Introduction
There is increasing evidence to suggest an association between asthma and obesity, shown by both cross-sectional and prospective studies in adults 1,2. Mechanisms explaining this link include compromised lung mechanics as a consequence of obesity, decreased physical activity due to asthma leading to obesity, genetic factors shared by both pathologies, asthma associated co-morbidities (gastroesophageal reflux disease and sleep disordered breathing), which are also common in obese subjects and last but not the least, the inflammatory effects of the metabolic changes associated with weight gain 3. Studies have identified certain metabolic derangements as potential risk factors, important among them being derangement of lipid profile as well as a state of insulin resistance (IR) 4-6.
The current view is that these metabolic derangements could form the link between obesity and asthma, by resulting in a state of chronic inflammation, also affecting the airway. Logically, the prevalence of these metabolic abnormalities would then be higher in patients with asthma. Not only there is evidence to support this hypothesis, but it can also be demonstrated that there is some influence on the severity of asthma symptoms 7.
An adult population-based study in Denmark found that IR was associated with increased risk of aeroallergen sensitization and allergic asthma but not non-allergic asthma 8. A small cross-sectional pediatric study conducted in Australia showed the prevalence of IR, defined by a HOMA-IR (Homeostasis Model Assessment Insulin Resistance) value of > 1.77 to be much higher among allergic asthmatics (42%) as compared to healthy controls, of whom none had IR9. A study conducted in Taiwan in children showed the levels of total cholesterol (TC) and low-density lipoprotein (LDL) to follow the order, obese asthmatics > non-obese asthmatics > obese controls > non-obese controls, thus suggesting a relationship between asthma and dyslipidemia, which was amplified by obesity 10.
However, there are studies that fail to confirm these proposed associations and some that even provide evidence to the contrary6,11. For example, spirometry parameters, asthma severity and Asthma Control Test (ACT) scores did not differ between obese and non-obese children with asthma, in Cleveland, Ohio12. Consequently, the data regarding the prevalence of metabolic abnormalities in children with asthma are not consistent and the mechanisms relating obesity and asthma have not been clearly elucidated. If adequately proven, this has therapeutic implications, helping in better management and even prevention of development of asthma like symptoms. Therefore, we conducted this study to determine the prevalence of metabolic abnormalities including IR, metabolic syndrome (MS) and dyslipidemia in children with asthma, and to find out if these metabolic abnormalities showed an association with asthma symptom control and lung function.