Lung function decline in former smokers and low-intensity current smokers

Lung function decline in former smokers and low-intensity current smokers
Kyle Walburg, PharmD, North Memorial Camden Clinic

Background:With more medications for smoking cessation and increased public attention to quitting, there are now more former smokers than current smokers in many developed countries. Overall, current smokers are smoking less cigarettes per day. Studies regarding ongoing lung function decline after quitting yield mixed outcomes; some suggest lung function normalizes after cessation, while others suggest that mechanistically, lung damage could continue. 

Objective:This study hypothesized that former smokers and current low-intensity smokers (less than five cigarettes per day) have increased lung function decline as compared to never smokers, including those without prevalent lung disease. 

Study Design:Information from six United States population-based cohorts included in the National Heart, Lung, and Blood Institute (NHLBI) Pooled Cohort Study was used in this analysis. Included patients were required to have at least two separate spirometry exams, as validated by American Thoracic Society (ATS) standards; exams were performed between 1983 and 2014. Cohorts included younger adults (17 years and older), middle-aged and older adults (45 years and older), and elderly adults (65 years and older). Lung function decline was measured using forced expiratory volume (FEV1) and compared between former smokers, current smokers, and never smokers. Results were adjusted for sociodemographic and anthropometric factors. FEV1 was also examined with regard to the amount of time elapsed since quitting, cumulative pack years, and current number of cigarettes smoked.

Results: The analysis included 25,432 participants that received at least two valid spirometry exams over the data collection period. Median age of participants was 57 years; FEV1 decline at this median age was  31.01 ml per year [95% CI 30.66-31.37] for never smokers, 34.97 ml per year [95% CI 34.36-35.57] for former smokers, and 39.92 ml per year [95% CI 38.92-40.92] in current smokers. When these results were adjusted for former smokers, it was shown that FEV1 decline was accelerated when comparing former smokers to never smokers; the accelerated decline was 20% that of current smokers. Accelerated decline persisted in participants who had quit decades prior and in current smokers with less than ten cumulative pack years. Low-intensity smokers (less than five cigarettes per day) had 68% that of current smokers smoking 30 or more cigarettes per day, and five times higher than smokers that had successfully quit. It was unclear from the results of this study and other supporting literature if FEV1 decline decelerates or returns to that of a never smoker after successfully quitting; however, results suggested an accelerated rate of FEV1 decline persisted decades after quitting smoking.

Conclusions: Smokers that use less than five cigarettes per day or have successfully quit smoking have faster lung function decline compared to those who had never smoked. Importantly, this offers additional evidence about ongoing lung function decline that persists even after quitting smoking. While significant decreases in cigarettes smoked did decrease this rate of decline, even less than five cigarettes per day led to considerable acceleration in lung function decrease. Regardless of if smokers completely quit or decrease their consumption, the results of this study suggest that damage is ongoing and lasting, and progressive lung disease likely occurs. The results of this study help solidify the recommendation that there is no safe level of tobacco smoke exposure, and that smoking cessation is the most efficacious method of harm reduction. 

The results can be used to support motivational interviewing performed by pharmacists to influence those attempting to quit smoking. Additionally, the study shows the importance of offering comprehensive care to former smokers, as their risk for ongoing lung decline persists decades after quitting.

Key Point:Former smokers and those smoking less than five cigarettes per day experience faster lung function decline than never smokers. Pharmacists are in a unique position to use results from this study to help facilitate smoking cessation reduce harm.


  1. Oelsner EC, Balte PP, Bhatt SP, et al. Lung function decline in former smokers and low-intensity current smokers: a secondary data analysis of the NHLBI Pooled Cohorts Study. Lancet Respir Med. 2019 Oct 9. pii: