The relation of body mass index to asthma, chronic bronchitis, and emphysema.
BACKGROUND
Recent studies have suggested a relationship between asthma and obesity. Despite these reports, the effect of being underweight or overweight as a risk factor for airway obstructive diseases (AODs) is not clear.


OBJECTIVE
To determine whether a relation of body mass index (BMI) to asthma, chronic bronchitis (CB), or emphysema exists (analysis 1), and, if so, whether the association between obesity and asthma is modified by gender (analysis 2).


METHODS
Nested case-control study from the longitudinal cohort of the Tucson Epidemiologic Study of Airways Obstructive Diseases.


METHODS
Analysis 1: physician-confirmed incident cases of asthma (n = 102), CB (n = 299), or emphysema (n = 72) who denied any prior AODs. Analysis 2: all 169 incident cases of asthma, regardless of any previous AODs, stratified by gender and by other potential effect modifiers. In both analyses, we selected only subjects at least 20 years old who had weight and height measured during the study.


METHODS
BMI and other risk factors were assessed prior to the onset of the AOD (cases) or prior to the last completed survey (control subjects).


RESULTS
A diagnosis of emphysema was significantly associated with a BMI < 18.5 (odds ratio [OR], 2.97; 95% confidence interval [CI], 1.33 to 6.68, when compared to healthy control subjects). A BMI >/= 28 increased the risk of receiving a diagnosis of asthma (OR, 2.10; 95% CI, 1.31 to 3.36) and CB (OR, 1.80; 95% CI, 1.32 to 2.46). About 30% of the patients with asthma and 25% of the patients with CB (vs 16% of the control subjects, p < 0.001) were preobese or obese, regardless whether BMI was assessed before the diagnosis or before the onset of respiratory symptoms. The relation of elevated BMI to asthma was significant only among women.


CONCLUSIONS
Patients with emphysema are more likely to be underweight, and patients with CB are more likely to be obese. However, the temporal relationship between abnormal BMI and the onset of COPD is uncertain. Preobese and obese women are at increased risk of acquiring asthma. This relation, particularly if it is causal, has potentially relevant public health implications.
Guerra
Stefano
S
Arizona Respiratory Center, College of Medicine, University of Arizona, 1501 N. Campbell Avenue, Tucson, AZ 85724-5030, USA.
Sherrill
Duane L
DL
Bobadilla
Arnel
A
Martinez
Fernando D
FD
Barbee
Robert A
RA
D000328:Adult; D017677:Age Distribution; D000368:Aged; D001249:Asthma / Q000175:diagnosis / Q000453:epidemiology*; D015992:Body Mass Index; D029481:Bronchitis, Chronic / Q000175:diagnosis / Q000453:epidemiology*; D016022:Case-Control Studies; D015331:Cohort Studies; D015897:Comorbidity; D016001:Confidence Intervals; D005260:Female; D006801:Humans; D015994:Incidence; D007558:Italy / Q000453:epidemiology; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D009765:Obesity / Q000175:diagnosis / Q000453:epidemiology*; D016017:Odds Ratio; D011379:Prognosis; D011656:Pulmonary Emphysema / Q000175:diagnosis / Q000453:epidemiology*; D012129:Respiratory Function Tests; D012307:Risk Factors; D012720:Severity of Illness Index; D017678:Sex Distribution