Insulin resistance as a predictor of incident asthma-like symptoms in adults

There is accumulating evidence that obesity is associated with an increased risk of asthma. It has been hypothesized that insulin resistance may be involved in obesity-induced asthma, but till date there is no prospective data on this issue. To investigate the association of obesity and insulin resistance with the incidence of asthma-like symptoms in adults. Out of a random sample of 12 934 persons from a general population, 6784 (52.5%) were included and participated in a health examination in 1999-2001. After 5 years they were re-invited and 4516 (66.6%) participated at follow-up. At baseline three obesity measures were considered: body mass index, waist circumference, and waist-to-hip ratio. In addition, fasting glucose and insulin were measured for determination of insulin resistance. Information on asthma-like symptoms at baseline and follow-up were obtained by questionnaires. A total of 3441 participants defined as non-asthmatic at baseline and with complete information on all the considered variables were included in the analyses. Data were controlled for confounding by sex, age, social status, and smoking. All obesity measures were associated with incident wheezing and asthma-like symptoms. In addition, insulin resistance was associated with incident wheezing [odds ratio (OR) 1.87, 95% confidence interval (CI) 1.38-2.54] and asthma-like symptoms (OR 1.61, 95% CI 1.23-2.10). The effect of insulin resistance was stronger than that of obesity and was independent of sex. We found that insulin resistance was associated with an increased risk of developing asthma-like symptoms. This finding supports the hypothesis that obesity and asthma may be linked through inflammatory pathways also involved in insulin resistance.