Risk of asthma in adult twins with type 2 diabetes and increased body mass index

P>Aim: To examine the relationship between asthma, type 2 diabetes and increased body mass index (BMI) in adult twins. Methods: We performed record linkage between questionnaire-defined asthma and BMI, and hospital discharge diagnoses of type 2 diabetes in 34 782 Danish twins, 20-71 years of age. Results: The risk of asthma was increased in subjects with type 2 diabetes relative to nondiabetic subjects both in men (13.5%vs 7.5%), P = 0.001 and in women (16.6%vs 9.6%), P = 0.001. The result remained significant after adjustment for age, BMI, smoking, symptoms of chronic bronchitis, marital status and zygosity, men: OR = 1.70 (1.07-2.70), P = 0.026; women: OR = 1.88 (1.24-2.85), P = 0.003. In this analysis, BMI remained a highly significant predictor for asthma independently of diabetes status in women, P < 0.000 but not in men, P = 0.336. Significant positive genetic correlations were found between asthma and type 2 diabetes, 0.20 (0.01-0.40), P = 0.047; between asthma and BMI in women, 0.15 (0.07-0.22), P < 0.000; and between BMI and type 2 diabetes, 0.40 (0.29-0.43), P < 0.000. Conclusions: Asthma, type 2 diabetes and increased BMI are strongly associated in adults, particularly in women. These results suggest a common aetiology for asthma and metabolic syndrome.