Asthma is a disease with distinct phenotypes that have implications for both prognosis and therapy. Epidemiologic studies have demonstrated an association between asthma and obesity. Further studies have shown that obese asthmatics have poor asthma control and more severe asthma. This obese-asthma group may represent a unique phenotype. The mechanisms behind poor asthma control in obese subjects remain unclear, but recent research has focused on adipokines and their effects on the airways as well as the role of oxidative stress. Both surgical and nonsurgical weight loss therapy have shown promising results with improvements in asthma control and decreased asthma severity. Comorbid conditions such as gastroesophageal reflux disease and obstructive sleep apnea may also have a role in poor asthma control in obese asthmatics. Further research is needed to define the mechanisms behind this phenotype which will guide the development of targeted therapies. 1. Introduction to the Obese-Asthma Phenotype Obesity and asthma are major public health problems affecting large numbers of individuals across the globe. Obesity is often classified using body mass index (BMI) (Table 1) . Worldwide obesity has more than doubled since 1980. In 2008, more than 1.4 billion adults, ≥20 years, were overweight. Of these, over 200 million men and nearly 300 million women were obese. It is estimated that at least 2.8 million adults die each year as a result of being overweight or obese . Table 1: WHO body mass index (BMI) Classification [ 1]. The World Health Organization estimates that 235 million people currently suffer from asthma and that asthma is under diagnosed and undertreated . Asthma prevalence (the percentage of people who have ever been diagnosed with asthma and still have asthma) increased from 7.3% in 2001 to 8.4% in 2010 in the United States . In 2010, an estimated 25.7 million people had asthma: 18.7 million adults aged 18 and over, and 7.0 million children aged 0–17 years . Both cross-sectional epidemiologic investigations and prospective studies have shown an association between asthma and obesity with a relative risk (RR) of up to 3.0 [5–8]. A meta-analysis of seven prospective studies showed an increased odds ratio (OR) for incident asthma of 1.92 (1.43–2.59) in those with obesity versus normal weight and concluded that the odds of incident asthma increased by 50% in overweight/obese individuals . There was a dose-response relationship between body weight and asthma with increasing odds of incident asthma as BMI increased ( for trend) .
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