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.