Lung disease and asthma severity in adults with asthma: data from the Third National Health and Nutrition Examination.

Risk factors for obstructive or restrictive lung disease among persons with asthma are not well defined. Data from the Third National Health and Nutrition Examination Survey were used to determine predictors of poor lung function among 1063 adults, aged 20 years and older, who self-report physician-diagnosed asthma any time during their life regardless of current asthma status. Obstructive lung disease and restrictive lung disease were defined by using spirometry and modified Global Initiative for Chronic Obstructive Lung Disease criteria. Reported symptoms were used to grade asthma severity. Logistic regression models were used to examine associations between lung disease, respiratory symptom severity, and adults who ever had asthma. Risk factors for spirometry-defined obstructive lung disease included increasing age, body mass index < 18.5, current asthma, and non-white race (p < 0.05). Risk factors for spirometry-defined restrictive lung disease included older age at asthma diagnosis, low socioeconomic status, current asthma, and being female (p < 0.05). Risk factors for moderate or severe respiratory symptoms included older age at diagnosis and current smoking status (p < 0.05). Asthma is a known risk factor for chronic obstructive lung disease; these data also suggest that adults, particularly females, who are older at the time of asthma diagnosis, may be at risk to develop spirometry-defined restrictive lung disease as well. These data also suggest that a significant proportion of people with lifetime asthma have impaired lung function; however, it is unclear if more aggressive therapy for asthma would prevent these complications. To further examine the role of these factors in predicting poor lung function among adults with asthma, additional information is needed on these patients' asthma therapy, natural history, and environmental exposures.