Smoking and obesity are modifiable risk factors that have been associated with a higher prevalence of asthma, more severe asthma, and worse asthma control. These two risk factors have also been found to be associated with a reduction in the effectiveness of inhaled corticosteroids (ICS), potentially leading higher prescribed doses. To our knowledge, no study has assessed the joint impact of smoking and obesity on ICS dose The present study assessed the interaction of smoking and obesity on prescribed ICS dose in adult asthmatics.
500 patients (60% women, mean age±SD = 49±14 years, ICS dose = 654±512 fluticasone equiv., BMI = 27±5 kg/m2) with physician-confirmed asthma were recruited from an outpatient asthma clinic. Detailed information about smoking habits (used to calculate total pack-years), height, and weight (used to calculate body mass index (BMI)) was collected. Patients also provided information on their asthma medications (dosage and frequency of administration), which was verified by chart review.
Analysis using pack-years, BMI, and daily prescribed ICS dose as continouous varibles (controlling for age, sex, education level, and duration of asthma) found a significant main effect of smoking on ICS dose (F=6.40, p=.012). There was also a significant smoking X BMI interaction on ICS dose (F=4.89, p=.027). There was no main effect of BMI on ICS dose (F=3.01, p=.083).
Results indicated that patients who had the highest levels of lifetime smoking were prescribed the highest doses of ICS. The results also suggest that smoking has a stronger influence on prescribed ICS dose in those with lower versus higher BMI's. However, those patients who smoked the most, and had the highest BMI's, were generally prescribed the highest doses of ICS's.
These findings suggest that assessment of lifetime smoking and current obesity should be part of the standard evaluation of patients with asthma. Also, smoking cessation and weight reduction interventions may significantly impact the daily dose of ICS needed to control asthma, though further research is needed to confirm this.
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