​Risk of type 1 diabetes may depend on where childhood is spent

Did you grow up in the serene countryside or a city full of skyscrapers? Wondering why? Well, it has a lot to do with your risk of developing type 1 diabetes. Yes, that’s right. A new study found that where you spent your first five years of life is a defining factor in developing type 1 diabetes in the future.
A new research, which is set to be presented at this year’s Annual Meeting of the European Association for the Study of Diabetes (EASD) to be held in Vienna, Austria from September 15-19, found that the location where you spent your childhood could determine the risk of developing type 1 diabetes. And it's not what you think!

​Type 1 diabetes (T1D) is a chronic autoimmune disease where the pancreas makes little or no insulin. This happens because the immune system in the body attacks and destroys insulin-producing cells in the pancreas, called beta cells, by mistake.
Insulin is a hormone crucial for regulating blood sugar levels. Without sufficient insulin, glucose (sugar) builds up in the bloodstream, causing hyperglycaemia (high blood sugar). Though this type of diabetes is typically diagnosed in childhood, adolescence, or young adulthood, it can occur at any age. Most people with this condition may require insulin replacement therapy for the rest of their lives.

While living in the city as compared to the countryside is often assumed to be unhealthy, the same cannot be said for the risk of developing type 1 diabetes. Yes, that’s right. This study, led by Samy Sebraoui and Professor Soffia Gudbjornsdottir, University of Gothenburg, Sweden, and colleagues, found that living in living in a rural environment in the first five years of life could increase the risk of developing type 1 diabetes compared with living in urban environments.

Sweden has the second-highest global incidence of T1D, with geographical variation suggesting environmental risk factors. Previous studies have mostly looked at where patients lived when they were diagnosed with T1D, and only a few have examined their location at birth or before symptoms appeared. This new study, however, tracked people in Sweden from birth to the time of diagnosis, to identify high and low-risk clusters over different life periods.
They found that all the people diagnosed with T1D during 2005-2022 (ages 0-30 years) were identified in the Swedish National Diabetes Register. Their residential address from birth to diagnosis were collected, and also used zonal statistics to identify where they lived for the first five years of life.

The researchers found that 21,774 patients aged 0 to 30 years were diagnosed with T1D between 2005 and 2022. Among these 58 % were male. 15,426 (around three quarters) were under 18 years old during the time of diagnosis. The mean age at diagnosis was 13.6 yrs (males 14.1, females 12.9). 24 % of patients had relocated to a different municipality from birth to diagnosis.
They found four high-risk clusters for type 1 diabetes in central rural areas (all in the countryside, away from urban centres). These individuals relative risk of developing T1D was between 30% and 80% higher.. No high-risk clusters were observed in people in major cities. In larger cities, low-risk clusters were seen, with 20% to 50% lower (within the largest cities such as Stockholm, Gothenburg and Malmö) risk of developing T1D.

“This finding was unexpected and highlights the need for environmental studies to investigate potential risk factors in rural areas, as well as possible protective factors in urban settings. In Sweden, we have access to highly detailed environmental data covering the entire country, providing a unique opportunity to better understand the development of type 1 diabetes,” the researchers said.
“There is a clear geographical variation in the incidence of type 1 diabetes in Sweden. The first 5 years of life exhibited the strongest association with high- and low-risk clustering. Our findings facilitate further research into environmental factors potentially influencing development of type 1 diabetes. We hypothesise that the exposure of environmental factors, predominantly in rural areas and primarily during the first five years of life, elevates the risk for developing type 1 diabetes,” they added.

The researchers also discussed some possible theories behind this unusual finding, and said it could be studied further. “Viral infections are more common in early life in urban areas and that could protect a person from future autoimmune diseases including type 1 diabetes. Living in rural areas could be associated with more exposure, for example, to pesticides and allergens. This is only speculation, but we have very good data to be able to investigate this in detail in future studies,” they said.
“These findings were previously unknown and unexpected - it was a surprise that that living in larger cities came with a lower future risk of type 1 diabetes. We will study in detail different environmental factors that might be protective or increase risk. We will also look into different lifestyles in urban versus rural areas,” the authors added.