A previous diagnosis of asthma increases the risk for subsequent type 1 diabetes (T1D) by 41%, but a previous diagnosis of type 1 diabetes decreases the risk of subsequent asthma by 18% according to a Finnish study published in the International Journal of Epidemiology.
Researchers conducted a large, nationwide, case-cohort study in Finnish children born between January 1, 1981 and December 31, 2008. Children who were diagnosed with asthma (n=81,473) or T1D (n=9541) up to aged 16 years by the end of 2009 were identified from the Central Drug Registry. A 10% random sample was selected from each birth year cohort to serve as a reference cohort (n=171,138). The investigators used a multistate modeling approach to estimate transition rates between healthy and disease states from birth.
A total of 80,871 children with only asthma, 8939 with only T1D, and 602 children with both disorders were identified. In children with both disorders, 75.7% had asthma diagnosed before T1D, 20.9% had T1D diagnosed before asthma, and 3.3% had both diseases diagnosed within the same month. Median age at diagnosis was 4.6 years for asthma and 7.5 years for T1D.
Children with asthma were more likely to develop T1D than healthy children (0.6% vs 0.4%), but asthma developed less frequently in children with T1D than in healthy children (1.7% vs 2.7%).
A number of study limitations were noted, including the inability to verify the initial starting point of the disease process and the absence of information on some important environmental factors affecting the development of both diseases, such as infections and nutritional factors, which may have contributed to residual confounding.
The investigators suggested that the inhaled corticosteroids often used in the treatment of asthma may underlie the association between asthma and T1D, although the role of corticosteroid therapy in the pathogenesis of the disorder is still debated. As a consequence, they called for more studies to extricate the relationship between the 2.
The association between the 2 autoimmune disorders is more complex than originally believed, the researchers noted, and its direction depends on the sequence in which the disease states occur.
Metsala J, Lundqvist A, Virta LJ, et al. The association between asthma and type 1 diabetes: a paediatric case-cohort study in Finland, years 1981-2009 [published online December 2, 2017]. Int J Epidemiol. doi:10.1093/ije/dyx245