Researchers from the Colorado School of Public Health at the Anschutz Medical Campus have examined whether any environmental exposures can explain why type 1 diabetes is on the rise. They published their study (“Type 1 diabetes—early life origins and changing epidemiology”) in Lancet Diabetes & Endocrinology.

“Type 1 diabetes is a chronic, immune-mediated disease characterized by the destruction of insulin-producing cells. Standardized registry data show that type 1 diabetes incidence has increased 3–4% over the past three decades, supporting the role of environmental factors. Although several factors have been associated with type 1 diabetes, none of the associations are of a magnitude that could explain the rapid increase in incidence alone. Moreover, evidence of changing prevalence of these exposures over time is insufficient,” the investigators wrote.

“Multiple factors could simultaneously explain the changing type 1 diabetes incidence, or the magnitude of observed associations could have been underestimated because of exposure measurement error, or the mismodeling of complex exposure-time-response relationships. The identification of environmental factors influencing the risk of type 1 diabetes and increased understanding of the cause at the individual level, regardless of the ability to explain the changing incidence at the population level, is important because of the implications for prevention.”

Identifying environmental factors associated with type 1 diabetes that influence its incidence can inform future preventive trials and searches for other environmental risk factors. In this paper, the team reviewed the literature on environmental factors like air pollution, diet, childhood obesity, the duration of breastfeeding, the introduction of cow’s milk, infections, and many others that showcase an impact on type 1 diabetes. The researchers then looked at the prevalence of exposure over time while varying its annual increase under simulated scenarios. Using the simulated data, the research showed that if a single factor were to explain the changes in the incidence of type 1 diabetes over the past few decades, it would have to be very strongly associated with the risk of type 1 diabetes.

The simulated scenarios showed that an environmental factor that increased at a constant rate from nearly absent in the population to nearly ubiquitous would have to confer a relative risk of 5 to explain an approximately 3% annual increase in the incidence of type 1 diabetes. However, most of the environmental factors reviewed had a relative risk of less than 2.

“While several factors have been associated with type 1 diabetes, none of the associations are of a magnitude that can explain the rapid increase in incidence alone,” said Jill Norris, PhD, professor and chair of epidemiology at the Colorado School of Public Health and lead author of the paper. “Moreover, evidence of the changing prevalence of these same exposures over time is not convincing nor consistent.”

The paper explained that more research is required, and it is possible that multiple factors simultaneously may account for the increase in type 1 diabetes cases. Other factors are that the magnitude of observed associations may have been underestimated due to exposure measurement error or mismodeling of complex exposure-time-response relationships.

The study concluded that the identification of environmental factors influencing type 1 diabetes risk and increased understanding of the etiology at the individual level, regardless of the ability to explain the changing incidence at the population level, is important because of the implications for prevention.

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