Obesity is a risk for asthma and wheeze but not airway hyperresponsiveness

A study was undertaken to assess whether the recent increases in prevalence of both asthma and obesity are linked and to determine if obesity is a risk factor for diagnosed asthma, symptoms, use of asthma medication, or airway hyperresponsiveness.

Data from 1971 white adults aged 17-73 years from three large epidemiological studies performed in NSW were pooled. Doctor diagnosis of asthma ever, history of wheeze, and medication use in the previous 12 months were obtained by questionnaire. Body mass index (BMI) in kg/m(2) was used as a measure of obesity. Airway hyperresponsiveness (AHR) was defined as dose of <3.9 micromol histamine required to provoke a fall in forced expiratory volume in one second (FEV(1)) of 20% or more (PD(20)FEV(1)). Adjusted odds ratios (OR) were obtained by logistic regression.

After adjusting for atopy, age, sex, smoking history, and family history, severe obesity was a significant risk factor for recent asthma (OR 2. 04, p=0.048), wheeze in the previous 12 months (OR 2.6, p=0.001), and medication use in the previous 12 months (OR 2.83, p=0.005), but not for AHR (OR 0.87, p=0.78). FEV(1) and forced vital capacity (FVC) were significantly reduced in the group with severe obesity, but FEV(1)/FVC ratio, peak expiratory flow (PEF), and mid forced expiratory flow (FEF(25-75)) were not different from the group with normal BMI. The underweight group (BMI <18.5 kg/m(2)) had increased symptoms of shortness of breath, increased airway responsiveness, and reduced FEV(1), FVC, PEF, and FEF(25-75) with similar use of asthma medication as subjects in the normal weight range.

Although subjects with severe obesity reported more wheeze and shortness of breath which may suggest a diagnosis of asthma, their levels of atopy, airway hyperresponsiveness, and airway obstruction did not support the suggestion of a higher prevalence of asthma in this group. The underweight group appears to have more significant respiratory problems with a higher prevalence of symptoms, reduced lung function, and increased airway responsiveness without an increase in medication usage. This group needs further investigation.