Body mass index, weight gain, and other determinants of lung function decline in adult asthma.

Background: Little is known about factors associated with lung function decline in asthma.
Objective: To identify the determinants of FEV(1) decline in adults with asthma with and without airflow obstruction at baseline.
Methods: An international cohort of 638 subjects with asthma (20-44 years old) was identified in the European Community Respiratory Health Survey (1991-1993) and followed up from 1998 to 2002. Spirometry was performed on both occasions. FEV(1) decline was related to potential determinants evaluated at baseline and during the follow-up by random intercept linear regression models. The analyses were stratified by the presence of airflow obstruction (FEV(1)/forced vital capacity < 0.70) at baseline.
Results: In the group of individuals without airflow obstruction (n = 544), a faster FEV(1) decline was observed for subjects with intermediate body mass index (BMI) than for lean and obese subjects. FEV(1) decline was associated with weight gain independently of baseline BMI, and this association was stronger in men (20; 95% CI, 10-30, mL/y/kg gained) than in women (6; 95% CI, 1-11, mL/y). In the group of individuals with airflow obstruction (n = 94), the absence of allergen sensitization and a low BMI at baseline were associated with a faster FEV(1) decline, whereas weight gain was not associated with decline.
Conclusions: The detrimental effect of weight gain on FEV(1) decline is particularly relevant in subjects with asthma who still do not have an established airflow obstruction. Our findings support the importance of weight management in asthma and recommend weight loss in overweight or obese individuals with asthma.