Quitting Smoking, Not Cutting Back, Linked to Better Lung Health

Smokers who quit had lower disease risk than the group identified as stable, low-rate smokers.

Amanda Mathew, PhD

In a longitudinal, population-based study, researchers identified a dose-response relationship between smoking exposure, lung function decline and lung disease risk, concluding that long-term light smokers present at greater risk for lung function decline, emphysema and obstructive lung disease than heavy smokers who quit.

The new research, presented at the 2018 American Thoracic Society International Conference, was a compilation of analyzed data collected over 30 years from 3140 participants in the Coronary Artery Risk Development in Young Adults (CARDIA) study who completed yearly assessments of smoking behavior and spirometry measurements at years 0, 2, 5, 10, 20 and 30. Participants, when enrolled, lived in 4 US cities—Birmingham, Ala., Chicago, Ill., Minneapolis, Minn., and Oakland, Calif.

Patient characteristics included an average age of 25 years, were predominantly female (57.3%), 47.7% African American, and about 47.9% endorsed lifetime smoking. Additionally, patients underwent periodic spirometry to assess lung function and chest CT scans 15, 20 and 25 years after enrolling.

“The CARDIA dataset gave us a unique opportunity to learn about the impact of different levels of smoking on lung health and lung disease risk,” lead author, Amanda Mathew, PhD, research assistant professor, Northwestern University Feinberg School of Medicine, said. “Participants were asked about their smoking each year, which minimized recall bias and allowed us to model changes in smoking habits over time.

Study outcomes included loss of lung health (decline in forced expiratory volume in 1 second (FEV1) from peak) and incident lung disease (emphysema on year 24 thoracic CT and obstructive physiology at year 30).

Researchers identified 6 smoking trajectory groups: declining heavy (n = 58), stable heavy (n = 200), stable moderate (n = 237), quitters (n = 199), stable low rate ( <10 pack-years) (n = 228), minimal/non-smokers (n = 582), and never smokers (n = 1636).

After adjusting for age, sex, race, body mass index, asthma and baseline smoking status, smoking trajectory groups were differentially associated with lung function decline and disease risk.

Results showed that stable heavy smokers showed the greatest decline in FEV1 (-42.2 mL/year) and disease risk relative to non-smokers, with nearly 8 times the odds of obstructive disease (OR 7.7, CI 4.1—14.7) and 26 times more likely to develop emphysema (OR= 24.1, CI 12.6–46.2).

When comparing lung health outcomes within 2 low-intensity smoking groups, stable low rate smokers and quitters, the quitter population showed less FEV1 decline, preserving more lung function (-33.8 mL/year vs. -35.7 mL/year) and had a lower risk of developing emphysema (OR= 2.8, CI 1.2&shy;—6.3 vs. OR= 7.7, CI 4.2–14.2) despite having a greater pack-year history (9.8 vs. 6.4). For both groups, the number of years smoking was superior to lifetime pack-years in predicting risk of emphysema.

Researchers concluded that smoking duration was a better predictor of emphysema risk than smoking intensity, which demonstrates the effects of long-term smoking, regardless of smoking amount.

Study limitations include not being able to adjust for secondhand smoke, marijuana smoke or e-cigarette smoke.

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