Study objective: To investigate the risk of COPD among nonsmokers.
Design: Case-control study, logistic regression analysis.
Setting: Third National Health and Nutrition Examination Survey, from 1988 to 1994.
Participants: Community residents 18 to 80 years of age, of white, black, or Mexican-American ethnicity. Nonsmokers included never-smokers and former smokers with a < 5 pack-year smoking history who had never smoked cigars or pipes.
Measurements: COPD (FEV1/FVC < 70%) was classified as mild (FEV1 > or = 80% predicted) or moderate to severe (FEV1 23 to 79% predicted).
Results: Among 13,995 examinees, 51.3 +/- 0.4% were female, mean age was 42.2 +/- 0.4 years, 48.7 +/- 0.9% were nonsmokers, 8.8 +/- 0.3% had mild COPD, and 4.1 +/- 0.3% had moderate-to-severe COPD [+/- SE]. One fourth of mild and moderate-to-severe cases were nonsmokers. Among 7,526 nonsmokers, 4.7 +/- 0.3% had mild COPD (n = 403; age, 60.9 +/- 1.3 years) and were mostly female (82.5%), while 1.9 +/- 0.3% had moderate-to-severe COPD (n = 92, age 39.3 +/- 1.3) and were mostly male (88.1%). Few nonsmokers with COPD (12.1 +/- 2.4%) had a previous diagnosis of chronic bronchitis or emphysema. Among nonsmokers, physician-diagnosed asthma increased the risk of mild and especially of moderate-to-severe COPD. Independently of asthma, risk of mild COPD in nonsmokers increased with age (doubling every 12 years), before age 60 was lower among men than women, and was inversely associated with current exposure to tobacco smoke at home and at work. In contrast, the risk of moderate-to-severe COPD in nonsmokers was markedly associated with male gender, peaked in middle age, and was inversely associated with nonwhite ethnicity. COPD risks did not vary by minimal smoking history, longest-held occupation, urban residence, income, allergies, thyroid disease, or Helicobacter pylori antibody.
Conclusions: Among nonsmokers, mild and moderate-to-severe COPD are associated with asthma but otherwise have distinct demographic profiles, suggesting that moderate-to-severe disease is not a mere progression of mild COPD.