Type 1 diabetes geographic variability implicates environmental triggers
medwireNews: Researchers uncover geographic heterogeneity in type 1 diabetes incidence across England, and identify demographic and environmental factors significantly associated with this variability.
Susan Hodgson (Imperial College London, UK) and colleagues conducted “an agnostic, ecological environment-wide association study” in which they matched 53 variables to 13,948 incident type 1 diabetes cases in children aged 0–9 years between April 2000 and March 2011.
They did the analysis at the level of the local authority district, of which they say there are 354 in England, each with an average population of about 140,000.
The researchers found that 30 demographic and environmental factors were significantly associated with type 1 diabetes incidence, with the associations being inverse (ie, protective) in all but four cases.
After further accounting for spatial dependency (ie, the likelihood of neighboring districts sharing risk factors), the team narrowed the significant risk factors down to 15. In this spatial mapping analysis, the risk for type 1 diabetes per local authority district ranged from 32% reduced to 39% increased relative to England as a whole, with the highest risks appearing to be in rural and coastal areas.
In support of this, the factors significantly associated with geographic variability in risk included those associated with urban lifestyles, such as air pollution and population density.
This pattern of risk could support the hygiene hypothesis, indicate a protective effect of some features associated with urban lifestyles, or reflect geographic variability in genetic susceptibility, Hodgson and team suggest in Diabetologia.
Because many of the variables were highly correlated with each other (eg, air pollution variables), the researchers selected representative non- or weakly correlated factors to include in a final ecologic regression analysis. These were nitrogen dioxide (representing air pollution), lead in soil, radon potential class, ethnicity, overcrowding, and Index of Multiple Deprivation (IMD) living environment domain.
In this model, IMD living environment domain (encompassing both poor home and outdoors environments) remained significantly protective against diabetes risk, in line with the protective effect of an urban environment in the other models.
By contrast, radon potential (the likelihood for an area having high radiation) was associated with a significantly increased risk. The researchers note that high radon potential in England is more likely in rural areas, and they add: “We could find no other studies specifically linking radon exposure to type 1 diabetes to support our finding.”
Hodgson and colleagues stress that “there remains a risk of false-positive results and potentially important confounders which we could not assess” and call for further studies at an individual level.
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