HONOLULU – A large, long-term study suggests that obesity is significantly associated with airway hyperresponsiveness, and therefore it might be a risk factor for asthma.
"There is definitely a relationship between obesity and the risk of having airway hyperresponsiveness, and maybe asthma," lead investigator Dr. Manon Labrecque said during an interview in advance of annual meeting of the American College of Chest Physicians, where the study was presented during a poster session.
Dr. Manon Labrecque
"But how is it mediated? What is the explanation? It seems to be related to the mechanical effect of obesity on the volume of the lungs, [but] some other analysis of the data will permit us to better understand," Dr. Labrecque said.
The investigators reviewed the medical records of 17,195 patients with a mean age of 48 years who were referred to the Hôpital du Sacré-Coeur de Montréal, Canada, for confirmation of an asthma diagnosis between 1980 and 2000.
They then analyzed the data in order to classify patients as having obesity class 1 (body mass index of 30-34.9 kg/m2), class 2 (BMI of 35-39.9 kg/m2), or class 3 (BMI more than 40 kg/m2), and compared them with normal-weight patients (those with a BMI between 18.5 and 25 kg/m2). To define airway hyperresponsiveness, the study used a standard criterion: methacholine challenge cutoff of less than 8 mg/mL for causing a 20% fall in FEV1 (forced expiratory volume in 1 second).
Of the 17,195 patients, 5,623 (33%) demonstrated airway hyperresponsiveness. The relationship between BMI and airway hyperresponsiveness increased in stepwise fashion, from an odds ratio (OR) of 1.15 for obesity class 1 to an OR of 1.46 for obesity class 2 and an OR of 1.50 for obesity class 3.
"We need more analysis to see if the effect of obesity on airway hyperresponsiveness is still there when we correct for lung volume [measures] like the FEV1," said Dr. Labrecque, a pulmonologist at the hospital who is also affiliated with the department of medicine at the University of Montreal. "If the relation between BMI and airway hyperresponsiveness disappears after this correction, that could mean that it is not the fat itself that is responsible for the risk of asthma, but its mechanical effect on the lung’s volume."
In their poster, the researchers stated that if asthma is added to the list of conditions related to obesity, "then reducing the prevalence of obesity could be expected to produce even greater public health benefits than are currently estimated."
Dr. Labrecque said that she had no relevant financial conflicts to disclose.