Metabolic syndrome and insulin resistance appear to contribute to the pathogenesis of asthma in obese children and adolescents.

Erick Forno, MD, MPH, from the Children’s Hospital of Pittsburgh in Pennsylvania, and colleagues published the results of their cross-sectional study online March 4 in the Journal of Allergy and Clinical Immunology.
“To the best of our knowledge, this is the first study of insulin resistance or [metabolic syndrome] and lung function in a representative sample of US adolescents with and without asthma,” the authors write. “Among adolescents with and without asthma, we found that insulin resistance is associated with decreased FEV1 and FVC values and that [metabolic syndrome] is associated with lower FEV1/FVC ratios.”

The study used a representative sample of US adolescents and was performed by uniformly trained personnel using standardized procedures. The investigators reviewed data from 1429 adolescents aged 12 to 17 years enrolled in the 2007 to 2010 National Health and Nutrition Examination Survey, only 95 of whom had current asthma. The study did not control for diet or family history of diabetes.

The investigators found that both insulin resistance and metabolic syndrome are associated with significantly worsened lung function (2% – 10% decrease in FEV1/FVC) in adolescents who are overweight or obese. Specifically, metabolic syndrome was associated with a 2% decrease in lung function compared with healthy teenagers. Asthma alone was linked to a 6% reduction in lung function, and the combination of metabolic syndrome and asthma was associated with a 10% decrease. The results remained significant after controlling for other factors, including body mass index and waist circumference.

The study design precluded, however, the establishment of a temporal relationship among insulin resistance, metabolic syndrome, and lung function. The researchers analyzed only current asthma and did not identify adolescents who had low exacerbation risk but higher impairment before the study began.

Adolescents were classified as having metabolic syndrome if they met three of five criteria: fasting glucose levels of 110 mg/dL or higher, waist circumference in the 75th percentile or higher, fasting triglyceride levels of 100 mg/dL or higher, high-density lipoprotein levels of 50 mg/dL or lower, and systolic blood pressure in the 90th percentile or higher.

Although previous studies have been published on asthma and insulin resistance, the current study adds to the discussion by quantifying lung function.

“I think it really reinforces the need to screen for metabolic syndrome and insulin resistance,” emphasized Grace Kim, MD, from Seattle Children’s Hospital in Washington, to Medscape Medical News.
Dr Kim points out, however, that “they don’t really comment about people’s puberty status,” adding that “with puberty, kids are in a more insulin-resistant state.” Nor does the study examine visceral obesity.

Dr Kim explained that endocrinologists already know that children and adolescents who are overweight tend to have asthma. “They are finding what we know anecdotally,” she explained.

Insulin resistance may affect lung function via insulin growth factor 1, adiponectin, or leptin. Metabolic syndrome may affect lung function via increased protein turnover and consequent altered arginine metabolism.

Insulin resistance has been associated with hepatic steatosis and cardiovascular disease. Metabolic syndrome has been associated with asthma in adults, and one study linked it to reduced lung function.