Obesity has emerged as a risk factor for the development of asthma and for increased asthma severity. However, the precise mechanisms by which obesity affects the development of asthma and increases its severity remain unclear. It is speculated that a wide range of obesity-related factors are involved in the mechanisms.
Recently, two phenotypes have been identified in obesity and asthma, a late-onset and non-type 2 predominant type and an early-onset and type 2 predominant type. The former is considered 'asthma consequent to obesity' and the latter is considered 'asthma complicated by obesity'. In addition, in oriental populations including the Japanese, asthma severity and control are reported to be modified by obesity-related factors even when the patient's body mass index is between 25kg/m² and 30kg/m² while in Western populations they are modified by obesity-related factors when the patient's body mass index is equal to or more than 30kg/m². This variation in pathophysiology in obesity-linked asthma needs to be considered in clinical practice and when conducting clinical investigations.