The association between asthma and type 1 diabetes, two chronic, immune-mediated diseases, has been of longstanding interest, but the evidence is still conflicting. We examined this association in a large, nationwide case-cohort study among Finnish children, using a novel statistical approach.
Among the initial cohort of all children born between 1 January 1981 and 31 December 2008, those who were diagnosed with asthma (n?=?81 473) or type 1 diabetes (n?=?9541) up to age 16 years by the end of 2009 were identified from the Central Drug Register maintained by the Social Insurance Institution of Finland. A 10% random sample from each initial birth year cohort was selected as a reference cohort (n?=?171 138). The association between asthma and type 1 diabetes was studied using a multistate modelling approach to estimate transition rates between healthy and disease states since birth. Hazard ratios (HRs) with 95% confidence intervals (CIs) were calculated to represent the change in the transition rate between the disease states.
After adjusting for sex and birth decade, previous diagnosis of asthma increased the risk of subsequent type 1 diabetes by 41% (95% CI: 1.28, 1.54), whereas previous diagnosis of type 1 diabetes decreased the risk of subsequent asthma by 18% (95% CI: 0.69, 0.98).
The findings of the present study imply that the association between the diseases is more complex than previously thought, and its direction depends on the sequential appearance of the diseases.