KEYSTONE, COLO. — Obesity appears to be modestly associated with subsequent development of asthma, particularly in women, Dr. David A. Beuther reported at a meeting sponsored by the National Jewish Medical and ResearchCenter.
His metaanalysis of data from the Nurses' Health Study and six other large prospective studies totaling well over 200,000 subjects with 2- to 10-year follow-up concluded that women who became overweight or obese were 68% more likely to develop asthma within 1 year than those who maintained a body mass index (BMI) below 25 kg/m
In men, a BMI greater than 25 was associated with a 46% increase in incident asthma in 1 year, according to Dr. Beuther of the Denver center.
All seven of the prospective studies showed a positive relationship between obesity and asthma. In many of the studies, the relationship didn't achieve statistical significance; however, when the data were pooled, the results became highly significant.
A major caveat regarding the putative obesity-asthma link is that most studies to date have relied on self-reported asthma or physician-diagnosed asthma without confirmatory pulmonary testing. The question arises: Do these heavy patients truly have asthma, or do they merely develop asthmalike symptoms of wheezing and shortness of breath due to obesity-induced chest wall restriction?
Dr. Beuther is conducting a bronchoscopic study designed to answer this question, as well as to better characterize the airway inflammation present in obese asthmatic patients. He has found that many obese patients who carry the diagnosis of asthma don't actually have the disease upon rigorous testing.
And yet the obesity-asthma relationship certainly has biologic plausibility. Obesity is at its essence a systemic inflammatory state. Receptors for leptin, a proinflammatory cytokine produced by adipocytes, are found in the lungs. It is possible that the upregulated systemic inflammatory state of obesity spills over to contribute to airway inflammation and asthma.
A couple of relatively small studies in asthmatic children are supportive. In one, 23 asthmatic children were found to have higher leptin levels than controls—and their leptin levels dropped to that of controls within several weeks after going on inhaled corticosteroid therapy (Ann. Allergy Asthma Immmunol. 2004;93:277–80). And in a study of 102 asthmatic children, elevated leptin was associated with a twofold increased prevalence of asthma. Atopic asthmatics had significantly higher leptin levels than nonatopic asthmatics (J. Allergy Clin. Immunol. 2004;114:254–9).
In addition, recent preliminary data suggest obesity and asthma share four chromosome loci, Dr. Beuther continued.
Assuming obesity is an independent risk factor for asthma, it is reasonable that obese asthmatics who lose weight should experience improvement in their respiratory disease. The single randomized, controlled, 38-patient study of medical weight loss and asthma performed to date showed a positive correlation.
Many obese patients who carry the diagnosis of asthma don't actually have the disease upon rigorous testing. DR. BEUTHER
