Insulin resistance potentiates the association between obesity and pediatric asthma, but this relationship appears inconsistent in relatively small studies of adults. We investigated effect modification in adults using a large, nationally-representative database.
Data were obtained from the National Health and Nutrition Examination Survey 2003-2012. Insulin resistance and a history of physician-diagnosed current asthma were obtained from 12,421 adults (ages 18—85 years). Logistic regression was used to determine associations between obesity and current asthma, adjusting for age, sex, race/ethnicity, poverty index ratio, and smoking status. We evaluated effect modification by insulin resistance of the obesity-asthma association.
As expected, obesity was positively associated with current asthma, with 97% greater odds of current asthma for obese participants (95% CI 1.64—2.36). Insulin resistance modified this association, with a stronger obesity-asthma association among those with insulin resistance (P interaction=0.03). Effect modification was also significant with obesity measured as waist circumference and waist-to-height ratio. Stratifying by tertiles of insulin resistance, analyses of the relationship between obesity and current asthma showed an ordinal relationship, with OR increasing with greater insulin resistance (1.99, 2.69, 2.95, respectively). Subgroup analysis of participants not on insulin replacement therapy also showed a significant association (P interaction=0.048). Hypertension and hypertriglyceridemia (components of the metabolic syndrome, along with obesity and insulin resistance), did not modify the obesity-asthma association (P interaction=0.68 and 0.45, respectively).
In this large, nationally-representative sample, insulin resistance modified the association between obesity and current asthma in adults. Clinical and basic studies are needed to better understand this important interaction.