Tara Haelle

June 18, 2017

HELSINKI — A link between the development of asthma and the development of type 1 diabetes appears to exist, but the direction of the association depends on which condition exists first, a new study suggests.

"The association between asthma and type 1 diabetes is more complex than we previously thought," explained lead author Johanna Metsälä, PhD, an epidemiologist at the National Institute for Health and Welfare, Helsinki, Finland.

"Prior asthma increased the risk of type 1 diabetes, but prior type 1 diabetes decreased the risk of subsequent asthma," Dr Metsälä told attendees here at the European Academy of Allergy and Clinical Immunology (EAACI) Congress 2017.

"This association was seen at all ages. This was a fairly novel observation," she added.

The association between asthma and type 1 diabetes is more complex than we previously thought. Dr Johanna Metsälä

Past research looking at the two diseases has had inconsistent results, with inverse, direct, and no associations all reported in the evidence. Dr Metsälä and colleagues therefore conducted a large case-cohort study that took into account timing, patient risk, possible modifying factors, sequential order of the conditions, and disease process progression.

Using data from several national Finnish health and population registries, the study included all children born from 1981 to 2008 who had been diagnosed with asthma or type 1 diabetes either by age 16 years or by 2010. Children with these conditions were identified on the basis of insulin and antiasthmatic drug purchases from Finland's drug prescription register. A total of 80,871 children had been diagnosed with asthma, 8939 had type 1 diabetes, and 602 had both.

The reference cohort of 171,138 children came from a 10% random sample of each birth cohort from those years. Data on maternal background and perinatal factors came from the medical birth register.

The researchers divided the children into groups by birth year (ages 0 - 3, 4 - 7, 8 - 11, and 12 - 16 years) to analyze their transition rates between four states: no asthma and development of type 1 diabetes, having only asthma, having only type 1 diabetes, and having asthma and type 1 diabetes.

After adjustment for sex and birth decade, the analysis revealed that having a prior diagnosis of asthma increased the risk for type 1 diabetes by an average of 41% (95% confidence interval, 1.28 - 1.54). Having a prior diagnosis of type 1 diabetes, however, decreased the risk for later asthma by 18% (95% confidence interval, 0.69 - 0.98).

Study Limitations

Although the study included a large, population-based cohort with minimal opportunity for recall bias, it was unable to account for the initial starting point of each disease process. The researchers were also unable to individually confirm all the diagnoses and lacked data on some potential confounders, such as dietary factors or infections relevant to both diseases.

"This may not be a problem with type 1 diabetes, where the diagnosis is relatively straightforward, but in asthma, particularly in young children, the diagnosis is difficult," said Dr Metsälä, adding that information on different phenotypes or atopic background was also not included.

She also noted that bias or unaccounted-for confounders may explain part, or all, of the association seen in the study. Another possibility is that medication for either disease could be playing a role, she added.

Dr Metsälä did not have any explanations for the findings, but said that learning more about the biological mechanisms underpinning the relationship between asthma and type 1 diabetes might help explain the etiology of both diseases.

You would think there is likely to be a link between the two diseases because they share so many environmental and temporal risk factors. Dr Peter Vuillermin

One of the meeting attendees, Peter Vuillermin, PhD, a professor of pediatrics at Deakin University in Geelong, Victoria, Australia, raised the possible involvement of other autoimmune conditions as a connecting factor.

"You would think there is likely to be a link between the two diseases because they share so many environmental and temporal risk factors," Dr Vuillermin told Medscape Medical News.

"I think comparing them and trying to understand what the similarities and differences are is likely to be really informative," he added. "It would be also nice to know if there's a link across other allergic conditions that use different medications, such as food allergy."

Dr Metsälä said they did not have any information on medications, such as epinephrine prescriptions, beyond the data on insulin and bronchodilator prescriptions. She also emphasized how interesting it was that the association occurred at all age levels.

"We really don't have a good explanation," she said. Immunological explanations are possible, she added, but not yet hypothesized.

No external funding was reported. Dr Metsälä and Dr Vuillermin have disclosed no relevant financial relationships.

European Academy of Allergy and Clinical Immunology (EAACI) Congress 2017: Abstract 0204. Presented June 18, 2017.

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