Background: Previous studies on the relationship 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. This study 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 C-reactive protein (CRP) and interleukin-8 (IL-8), and whether subjects’ age influences these relationships.
Methods: 1412 participants in the long-term Tucson Epidemiological Study of Airway Obstructive Disease who at enrolment (1972–1973) were 21–80 years old and had FEV1/FVC (forced expiratory volume in 1 s/forced vital capacity) ⩾70% and no asthma were identified. Chronic bronchitis was defined as cough and phlegm production on most days for ⩾3 months in two or more 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 enrolment survey.
Results: After adjusting for covariates, chronic bronchitis at enrolment significantly increased the risk for incident airflow limitation and all-cause mortality among subjects <50 years old (HR 2.2, 95% CI 1.3 to 3.8; and HR 2.2, 95% CI 1.3 to 3.8; respectively), but not among subjects ⩾50 years old (HR 0.9, 95% CI 0.6 to 1.4; and HR 1.0, 95% CI 0.7 to 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.
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Funding This study was funded by grants HL14136 and HL085195 from the National Heart, Lung, and Blood Institute, a grant award by the American Thoracic Society/Alpha1 Foundation, grant 0660059Z by the American Heart Association, and an unrestricted grant from the Barry and Janet Lang Donor Advised Fund. SG is the recipient of a Parker B Francis Fellowship.
Competing interests None.
Provenance and Peer review Not commissioned; externally peer reviewed.
Ethics approval Ethics approval was obtained from the University of Arizona Institutional Review Board.
▸ Additional data, including tables and a figure, are published online only at http://thorax.bmj.com/content/vol64/issue10
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