Background: Previous studies on the relation of chronic bronchitis to incident airflow limitation and all-cause mortality have provided conflicting results, with positive findings reported mainly by studies that included populations of young adults. We sought to determine whether having chronic cough and sputum production in the absence of airflow limitation is associated with onset of airflow limitation, all-cause mortality, and serum levels of CRP and IL-8, and whether subjects’ age influences these relations.
Methods: We identified 1412 participants in the long-term Tucson Epidemiological Study of Airway Obstructive Disease who at enrollment (1972-73) were 21-80 years old and had FEV1/FVC≥70% and no asthma. Chronic bronchitis was defined as cough and phlegm production on most days for ≥three months in ≥two consecutive years. Incidence of airflow limitation was defined as the first follow-up survey with FEV1/FVC<70%. Serum IL-8 and CRP levels were measured in cryopreserved samples from the enrollment survey.
Results: After adjusting for covariates, chronic bronchitis at enrollment increased significantly the risk for incident airflow limitation and all-cause mortality among subjects <50 years old (Hazard Ratios, 95% CI: 2.2, 1.3-3.8; and 2.2, 1.3-3.8; respectively), but not among subjects ≥50 years old (0.9, 0.6-1.4; and 1.0, 0.7-1.3). Chronic bronchitis was associated with increased IL-8 and CRP serum levels only among subjects <50 years old.
Conclusions: Among adults <50 years old, chronic bronchitis unaccompanied by airflow limitation may represent an early marker of susceptibility to the effects of cigarette smoking on systemic inflammation and long-term risk for chronic obstructive pulmonary disease and all-cause mortality.