National Heart Lung and Blood Institute, and U.S. Environmental Protection Agency. The authors report personal fees, consultancy fees, or grants from a wide variety of pharmaceutical companies.
SOURCE: Oelsner EC et al. Lancet Respir Med. 2019 Oct 9. .